Male holly blues have sky-blue upper wings with narrow, black borders, whereas females have broad, dull black borders. In both sexes the under wings are palest blue, almost white, with black spots. It is relatively common in the south and Midlands.
The caterpillars are usually green, but some may be camouflaged with pinky stripes. Caterpillars are often easy to find as they leave conspicuous holes where they have munched the flower buds. The species overwinters as a chrysalis, with adults emerging in April.
Adults drink oozing sap, aphid honeydew and carrion juices. Caterpillars usually eat holly and ivy, but also dogwood, spindle and heathers.
The butterfly is generally seen high near the tops of bushes, basking in sunshine with shut wings. Caterpillars on holly and ivy flower buds. Also in parks, hedgerows, woods.