A delicate holly-lover with some unsavoury tastes. Find the holly blue on its foodplant in woodland, or feeding on juices from rotting fruit or carrion.
Common name: holly blue
Scientific name: Celastrina argiolus
Family: Lycaenidae
Habitat: woodland, parks and gardens
Caterpillar foodplant: holly and ivy flower buds
Predators: birds, spiders
Origin: native
Caterpillars: small and green with pinkish marks.
Adults: the holly blue is a small butterfly, light silver blue in colour with black borders to the upper wing which are more defined in females. It can be distinguished from other blue butterflies by the black speckles on the underside of its wings.
Wingspan: 30mm
Credit: Ian Redding / Alamy Stock Photo
Caterpillars: feed on the flower buds of holly and ivy. The larvae bore into the side of the bud and eat the contents.
Adults: feed on nectar, tree sap and juice from rotting fruit and carrion.
Depending on temperatures and location, the holly blue can have between one and three broods in a year. Females lay small, flat white eggs on foodplants.
The hatched caterpillar goes through several moults before it leaves the foodplant to pupate close to the ground, where it turns a light mauve. Those that pupate in spring emerge after a few weeks but the later brood overwinters as pupae.
Credit: Ian Redding / Alamy Stock Photo
Holly blues can be seen in woods, parks and gardens in England, Wales and Northern Ireland, but are not frequent in Scotland. Yearly numbers fluctuate but they are increasingly common.
The holly blue is the national butterfly of Finland.
Spot them from April around holly bushes where the first brood are born and around ivy in the late spring where the second brood are born.
Credit: Papilio / Alamy Stock Photo
The holly blue is not currently threatened, in fact numbers have increased significantly since the 1970s, with the species becoming more widespread.
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