Small Blue

Description:

The Small Blue (Cupido minimus) is a small, native butterfly mainly found in south-central England as well as along the south Welsh coast and the west and east coast of Ireland.  In Scotland the Small Blue is known from the north and east coasts, and the Solway Firth.  On the wing from mid-May to late June, females lay eggs singly into the flower heads of Kidney Vetch. It is common for females to not lay on flowers where an egg is already present as only one caterpillar can mature on a single flower head.

Caterpillars of the Small Blue feed on the developing flowers and from mid-July they can often be seen biting holes in the base of the flowers to get to the seeds.  The caterpillars are cannibalistic and will eat other Small Blue caterpillars if hatched on the same flower, or any smaller larvae they encounter.

The upper side of the Small Blue’s wings in both sexes are a sooty brown in colour, with what appears to be a white fringe around each wing.  The undersides are silvery blue/grey in colour with several white ringed black dots. The males have a light dusting of silvery blue scales located at the base of the upper side of each wing.

Listed as ‘Near Threatened’ in the Red List of British butterflies this species has experienced a 44% decrease in distribution between 1983 – 2019. It is a Scottish Biodiversity List species, considered to be of principal importance for biodiversity conservation in Scotland and in most urgent need of conservation action. The Small Blue is a Section 41 species of principal importance under the NERC Act in England; Listed on Section 7 of the Environment (Wales) Act 2016, Northern Ireland Priority Species; Protected under Schedule 5 of the 1981 Wildlife and Countryside Act (for sale only); Fully protected under the 1985 Northern Ireland Wildlife Order.

• Size: 16-27mm wingspan
• Life span: Annual life cycle; from egg to adult approximately a year.  Adults can live up to 3 months
• Diet: The Small Blue’s sole foodplant is Kidney Vetch (Anthyllis vulneraria). The caterpillars exclusively live in the flower heads where they feed on developing anthers and seed.
• Reproduction: The female Small Blue lays a single egg into the flower heads of Kidney Vetch.  It is common for females to not lay on flowers where an egg is already present as only one caterpillar can mature on a single flower head.  It is a single-brooded species
• When to see:  The Small Blue can emerge at vastly different times of year in the UK, often due to the spring weather affecting development. Emergence of adults is usually from mid-May, peaking in June and finishing by July.
• Population Trend:  Mixed depending on location.  In the latest GB Red List this species is increasing its range.  However, the Small Blue is one of Scotland’s most threatened butterflies, with populations having declined significantly in distribution and size; data suggest a ~44% population decline since the 1970s.  In Northern Ireland they are Near Threatened and listed on the Northern Ireland Priority Species List
• Threats:  Changing land use is the biggest threat to populations. In Scotland, large areas of the east, north and Solway Firth coasts are vitally important for Small Blue butterflies where coastal grasslands, vegetated shingles, dunes and undercliffs provide a rich diversity of habitats. However, a lack of active management such as grazing or scrub control on coastal grassland and slopes continues to threaten the species at sites with encroachment of scrub (e.g. Gorse) and rank vegetation.
• Fun Fact:  The Small Blue is Britain’s smallest butterfly species!
• Additional Fun Fact: The caterpillars are cannibalistic and will eat other Small Blue caterpillars if hatched on the same flower, or any smaller larvae they encounter.

How you can help: 

Buglife is working to increase awareness of invertebrates and the Small Blue through specific projects, like Belfast’s Buzzing and campaigns, but we need your help!

Join a recording scheme and log your finds – send any records/sightings to Butterfly Conservation or download the iRecord app and get recording!

Rockin’ the Blues is a project led by Butterfly Conservation as part of the Species on the Edge project. The project aims to revive the fortunes of the Small Blue butterfly through habitat management at key sites, monitoring populations and habitat condition on the East coast of Scotland.

Do remember that we rely on donations to continue our work.  If you have searched, found and learnt about our incredible invertebrates on our website, please do consider Making a Donation, Becoming a Member or maybe even making a purchase in our shop.  For more ideas on how to support our work find out how to Get Involved.  Thank you 🕷

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