The holly blue, which was once known as the azure blue, can be distinguished from the widespread common blue by the lack of any orange dots on the undersides of the wings.
Widespread in the south and spreading northwards. Has recently colonised the Edinburgh area. Less widespread in Northern Ireland, where it is mainly found in the east. It is the most common blue butterfly found in UK woodlands and gardens.
Caterpillars feed mainly on the flower buds and berries of holly, ivy, spindle and dogwood. The adult butterflies feed on aphid ‘honeydew’.
Did you know?
Holly blue populations go through regular cycles of boom and bust, caused by a parasitic wasp. The wasp's young develop inside the butterfly’s caterpillars and pupae, ultimately causing their death. When holly blue caterpillars are abundant, the wasp thrives and kills so many that the population of the butterfly is driven down. However, once at low levels, the wasps find it difficult to locate caterpillars and so its population declines, allowing the butterfly to increase once again.