Holly Blue Butterfly
We often see Holly Blues flying along the tops of our hedgerows in late spring - they are the earliest of the blue butterflies and the only species to prefer flying high.
The Holly Blue usually has two broods, one in spring and a second in summer.
The adults are easiest to identify when at rest, since their undersides are distinctive and they only tend to open their wings in weak sunshine. The male and female are distinguished by their uppersides, the forewings of the female having broad black borders that are absent in the male. Second brood females generally have broader black borders than first brood females.
The species fluctuates wildly in numbers from year to year in a predictable cycle. This seems to be caused by parasitism from the wasp listrodomus nycthemerus, whose sole host is the Holly Blue. The wasp lays its eggs in Holly Blue larvae, with a single adult wasp eventually emerging from the Holly Blue pupa.
Holly Blue caterpillars feed mainly on the buds, berries and leaves of holly in the spring generation (they prefer female holly bushes) and ivy in the summer generation. Adult butterflies feed on holly, bramble and forget-me-not for nectar, although they seem to prefer honeydew. The males will also come down to the ground to take salts and minerals from damp mud and animal waste.