Small Blue (Cupido minimus) reintroduction to South West Scotland

Pair of Small Blues mating on Kidney Vetch

The Small Blue is the UK’s smallest butterfly (wingspan 16-27 mm). Colonies of this charming little butterfly can be found from the north of Scotland down to the south of England, but became extinct in south west Scotland in the early 1980s. In 2007 it was added to the UK Biological Action Plan (BAP) species list after suffering a significant decline in distribution.

The butterfly’s small size and weak flight mean that the adults are quite sedentary, with few individuals moving further than 50 m from the colony during their short lives. Both sexes are similar with dark slate blue upper wings and silvery blue undersides with a few dark spots. Males often have a dusting of blue scales on the upper-wings, while the females tend to be slightly browner than the males. In Scotland, adults can be on the wing from late May/early June through to July, depending on weather conditions. A small second brood may be seen in August/September in exceptional years.

The female lays a single egg on the flower heads of kidney vetch, the caterpillar food plant. Only one egg tends to be laid per plant as the young caterpillars can be cannibalistic. When not being anti-social the caterpillar feeds on developing seeds in the flower head, undergoing 3 moults before hibernating under moss or in a crevice in the soil. The following spring the caterpillar pupates without further feeding. Adults seem to prefer nectaring on the yellow flowers of kidney vetch or birds-foot trefoil, although other plants may be used.

Kidney Vetch flower colour forms


Colonies of this butterfly tend to be small and are prone to local extinctions due to their dependence on the levels of kidney vetch flowering in the colony area. Habitat fragmentation and loss due to building developments, changes in grazing and scrub encroachment, can all quickly make sites unsuitable for this habitat specialist species. Most colonies are found at coastal locations where erosion exposes bare ground where new kidney vetch seedlings can germinate and the adults can bask in the sun. Colonies may also be found at old industrial brown field sites or quarries; again with lots of bare ground and low fertility where the kidney vetch does not get out-competed by grasses. Low levels of grazing by rabbits can help maintain small blue colonies; however they do tend to eat the flower heads, as do sheep. Autumn /winter grazing and ground disturbance by cattle or horses is ideal at managed sites.

Map of Gailes Marsh


The Glasgow & South West Scotland Branch of Butterfly Conservation together with the Scottish Wildlife Trust would like to reintroduce this charming little butterfly to south west Scotland. Gailes Marsh is an SWT nature reserve situated just south of Irvine on the Ayrshire coast, and just 1km from the site of Ayrshire’s last small blue record.

The reserve currently boasts a range of butterfly and moth species including common blues, small coppers and dark green fritillaries. An area with a high density of kidney vetch exists in the south west of the reserve. We plan to expand this area and also transform the north- west section of the reserve into good small blue habitat. Coastal dunes west of the reserve contain suitable small blue habitat with good amounts of kidney vetch.

It is hoped that we will eventually see natural colonisation of this area by butterflies from the reserve.

The timing of the actual reintroduction will depend on how long it takes to create good quality habitat and maintain the levels of kidney vetch flowering on the reserve, which must be sufficiently high to support a healthy butterfly population. Kidney vetch is a short lived perennial which can take between 2-5 years to flower depending on conditions. We are currently in discussion with other branches of Butterfly Conservation about the source of initial small blue stock for the project.

Habitat creation at Gailes Marsh is due to commence in early 2010. The fertile top soil will be removed to create strips of bare sandy subsoil and south-facing soil banks that will be sown with kidney vetch seed. The areas sown with kidney vetch will be sheltered from the wind by planting native hedging along the western edge of the reserve. The first conservation work day at Gailes Marsh will take place on Saturday the 20th of March. Please get intouch if you'd like to come along and help.

Small Blue Buttefly on Kidney Vetch

Anyone who would like to help with this project would be very welcome indeed. We are currently looking for volunteers to help create a sheltering hedge (~400 hawthorn plants) and sow kidney vetch. If you are able to find space in your back garden, window sill or green house to grow kidney vetch plants for the project, we can provide you with seed.

In the next few years we will also need volunteers to help monitor kidney vetch germination and flowering at Gailes Marsh and areas outside the reserve. After the small blues are introduced to the reserve we will need volunteers to help with timed counts of adult butterflies during their short flight season. This is necessary to monitor how well the project is going. Training in using a GPS device to accurately monitor kidney vetch patches or butterflies can be provided to any interested volunteers. This is a fantastic opportunity to get involved with real conservation work for a native Scottish species.

Scott Shanks (scottshanks01@msn.com)