Small blue butterfly

Cupido minimus

Key facts

Gaelic name: An gorman-beag
Wingspan: 18 – 27mm
Distribution in UK: South-central England, east Scottish coast, south coast of Wales and the east and west coast of Ireland.
When to see adults: May – August
Status: UK BAP Priority Species
Species on the Edge areas: East Coast; North Coast

Species information

How to identify

The small blue is the UK’s smallest butterfly with a wingspan of 18-25mm. Male small blues tend to be dark grey black with a hint of silvery/blue scales at the base of wings. Females are much browner in colour with no sign of blue. Their underwings are silver-blue dotted with black.

Lifecycle

Egg: mid May – mid July

Caterpillar: mid June – late April

Pupa: mid April – late May

Adult: mid May – early July

Distribution

In the UK the small blue butterfly can mainly be found in south-central England, but it can also be found on some eastern Scottish coasts, the south coast of Wales and the east and west coast of Ireland.

Small blue distribution map (c) Butterfly Conservation https://butterfly-conservation.org/butterflies/small-blue

Habitat and feeding

The small blue relies on grassland habitats that provide shelter for the adults and early successional conditions where kidney vetch – the sole foodplant of the small blue butterfly – can flourish. In Scotland most colonies are found on steep coastal grasslands and sand dunes but some colonies occur on man-made habitats including quarries, disused railway lines and tracksides

The caterpillar’s sole food plant is kidney vetch (Anthyllis vulneraria). Both sexes nectar on various flowers including common bird’s-foot-trefoil (Lotus corniculatus), kidney vetch and horseshoe vetch (Hippocrepis comosa). Males will also take salt and minerals from damp mud and animal droppings.

Conservation status

Protected in the UK under the Wildlife and Countryside Act, 1981.
Priority Species under the UK Post-2010 Biodiversity Framework.

Threats

The small blue is under threat from the increasing isolation of populations due to its reliance on kidney vetch, an early successional plant. Early successional plants are the first to grow in areas of disturbed ground, low in nutrients. As time passes and nutrient levels rise the kidney vetch is lost and replaced by more vigorous plants. Restoring connections between colonies is therefore vital for the long-term conservation of this species.

What Species on the Edge is doing

Increased monitoring and surveying, to better understand the species’s needs at all stages of the lifecycle
Raising awareness among landowners and the public of the butterfly
Working with landowners to better improve connectivity and quality of habitat