With a 3cm wingspan and sky blue upper wings bordered in black (narrow borders in males and broad borders in females), the Holly Blue is one of the most distinctive of the so-called 'blues'. The underwings are a very pale ivory-blue with black spots. The spring-emerging adults fly in April, May and June and are commonly seen in scrubby grasslands, woodland edges and parks.
The Holly Blue's common name arose because in springtime the female butterflies lay eggs at the base of flower buds on Holly trees and bushes. The emerging catterpillars munch distinctive holes in the leaves of a range of plants including Holly, Heather, Dogwood and Spindle.
The Holly Blue is widespread and fairly common in central and southern England and in Ireland and Wales, but it is scarce (but apparently on the increase) in the north of England and only occurs as an occasional vagrant in parts of Scotland. Elsewhere this pretty little butterfly is common and widespread across most of Europe, from northern Scandinavia down to the Mediterranean. The Holly Blue's range extends down into North Africa, and it is also recorded from parts of Asia and from North America.
Eggs are laid singly at the base of Holly buds, and the green catterpillars (often with pinkish-brown markings) grow to a length of 1.2cm within three weeks; they then pupate as brown crysalises some 9mm in length attached to a leaf or a stem. Adults emerge in spring within typically two to three weeks, depending on temperature. In Britain and Ireland there is also a summer brood that can be seen on the wing from late June to early October. This butterfly overwinters in its pupal state.
This page includes pictures kindly contributed by Simon Harding.