On 12th February 2025, were joined by butterfly expert, Mike Slater, for a talk on the small blue butterfly, the second talk in our Winter Talk Series. We learnt more about the small blue, its egg-laying habits and preferences, and about the action we can take to support this rare butterfly, using conservation action in Warwickshire as a case study.
Watch the full talk on YouTube below. If you are interested in getting involved in helping the small blue and are based on either the north or east coast of Scotland, get in touch with your local officer to find out how you can help:
North Coast: Sarah Bird – sarah.bird@plantlife.org.uk
East Coast: Tracy Munro tmunro@butterfly-conservatio.org
Transcript
Eilidh Ross, Species on the Edge [00:03 – 02:16]
Welcome, everyone. Welcome to the second of our winter talks here with Species on the Edge. Lovely to have you all. I’m Eilidh, I’m the Communications Manager for Species on the Edge and I will be co-hosting the talk tonight alongside Liz, my colleague. She’s going to take over for the Q&A session later on.
So I’ll just give a wee introduction to Species on the Edge and then we can get going. A lot of you might know what Species on the Edge is but for those who don’t, Species on the Edge is a programme, so we’re working to support 37 of Scotland’s rarest and most vulnerable coastal and island species, one of which is the small blue butterfly, which we’ll hear more about tonight.
We’ve got teams in seven project areas around Scotland and there our area teams are working with communities in those areas to help them support their local vulnerable species, their local target species for the programme, with the hope of securing a sustainable future for these species on our shores.
I should say, why are we focused on coasts and islands? So, Scotland’s coast and islands provide a last refuge for some of the UK’s most vulnerable species. And also sort of the last refuge on a UK scale, but also on a global scale so they really do provide an important place for a lot of these species and so it’s important that communities in these areas can be supported in taking action for their local populations and ensure the continued survival of our target species.
So, like I said, so we’re a partnership programme; we’ve got eight partner conservation organisations that take part in the programme. We’re sharing staff, money and expertise to offer the most effective, informed and impactful action and support as possible. And I should also say we’re funded by The National Lottery Heritage Fund, so shout out always goes to them and all lottery players.
You can go look up our website if you want to find out more. Lots of opportunities to get involved and learn more about the programme.
But that’ll probably do us for now on that. And now I’d love to introduce Mike Slater. Mike, you can properly introduce yourself, but I’ll hand over to you now. And yes, very excited for this talk.
Mike Slater [02:16 – 32:42]
Well, first thing is, welcome to everybody. Just a bit of background about myself: I’ve been involved in doing practical conservation for over 35 years. But today’s talk is about really giving you some of the background about the small blue. Then I’m going to talk a little bit about the history of the small blue in the West Midlands area. Then, we’ve done a lot of research in the West Midlands, so I’m going to tell you what that research entailed. Finally, I’m going to say what you can do to conserve the small blue and, particularly, does it work?
So, without further ado, this is a small blue. It’s our smallest UK butterfly. It measures 18 to 27 millimeters from wing to wing. And I love this photograph because it actually shows you how small the butterfly is. It fits into the top of a buttercup – that just shows you how diminutive it is. Round the Warwickshire way, it actually flies from the end of May to the first two weeks of June. And looking around the country when I did some research for this talk, that seems to be fairly general. Unfortunately, I don’t quite know how much it will differ in Scotland.
Again, most parts, certainly in England, has a second brood of small blues and this comes out in late July and early August. So again, that’s probably similar in Scotland. It might not occur as second brood every year.
Now, this is the first interesting fact. They’ve done mark and recapture experiments with a small blue, like many other butterflies. And this is where they put a unique mark on the butterfly’s wing, keep catching it from day to day and they find out how long the butterfly lives but also how much it flies from where he was born. And the average, they found out, was just 40 meters, a very small distance. But that doesn’t really tie in with actually its ability to colonise new sites. Now, certainly in the Midlands, we know it’s colonised new sites three to five kilometres away from where we know a colony exists and we pretty much know where all the colonies exist. And what we think happens is this butterfly has the ability to smell out kidney vetch, and then it flies upwind to find the new areas where kidney vetch is and colonises them.
Like most butterflies, it nectars and it seems to have a particular penchant for yellow flowers. In particularly common birds foot trefoil and kidney vetch. But it also will go down and nectar on horrible things like dog poo and fox scat. It also takes minerals from the soils. especially for the males, we think they do this to get certain minerals to make the males fertile. But there’s more research needed in that area.
Around the UK, it’s got three main habitats: that’s chalk limestone grasslands; dunes; and brownfield post-industrial habitats. But like most things, it’s all got common features. So all these types of habitats, first of all, they’re sheltered and warm. That’s important for a small butterfly like this. The soils the kidney vetch grows in are nutrient poor; there’s always a high percentage of bare ground and that’s important and I’ll come back later to that in the talk.
Surprisingly, it seems to be able to survive on just 50 kidney vetch plants to form a colony, and we’ve looked at this in detail, and we think 200 square meters of good habitat can support a colony of small blues.
Again, similar to nutrient poor, that soils are always free draining, skeletal in nature. The sites generally lack scrub or there’s a small amount of scrub and I’ll come back to that bit later as well.
Because it’s a small butterfly it has to nectar a lot; there’s always a high abundance of nectar sources. Another key aspect is they need overnight roosting sites and, when we look at the sites, heavy grazing is bad and certainly we don’t want to see grazing in the spring and summer.
Now, the first problem that the small blue’s got is that the kidney vetch is classified as a short-lived perennial; that means it only survives for about three or four years before the whole plant dies. And in general, the kidney vetch isn’t a plant that’s well adapted to our modern environment.
Now I’m going to come on to the history of the species in the West Midlands. There’s a picture of the map of the West Midlands and it used to occur in all six counties of the West Midlands.
But by 2009, it was extinct in Shropshire, Staffordshire, Hereford, Worcestershire, the metropolitan County of Birmingham, and it only survived in Warwickshire, and only three colonies survived. And in Warwickshire, it had suffered an 84% decline. So really, it was heading for a regional extinction. And so, we set up, eventually, a small blue project to try and conserve it and turn around its fortunes.
This is a map of the area where the small blue existed and really what I want you to look at is where the last three colonies were. If you look at the cursor, there was a colony here at Bishop’s Hill, another one here at Bishop’s Bowl and finally, the last colony there, was at Southam Quarry but you can see that’s five kilometres apart, but again, I’ll come back to this, but look at that line there. That’s what we call the Southam Bypass and I’ll talk about that in more detail later.
So when we set up the project, we know that butterflies survive better in what’s called a metapopulation, that means a load of connected sites where the butterfly can go extinct or colonise naturally, and normally they’re very close together. So if you look at this map, you’ll see that all the green dots, they’re what we call potential sites. Now, in our terminology, that’s a site where the butterflies never existed and we have to create habitat. You might be in the right location. They’re important in conservation terms. The red dots, as you probably guessed, are where the butterfly used to be, but it’s gone extinct. And the other thing is the blue dots are where it currently is. And those who have been paying attention will suddenly say, well, hang on, there’s four dots on that map. But unfortunately, that Bishop’s Bowl fishing site went extinct just before the project started.
Now, what caused all these extinctions? Habitat destruction is always one we go to. But in Warwickshire, actually, it wasn’t really habitat destruction. Our main problem was scrub invasion. Now this shows one of the sites where the butterflies still exist. This is Bishop’s Hill. And if you look at that photograph you’ll see all the dots of yellow, that’s kidney vetch flowers. And if you look really closely, you’ll see lots of wispy hawthorn here.
Now this is a perfect habitat. The wispy hawthorn creates shelter for the butterfly and there’s lots and lots of nectar and caterpillar foodplant. But if you don’t manage sites like that, and this is another area of Bishop’s Hill where the butterfly used to occur, the scrub in just four or five years can look like this, and so that swamps out the kidney vetch and of course the butterfly goes extinct.
This is another site. This is Nelson’s Wharf and you can see here the masses of kidney vetch just in front of you. But one of the other things small blue suffer from is poor management that, of course, is related to grazing. So, those are no sheep grazing. When sheep graze they nibble very closely to the ground and cause the sward to close. That means that the plants in the grassland are very close together and there’s very little few gaps where the seed of the particular wildflower can drop down and re-germinate. And unfortunately, we had one site, it was a SSSI and actually a wildlife site as well, nature reserve, and what they did, they kept for some reason the sheep on well into the spring, and because the sheep graze as they normally do, kidney vetch is very palatable, they grazed off all the heads of the kidney vetch and so the butterfly went extinct in one year of poor grazing.
And because they’d use sheep grazing over a number of years, the sward was closed so there was no kidney vetch seed in the seed bank and so the kidney vetch also went extinct in one year.
The other thing the kidney vetch suffers from is drought. And I’ve surveyed all the sites in Warwickshire annually and I’ve noticed that when we have a drought in spring, 80% of the plants at virtually all sites die and that can cause a problem. But if there’s a lot of bare ground around, what we also find is that by the next year, because there’s seed in the seed bank, and the seed was dropped by the few flowers in flower, the kidney vetch comes back very strongly. But certainly drought is a problem. And in Warwickshire we’ve got what we call Blue Lias Jurassic clay that is like mud in the winter but in the summer it dries like concrete, so that’s again often a problem we have in Warwickshire.
The other problem with small blue: it doesn’t like wet springs. There’s another site in Warwickshire I visited called Stockton Cutting, and I went there one morning and what I found is that slugs actually crawled up the kidney vetch plants and 90% of the flower heads had been eaten off. And of course, 90% of the flower heads, that’s where the small blue lays its eggs. If they’re gone, it vastly reduces the amount of habitat there for them to egg lay on.
Now we’re coming on to the research. I had a great PhD student working with me, she was fabulous at finding eggs, and between us we found 179 eggs during our survey one year. And we measured these factors to see what’s important to the small blue.
First of all, we measured the vegetation turf height. And those who haven’t done this in the past, we use what we call a drop disk. So that’s a 15 centimeter diameter, five ply circle of wood and it drops down a doweling pole and where it stops, that’s the turf height. Now, underneath that turf height, we look for certain factors which I’ll come back to later. Also, we measured how high the flower head of the kidney vetch was where an egg was laid from the ground; just used a normal tape measure for that. We also looked at what type of flower head the small blue was using to lay its eggs. Was it fully opened? Was it half opened about to flower or was it still in bud? We also counted the number of eggs on individual flower heads. And then we noted, was the flower head isolated? Was it away from a group or clump of kidney vetch? Was it in the middle of that group or clump of kidney vetch?
And underneath the disk we basically estimated how much bare ground there was available for the kidney vetch after it finished flowering for the seed to drop and fall into.
And the next thing we managed, also under the same disk, was what percentage of green vegetation was there? Normally that’s grass, because that’s another factor. There’s a lot of grass in habitats, it cools the environment.
And finally, we looked at what the aspect was of where we found the kidney vetch flower and the egg. So was it flat? Was it sloping? And also noted the orientation to the sun.
When we did this search, we did it in really the beginning of June. We found the peak time for finding eggs was the second week of June.
When you get your eye in, I always say this and people say, no, it’s not, but it is relatively easy to find the small blue eggs. In fact, on a lot of sites, it’s easier to find the eggs of the small blue than the butterfly itself because sometimes the populations are very, very small. And the egg is blue white so it does stand out well against the general yellow flower area of the kidney vetch.
And we also look to see where it laid the egg. You can see a small blue laying an egg there. But it actually lays on this area here which is the downy calyces, as I pronounce it, and for those who don’t know it, the calyces is the bit that protects the flower as it’s bursting into flower. And so if anyone’s looking for small blue eggs, that’s the area you should concentrate on.
Though we found eggs as low as three centimetres from the ground and as high as 40 centimetres, the vast majority were found between 17 and 27 centimetres from the ground. So they generally like tall, vigorous plants.
Now bare ground is really, really important. Now, if you look at this picture, it’s another area of Nelson’s Warf you can see kidney vetch growing on a slope there. But what you want to look at is these areas here, there and there. And again, if you’re going to look for small blue eggs, these are the areas there just along the edge, those are the plants that’s more likely to have a small blue egg. Don’t bother with these. You’ll rarely find them there.
Again, if you know the kidney vetch plant well, you’ll know it’s got two colours, or two colour forms. Most of them, of course, are yellow. If you look carefully in this photograph, you’ll see the other colour, which is yellow with flecks of orange in. And when we did our research, we found that there was no difference to the egg laying. They used both colourations to the same extent.
Now, this we found really interesting: 18% – that’s a really high percentage – where we found an egg we found more than one. Some cases, I think the maximum you found was five on one flower head.
And the small blue doesn’t seem well adapted. It’s not like the orange tip females. Those who know the orange tip females, they put a chemical marker onto the plants because their caterpillars are cannibalistic like the small blue is. So, by putting the chemical marker in, what you find is as long as it’s within 24 hours, that chemical marker stops other orange-tipped females laying an egg on the same caterpillar food plant. Whereas we find so many like this with a small blue and such a high percentage they don’t seem to have this capacity for putting a chemical marker onto the food plant.
Another good way of finding small blue colonies is actually to look for their caterpillars. And we always recommend you look for the fourth instar. That’s the fourth skin change and certainly down our way that occurs in late July. When the capital first emerges from the egg, it drills a hole into the seed pods and disappears in there. And you can actually see a very unique hole, so you know a caterpillar is in there, but it’s very, very difficult to see. But also, you don’t want to damage the flower head so you have to be very careful. So it’s best to wait the fourth instar to find the fourth instar larva and you can see them below on the outside like this, so they’re fairly easy to see.
Now I’m going to come back to the recovery plan again; remind you the place to look here is the Southam Bypass. So, what do we want to do with a small blue recovery? We want to reestablish a viable metapopulation; that connected series of colonies. And so we targeted the Southam Bypass to start off with. This is just an extract from a report in a book I wrote about small blue. And you can see here it’s a normal bypass; it’s got slopes going down to the road.
And what we did from funding, we had funding to buy some kidney vetch plugs, and so we planted them at the top of the embankment’s both sides. And again, if you’re doing a conservation work, often funding is short and this is a good way of getting the most for the money you’ve got. Because what you hope is, you plant the plug plants at the top of the embankments and over years, they’ll flower, they’ll seed and spread all over the embankment.
And you can see here by year three, the kidney vetch plants are getting large and they’re spreading down the embankment. By year five, they’re covering both embankments and dutifully, once they got to this stage, the small blue colonise the Southam Bypass North.
But one warning about plug plants. This is another site, Ufton Fields, the Ridges, and what we did one day with volunteers is plant 2,000 plug plants all over these ridges which we formally removed of scrub and poisoned the stumps. And if you look carefully, there’s little bits of black all over. On the same night we planted the plug plants, a family of badgers had come along and dug out every single one. And so when we got there in the afternoon, they were all dead. So we basically wasted our time. Consequently, we prefer seeding nowadays.
This is the southern part of the Southam Bypass. Now, this is one of those sites you can say is a really important potential site and I always advocate looking for areas like this. Unfortunately, I haven’t got a before photograph, but I get you to imagine, this area was totally covered in scrub. There wasn’t a blade of grass there. So the first thing we had to do was remove all the scrub and poison it to get rid of it so it wouldn’t come back. And if you look carefully also, just about here and up here, you’ll see what we call permanent compost heaps; it’s another good management practice because that creates habitat for things like slow worms and hedgehogs, so we don’t just conserve butterflies in Warwickshire.
And when we’re conserving grasslands and annual cuts, we like scruffy and I always think this is a good picture of scruffy grasslands. An important thing here is we’ve got areas here where you can have all sorts of invertebrates overwintering, but importantly, this is a site where the small blue can overnight roost.
As I say, one of the most important things about conservation for the small blue, certainly in Warwickshire, is scrub clearance. And again, I’d advocate, you’ve got to be bold. So this is the start of the work before and after, at a place called Harbury Spoilbank North. And you can see here before and the after, you can see that we’ve cleared quite a lot of scrub. But this is small potatoes really, you want to go big, and it’s just two photographs of the site, when we finished our work, and you can see here all the top now has been removed to scrub with a couple of scrub islands (another good management technique), you’ve got your permanent compost heaps here, and this is where you can plant kidney vetch. Now is that slope from a different angle you saw earlier with wonderful ant hills. Now, we’re very proud of this site – it’s one of the sites we look after in Butterfly Conservation Warwickshire – we’re proud of it because it’s got short turf species like the grizzled and dingy skipper, it’s got medium turf species like the small blue and green hairstreak, and it’s also got long turf species like the dark green fritillary and all are doing well on this site. We know that because of the transect that’s walked there. And it’s all done by cutting, no grazing involved, because unfortunately we can’t get grazing on there to help us.
So I mentioned earlier or several times that we now preferred seeding. It’s an easy technique. When you’ve cleared a site, you get lots and lots of bare ground underneath the scrub and all you have to do is use a trowel, you make a scrape sort of horizontally along and you drop about a dozen to 20 seeds down. If I’d criticise this photograph, it’s got far too many seeds in and, again, it’s important in conservation to learn what you do need to do and what you don’t need to do. And here, this is a definite, we put too many seeds down.
And so stage one of restoring your site is always scrub clearance and, volunteers, who doesn’t like a fire? So we clear the site, but what I want you to look at here is the amount of bare ground. And so imagine walking up this slope here in sort of lines parallel to the top and you go along every couple of meters, you stop, do a scrape and you put several kidney vetch seeds down. And that’s what it can look like in one year: masses and masses of kidney vetch. So seeding works really well. And also because this site hadn’t had scrub long, there was a seed bank there. So it’s got other lovely plants like the oxide daisy, common spotted orchids and all sorts of things.
The next technique we developed in Warwickshire was assessing sites and we assess sites not by dropping a random quadrat in the field and saying, oh, yes, there’s all the plates, we look for how many egg laying opportunities there are for a particular species of what we want to improve. And you might be looking there saying, what the hell is an egg laying opportunity? I’ll just go through it. So this slide is about counting the egg laying opportunities for a grizzled skipper.
Now, all these plants here of creeping cinquefoil, the leaves of it are useless; they’re too cold. They’re too… around the grass it always cools the environment. Here, we’ve got a small leaf, and that’s too small for a female grizzled skipper to land on, curl it’s abdomen round and lay an egg. But here we have the Goldilocks leaf; it’s flat against that lump of concrete. And so you get radiated heat from that concrete on the underside of the leaf and makes it perfect for laying an egg.
Now, if you put a laser thermometer down here and you put the laser thermometer down here by this leaf at midday near the end of May, early June, there’d be a 10 degree Celsius difference in temperature. So if you’re a butterfly on the edge of its range, you always pick the warmest spot to lay your eggs. So this gives us an opportunity to actually manipulate habitat.
And so another invention came up in Warwickshire was the butterfly bank. And this gives you a clue. If you look at the top slide here, this is a Butterfly Bank at Southam Quarry. And I can tell you, because I’ve surveyed it, there are as many egg laying opportunities in this butterfly bank, for the small blue, the grizzled skipper and dingy skipper, than the whole of this site put together and how many times have we been to sites and we’ve seen rare butterflies in very, very low numbers spread over the site. Well, this is a method you can reverse that, get them all into a small area. And to reinforce that, this is another site of another butterfly bank at Wrightwood Meadows, and again, this is aimed at grizzled skipper, but if you look at that, the wild strawberry, how many egg laying sites are there for the grizzled skipper? Now, a very, very small area, you’re talking about probably a square metre, probably hundreds. And again, for the dingy skipper, hundreds of egg laying opportunities there where the runners of the common birds foot trefoil run over this type-2 aggregate.
So, you can manipulate habitat for the benefit of butterflies. Also, with butterfly banks, you can put in these poles here, these tanalised poles, you can drill holes north, south, east and west, all up and down the pole and that creates brilliant habitat for solitary bees. So you don’t just have to conserve one species when you’ve got a target species like the small blue to conserve.
Hopefully most of you know, Butterfly Conservation like science, so we did some science experiments at Southam Quarry. This is where we made four butterfly banks. Now, this is an old wheat field, very enriched, so what we did with the first one was we just used the soil from the field, banked it up in a c shape to make a butterfly bank and left it. Then we did another butterfly bank where we just earthed the soil again up there. But this time we seeded it with kidney vetch. Third bank we did was we brought in Blue Lias Jurassic clay and again, we just left that as a butterfly bank. The fourth one, again, we brought in the Blue Lias Jurassic clay but this time we seeded it with kidney vetch. And probably no one who’s been involved in practical conservation will be surprised by this but only one of those butterfly banks worked: the Jurassic clay which was seeded because there was no seed bank in the rest. So again, it’s useful to have this information with you if you’re talking to site owners to say, no, that won’t work or this will; you’ve got to do it.
Another thing we tried at Southam Quarry was the creation of scrapes and this had reasonable success. So we’ve talked about the difficulties kidney vetch has in our modern environment, so what we did here was we seeded kidney vetch down at the base of this scrape on a slope, and it did flower, it did spread all over, but didn’t work as well as we wanted it to. But when we combined it with a butterfly bank, so now in front of the sea of the butterfly bank we make a scrape, it does work really well. So again, combining both techniques works really well.
Another thing I’d advocate looking for and using is yellow rattle; that’s a hemiparasite of grasses, it weakens the grasses. And when you’ve got that in the sward, it creates more gaps in the sword for wildflowers to fall to the ground and germinate. So sometimes you have to look at sites, and it’s not every site, but you have to use yellow rattle to help your conservation work.
So we’ve done all this in Warwickshire. Has it worked? Well, these are the six sites which were occurring in 1999. And here we have the two sites actually Bishop’s Bowl and Bishop’s Hill. The next one here, just above it is Ufton Fields. Then we’ve got Southam Quarry. And these two dots here are Stockton Quarry, which actually covers two tetrads, but there’s just six colonies there in 1999. Don’t forget some of these went extinct by 2009 when we started the recovery program, so we only had three colonies by the time 2009 came around.
Well, our works work pretty well. So we’ve now restored in Warwickshire the 1970 distribution in small blue. You’re seeing in a lot of conservation reports, the first thing it says is restore the whatever species you’re looking after back to its 1970 level. We’ve done that in Warwickshire. But we’ve gone further now: we’ve got a functioning meta population just here, all around the Southam area. And now we’ve managed to get colonies now in the rest of the rest of the Outer Cotswolds area here. And also it goes all the way up to Rugby. So the next 10, 20 years, what we aim to do, you spread all these dots all over here and all up to there and you hope to get at least 60 colonies, maybe 70, in Warwickshire in the next 10 to 20 years. And I think it’s very doable from what we’ve learned from restoring the first part of the landscape.
If you’re wondering about this colony here, we have to thank the Upper Thames branch or Oxford in particular, because they’ve got some colonies just south of us, and this dot down there is where it’s colonized a new quarry on the southernmost part of Warwickshire.
So that’s how we dealt with the small blue in Warwickshire and that’s how we’ve still got work ahead. So I hope you enjoyed the talk. Thank you very much.
Liz Peel [32:50 – 33:42]
Thank you, Mike. That was really interesting. I don’t have a huge number of questions in the chat, there’s just one. If it’s okay, we’ll read that one out first and see if we get an answer. And then if anybody else wants to… I will find it quite difficult to see everyone because we have over 80 people on the meeting. So if you do have a question and you are happy to use the chat that will make it easier for us to manage the questions. I will try and flick through all the names but there’s a lot of you. So if you could put it in the chat that would be great.
So the first question is from Tara and she says, why are some butterflies so fussy about where they lay their eggs?
Mike Slater [33:42 – 34:33]
The main reason is because most of them have northern climatic limits of their range and unfortunately, in the UK, most of our species fall into that category. It’s noticeable if you look back in history, when species fluctuate wildly, we’ve had several species from the extinct black veined white to the comma that’s fluctuated wildly in its range and unless it changes its caterpillar food plant always fluctuates wildly because it’s always vulnerable to extinction.
So things like the grizzled skipper, for instance, of that slide I showed you, hasn’t got the same problem in southern France. And it uses a much more wider range of habitats and cooler habitat. Well, not cooler, but longer turf habitats.
Liz Peel [34:35 – 34:48]
I see. We have a question here, but it’s a very practical one. Where can we get kidney vetch seed from? Where’s the best place to buy it?
Mike Slater [34:46 – 36:06]
Well, the great thing in the last 10 or so years is lots of places have now started growing wildflower seed. So, in the first instance, there’s a place called Emorsgate Seeds in Norfolk, now, it’s not cheap, but as I say, when I travel around Warwickshire I normally have a kilo of kidney vetch and do gorilla seeding as I travel, but they will send kidney vetch to you. But what I’d advocate is if you have a small amount of kidney vetch, you buy it from somewhere like Emorsgate, the great thing about them is it’s got good local provenance so you know it’s local UK seed, and you’ve got people in your branch that are gardeners, it’s great they can grow the kidney vetch on and then you’ll get masses of seed, not only for the current year, but in future years. And that’s a great way of sustainably getting your kidney vetch seed or other plants like common bird’s foot trefoil. It’s a nice cooperative approach. Especially volunteers, because some volunteers don’t feel they can help us and some of them, they say, I can’t help you because of age or disability or whatever it is, but a lot of them are keen gardeners, so you’ve got a greenhouse, can you grow this one? They say, yes and so suddenly they feel they’re contributing to conservation and now I’m getting my kidney vetch basically free gratis so that’s good.
Liz Peel [36:07 – 36:18]
Sounds like a win-win situation. So, Jane would like to know, are the caterpillars fluorescent in UV light, like the holly blue caterpillars?
Mike Slater [36:18 – 36:33]
Yes, they are. In fact, you’ll find, well, I haven’t found a species yet in the UK that’s caterpillars don’ fluoresce in ultraviolet light, but you know, the eggs don’t but the caterpillars and the chrysalises do.
Liz Peel [36:34 – 36:48]
And Nancy says they have common blue in their wildflower meadow, so would they improve with the same kidney vetch improvements and do they also like warm conditions right on the coast?
Mike Slater [36:48 – 37:38]
Yeah, it’s funny, I’ve done a lot of egg searching for the common blue and again, though it’s less fussy, and it obviously occurs all over the UK, it does prefer drier, warmer habitat, and that’s very noticeable. So, for instance, if you constructed a butterfly bank it would be very noticeable that the small blue would use that, especially with climate change, it will use it when we have these cool wet summers, sorry springs.
It’s actually interesting because we’ve got the dingy skipper, yeah, you’ve got the dingy skipper in Scotland but where we’ve got both species, the dingy skipper and the common blue, both use common bird’s foot trefoil, but not the same parts of the plants. So while they don’t compete against each other, there is a slight overlap.
Liz Peel [37:40 – 37:49]
The next question is: has there been a change in the distance they’re willing or able to travel to start a new colony?
Mike Slater [37:49 – 39:10]
That’s a really good question because, again, though I gave the figure of three to five kilometres where they’ll colonise, it also depends on the weather so there’s a rule, if the butterfly is in a big colony and it’s had a good year, first of all, the females get messed about by the male butterflies, so they get pestered, as we say, and they don’t like that, so they tend to try and move away from the males. And also, if you think about it, when they start the egg laying, there’s only limited places they can egg lay. So they thought, well, good year, good population, I think I’ll try and move away and suddenly they start, we think, to smell out things like kidney vetch. And that’s the trigger for them moving away.
Whereas in poor years or when the population’s at the low end, there’s certainly evidence that there’s less likelihood of them colonising sites. So the rule is for colonisation, what you need is a vacant site, large vacant site, with lots of habitat next to a colony which is very very large and virtually, if it’s less than a kilometre away, whatever species you’re talking about, it will get colonised and then as you move further away and the habitat becomes smaller, there’s less chance of it colonising.
Liz Peel [39:10 – 39:22]
Here’s another good question for you. Andy’s asking how the small blue can typically sustain two broods a year when the kidney vetch presumably has only a relatively brief flowering period.
Mike Slater [39:22 – 41:41]
That’s a cracking question because even though it has two broods, what you find is for the second brood there’s far less flower of the kidney vetch about. I don’t really know the answer to this one, but if you do go in southern Europe what you find is a lot of these where we have either single or double broods, say in southern Spain, it’s multi-brooded, it just keeps breeding all year round. And so do the flowers keep emerging, you know every so often they’ll have a real run on flowering and so you get some splash of say kidney vetch six weeks after the first lot. So as we move further north, you get second brood, you’ll get less flowers but you’ll also get a smaller second brood.
And as for advantages in sort of evolution terms, my best guess would be that if it can have more broods, as our weather is our fickle, it can then be better adapted and be better prepared for the next year, so it has another chance to get some eggs and caterpillars and adults ready for the next year. And for certain species, of course, I had the ability to go through two years without produced adults, that was noticeable with the large blue butterfly, they found it could go through two years before producing adults. So there’s some environmental adaptation there, evolutionary thing, that’s going on, but I think, in principle, having a second brood is advantageous, don’t quite know why. And what we’re finding certainly in the Midlands where we’re the sort of on the brink of climate change, some species are now having second broods that weren’t really known to have second broods, like for instance, the white admiral, not every year and probably about every 10 years, the white abnormal has a second brood in September when there’s very, very little suitable honeysuckle for it as caterpillars, so it’s one to look out for. And I think the advantage of people being in Scotland, of course you all know climate change is moving further north, I think you’re going to experience a lot more of these really interesting things to actually have a look at and examine.
Liz Peel [41:41 – 41:52]
The other Midland counties you mentioned, are they also doing any conservation work that you know of?
Mike Slater [41:45 – 42:42]
I think Warwickshire is doing an awful lot of conservation work and most of the branches do some conservation work. But unfortunately, the way things have gone, as I say, the butterfly is now extinct in the whole of the West Midlands other than Warwickshire, and I think there’s only one or two colonies over in I think Nottinghamshire or Lincolnshire somewhere that way, where the butterfly occurs but it’s really a rare butterfly in our area. But some great work for instance in the East Midlands branch conserving the grizzled skipper, because it’s got very similar habitat to Warwickshire, uses disused railways, which again are normally warm and sheltered which, again, a lot of these small butterflies need.
Liz Peel [42:44 – 42:54]
Have you written any guidance for butterfly banks and scrapes? Is there anything out there that people could look at? If there is we could circulate that.
Mike Slater [40:54 – 43:52]
Yeah, there is a fact sheet I wrote for Butterfly Conservation, but unashamedly I actually, I’ve written a book on butterfly conservation which I think is actually sold out now, so I’ll be persuaded to write a second book on conservation but that won’t be out for a couple of years probably. But yes, there’s certainly a fact sheet out there but, as in most things, the original fact sheet now I’ve drastically amended so the thing I advocate for Butterfly Banks is it always fits into the site and that wasn’t really explicitly said in the fact sheet. And, if you have the opportunity, I always go for a S-shaped Butterfly Bank rather than a flattened C-shape for the butterfly bank. And that’s because, if you can imagine the C shape, there’s far more shelter wherever you are, so the butterfly can just nip over to the other side of the bank and get shelter and get on with its egg laying, if it’s windy in a particular direction.
Liz Peel [43:52 – 43:58]
There’s lots of questions, Mike, I hope you’re okay with this.
Mike Slater [43:48 – 43:59]
Yeah, carry on.
Liz Peel [43:59 – 44:03]
Yeah, why are the coastal colonies surviving if they need warmth?
Mike Slater [44:04 – 44:50]
Ah, right. Now, when I do survey work, I always walk around in a t-shirt; that’s deliberate. Even in Scotland, I would do this. Now, if you walk around the sand dunes in Scotland, as you move say from the prevaling winds coming off the beach and you go into the sand dunes proper and between the sand dunes, I bet anyone would find a sudden jump in temperature. And that’s the same for the butterflies, so that’s where they will be, in those shelter conditions, far warmer than just the other side of the dune. And that’s where they’ll be breeding. And if you don’t believe me, what I say is you look for the eggs, that’s where you’ll find the eggs. I haven’t been to Scotland to do this but I’d stake my mortgage on, that’s where you’d find the eggs.
Liz Peel [44:51 – 44:59]
It sounds like, yeah, I would agree, you definitely notice the temperature difference. You just need to get out the wind slightly and the temperature jumps.
Mike Slater [44:59 – 45:18]
Yeah, that’s it. And also, you imagine as the day goes on, and the sun you know travels over the horizon, some areas will get baked with the sun so they’re really, really great sun traps and the species on the edge of the range, or species on the edge should I say, it’s a great place to lay your eggs.
Liz Peel [45:20 – 45:30]
So, we’ve got a question here about, have you got any tips for clearing thick moss that is smothering the kidney vetch on the sand dunes?
Mike Slater [45:30 – 46:36]
Right, now that indicates to me that there’s, somehow, there’s some damp there. Now, in sand dunes that surprises me because they should be free draining. So just thinking about that, I would say maybe the kidney vetch is growing in the wrong place. It’s a different way of looking at things. Now, what I’d say is, the first thing I’d do is go to that place and see if I can find any small blue eggs. Now, if I couldn’t find these small blue eggs, and it’s got this moss problem, the kidney vetch is definitely growing in the wrong place. That might sound perverse, that happens with a lot of our food plants for butterflies all over the UK.
So my job then would be, well, where to put the kidney vetch? And so I’d take the seed off where it’s growing in the wrong place, and I’d see it elsewhere where it hasn’t got moss. And the great thing about moss is it doesn’t go away, so I’d look for a place where there isn’t moss and that’s where I do my seeding.
Liz Peel [46:35 – 44:49]
There you go, Tracy. That’s your answer. Get collecting that seed. That’s from Tracy, our Species on the Edge officer. So the next question is, can you create the perfect environment anywhere?
Mike Slater [44:50 – 48:31]
Yeah, I love a challenge, so I would say yes. Now, some places need more thought, but I think, you know we’ve got a very hostile environment over there because of agricultural intensification, but I’ve created perfect habits or near perfect habitat, on old wheat fields, oil seed rape fields. And some of it’s taken a long time and you sometimes have to think about it; I’ve been involved with sites where we’ve got a problem with eutrophication, well, we’ve got to get rid of it. There’s various techniques depending on the site. If it’s a flat site, you’ve got to invert the soils and get down to the subsoils, probably a meter down, and you’ve got to deal with that. Now, in the fact sheet, there is a technique that is about getting down to the subsoil. So, just quickly about making a Butterfly Bank, that’s half where the concept came from. You basically get a JCB, dig a big hole, you put all the soil you dig out to one side, then you dig it deeper again because you’re at the subsoil, you put that to one side, then you bury the topsoil, and then you make your Butterfly Bank out of the subsoil you’ve got right at the bottom, and therefore, then you can start, and you face it the right way, obviously south preferably the further north you are – you can do it east – but then you make it in the right shape and you can create the right and perfect habitat for that butterfly. It’s all doable. Trust in conservation.
Liz Peel [48:31 – 48:37]
Tracy’s come back and said that the moss is in the main part of the small blue colony. This is in Scotland. It’s wet in Scotland isn’t it?
Mike Slater [48:37 – 48:43]
Oh. Oh, yeah, yeah, yeah. But is it breeding where the moss is? That’s what I’d say, Tracy.
Liz Peel [48:47]
Yes.
Mike Slater [48:48 – 49:37]
Oh right ok, well if it’s breeding there with moss covered plants, the moss isn’t a problem. Simple as that. If it’s not breeding on where the moss is underneath the plant, then I would say, move the plant, yeah by seeding. So let the butterfly tell you what it needs. So – and that’s why I always love egg searching – go and search and map where the eggs are laid and quite quickly you’ll find out that it’s concentrating in certain areas; whatever species you’re looking at, whatever site you’re looking at, it will always concentrate its eggs in one particular batch. So then the idea is don’t try and counter science, replicate what you found elsewhere and therefore it would be better for the colony and the colony will increase in size.
Tracy Munro [49:39 – 50:02]
Okay, thanks, Mike. Yep. It was up north with the North Coast team, so I don’t know the area as well. It’s not on my East Coast, but there are volunteers who are saying, yeah, where the main small blue colony is on the dune system, more and more moss is coming into it, but it is where they are egg laying and it’s where the largest percentage of the adults are seen in this one particular part of the dune system.
Mike Slater [50:02 – 50:27]
Yeah, you’ve got to be careful, looking where the adults are compared to where the egg laying is. Because adults, they’re very big nectar users and, I’ve made this mistake many times in the past, what you find is ‘Oh, that’s where the main breeding site is because that’s where the adults are’, but even with a small blue, it doesn’t fly far, you might find it’s just around the corner. So I think that needs further investigation.
Tracy Munro [50:27 – 50:38]
Yeah. Yeah, there’s definitely eggs. This is where they egg lay in this bit. Where the moss is beginning to take over.
Mike Slater [50:38 – 51:52]
Okay, so if it’s beginning to take over, where it’s taken over – you’ve got to be really sort of focused with this – if it’s taken over one patch, are the eggs there? If there are, there isn’t a problem. If it’s taken over and there’s fewer eggs, and it’s a growing problem, then you need to take action.
So, just split where it is into little compartments and say, you know, even if you divide it into you know five square kilometre you know patches, if you did that and systematically looked at it and think, right, this year there’s 20 eggs in this patch, oh, hang on it’s gone down to 15 eggs next year and because you’ve done drop disk measurements, the amount of moss has increased, then you’ve got a growing problem and you need to take action. And so if there’s an opportunity to put the kidney vetch elsewhere where there’s no moss, you do it, but if you’re going to, say, control the moss then it might be some really sort of basic micromanagement of actually going in there with mini rakes and raking the moss off so it doesn’t get swamped out the bottom, so the bare ground is there to create the reflective heat for the kidney vetch that’s growing above it.
Tracy Munro [51:53 – 52:00]
Yeah, we think that’s possibly what we’ll do, but maybe do it in experimental strips and monitor it more closely to see what’s happening.
Mike Slater [52:00 – 52:34]
Oh, that would be brilliant. And of course, the other thing is I’d probably advocate is, depending where or, the moss obviously goes and comes, but it might be… Actually use these garden rakes, the metal-headed ones, and actually when the species has finished its sort of life cycle and then, you would have to do some strips so you don’t wipe out the colony, then really scrape back to various intensities areas of where the small blue is breeding to see if you can take them back to how they looked 10, 15 years ago.
Tracy Munro [52:34 – 52:42]
Okay, yeah, brilliant. Thank you. And I hope, Sarah, that you’re listening. She’s on the call too and she’s on the North Coast. So I’ll be sending her out to do that. Thanks very much, Mike.
Mike Slater [52:42 – 52:55]
Well, again, it would make a cracking case study, it might make a cracking case study for my next book, so please keep in contact.
Tracy Munro [52:55 – 52:58]
Yep. Okay. Brilliant. Thank you.
Liz Peel [52:58 – 53:10]
So Sarah’s actually got a question here. She’s saying, how do you keep the kidney vetch on a bank as the fertility builds up?
Mike Slater [53:10 – 54:50]
All right, now, what you find is in most banks, because of wind action etc, the fertility will actually leach out, so it goes down to the bottom of the slope. And so that picture I put of Southam Bypass South, what we initially did was we used, actually, garden rakes and we scraped up all the leaf litter to the bottom of the slope and then we went back and we did a really hard rake of all the soils to try and take as much as we could down to the bottom of the slope. So, all about reducing the fertility, then over the years the natural process of rain and sort of wind and everything else like that will drain any nutrients out from the top, make it run down to the bottom; it’s just a natural process.
So we’ve also found this with butterfly banks, we sometimes use soil which we thought was nutrient poor because we don’t test the soil, which we probably should do but we haven’t got the resources to do it, and we found, when you look at it, you think, why is all that grass coming? It’s because it’s too nutrient rich. So, what you do is, after a few years and you use your things like yellow rattle to help you, the nutrient levels at the top of the bank go down naturally. So that’s part of the process. But certainly as a sort of rule of thumb, if you’ve got a sloping site, always target your resources to the top of the site because that’s normally the most nutrient poor and the bonus is whatever you seed or pug plant at the top will eventually run down to the bottom as the nutrients go and as it spreads out.
Liz Peel [54:51 – 55:18]
Okay, that’s great. So I think, unless I’ve missed a question, there has been quite a lot of discussion in the chat, I think that’s all our questions. Thank you, Mike, that was really interesting and I hope everyone really enjoyed it. I’m going to pass back to Eilidh now just to wind things up. And thank you all for attending. Over to you, Eilidh
Eilidh Ross [55:18 – 57:13]
Thank you, Liz, and thanks, Mike, that was absolutely fascinating. I put together our species fact sheet for the website for the small blue and there’s so much there I didn’t know, so I’m excited to go and add more information to our fact sheet.
So yeah, and also yeah a plug for that sheet if anyone does want to find out more – I will update it. Yes, but I just wanted to say, if you want to learn more about what you can be doing for the small blue butterfly, if you’re in Scotland and in one of our project areas on the East Coast or the North Coast, there is definitely opportunities for you to get stuck in and help our teams so please do get in touch. The email address, sote@nature.scot, I’ll put it in the chat, that’s the sort of overarching email address for the programme and then I can put you in touch with the right people; probably the best way. But I’ll pop some details in the chat here and I’ll also, we’ll do a wee follow-up email after this call and I can send you contact details for local officers as well there if you just want to get straight in touch. So it’s Louise and Sarah up on the North Coast and then Tracy and Caitlin on the East Coast. So they’d be your local officers to get involved, but yeah, very exciting stuff going on. So thanks so much, Mike. And thank you so much, everyone, for coming.
I can see… we’ve had one more, do we have time for one more question, Liz? Someone has fired in a last minute one. From Nat, I’ll just read it out because I’m here, so Nat has asked, it keeps on jumping around though so let me see if I can stop it from jumping. Nat says… sorry, my chat keeps on jumping around because people are now leaving. Can you recommend a plant which Nat can grow in a garden which will support a wide variety of butterflies? They mostly have cabbage white and peacock butterflies.
Mike Slater [57:13 – 58:47]
Yeah, now, all gardens, there’s the basic two plants, if you want to create your own wild spaces like Butterfly Conservation are advocating now, there’s two plants and certainly in Scotland it applies, so the first one is alder buckthorn and I’m not sure how far the brimstone has reached Scotland, but it’s moving further north, so that’s the food plant of the brimstone butterfly. The absolute one which – you said you’ve got large white – is I’d grow garlic mustard, and this is where you can do your own citizen science, if you put garlic mustard in your garden in a sunny place, it will be used. That’s not if, it will be used by the green vein white and the orange tip. Now actually searching for the eggs of both those are relatively easy, it’s a great thing to do with children and grandchildren. But the more garlic mustard you have, the more orange tips you have and you can have your own colony in your own garden. I’ve got one in mine.
Now better than that, if you’re really good and even if you’re a dog walker and things like that, is then when the garlic mustard finishes, is just to rub your hand up the side of it, collect the seed, walk out where you’re going to walk the dog, go down your local hedgerow, kick the soil and throw a bit of seed in there, and you’re spreading the orange tip all over that area. I’m not sure again, I know the orange tip is spread dramatically in Scotland but you can help the spread even more by doing those two simple things and they do work.
Eilidh Ross [58:48 – 59:14]
Thank you, Mike. We’ve also, I think one had got lost in the chat, so I’ll ask you that one as well. And I’ve taken a picture of this one so that I can actually read it this time. So Andy has asked: Guerrilla reintroduction of, for example, marsh fritillary adults where food plant and habitat are already present is controversial. How is this different to introduction of food plant and habitat and waiting for the adults to colonise it?
Mike Slater [59:14 – 01:02:27]
Yeah you’re right there is a lot of controversy. Now, even in Warwickshire we’ve had, I worked out once 50 different people were doing releases of some shape or form in Warwickshire over the years. I mean, some of it was just photographers who would open the window and let swallow tail out because they didn’t have the heart to kill it.
But there are certain people who want to get rare species on their sites. Now, the key thing with marsh fritillary, and probably one of the best known introductions is in Lincolnshire there, Chambers Wood, now, we strongly suspect that has been topped up every year since it’s been there, so it’s really an artificial colony. And where you’ve got species like the marsh fritillary, it’s very similar say to the small tortoise shell, it’s very easy to breed and therefore very easy to introduce to a site. But latest research on marsh fritillary basically states it needs a metapopulation structure to survive. So it’s not a species you should be looking at to introduce to a single site. So, I think the latest figures is you’d need probably a hundred hectares, sorry, 100 hectares… it’s a very large area to sustain a marsh fritillary colony. Now, interestingly enough, and this has actually benefited Scotland, there was a reintroduction of marsh fritillary into Cumbria where it went extinct. And because there was a meta population both in Cumbria and just over the border into Dumfries and Galloway, I think the last figures I got was there was now 32 colonies in Cumbria and two or three in Dumfries and Galloway. So that was a targeted introduction of a rare species, the marsh fritillary, but very much into the right landscape, and I’ll stress, landscape.
So there’s lots of little patches of devils bit scabious – its food plant – in a large area. So if somebody’s thinking about what to do, now the first thing you’ve got to do is map all the habitats around so it’s not just one field with devils bit scabious, you’ve got to look at the whole landscape and I would suggest at a minimum like you saw in the work for the small blue because it doesn’t always work, you should look for a minimum of 20 sites with good quality habitat, preferably about 30. And then you put in a request to actually do a proper reintroduction and there’s enough expertise in Scotland to say, well, let’s have a look at this and do it properly. And the thing is because you’ve got the power of Butterfly Conservation behind you, you’re virtually guaranteed it will be a success, but not a success on one site, a success at several sites. So it’s well worth doing. And because things like the marsh fritillary are so rare, it’s got to be worth doing if you know of, if you’re talking about 30 sites in an area where it currently is because it’s gone extinct for whatever reason, then yeah, I’m very much proactive and would support something like that, I’m not speaking for BC but you know it’s got to be sort of 20, 30 sites in a very close area to do it.
Eilidh Ross [01:02:34 – END]
Thank you, Mike. I’m just having a wee look at the chat and I think people are leaving great comments, but I can’t see any more questions amongst this.
So yeah, that’s all been fascinating and nice to get these wee tips from other people as well.
Cool. Okay. I think we’re probably good then. Thank you so much everyone for coming and thank you, Mike. Perfect. Okay. Well, I think we can probably leave that there then. We’ve got another talk. I should really have the date up in front of me. If you give me two seconds, I can get that up. So our next talk, I know it’s in March, yeah, 11th of March, that one will be on the plantain leaf beetle. So quite a rare little beetle. I think you can only get it in Shetland and Orkney and potentially the north coast. We’re having a wee search for it. So yeah, feel free to join us in the 11th of March for that talk.
But yes, feel free to explore the Species on the Edge website for all our upcoming events, opportunities, volunteering opportunities, there’s lots there, or find out more about our species. But yeah thanks Mike so much and everyone enjoy the rest of your evening. Thank you, Liz, as well. Okay. See ya. Bye.
