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Holly blue butterfly

Holly blue butterfly

Celastrina argiolus

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.


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It is relatively common in the south and Midlands, but more rare farther north: numbers fluctuate from year to year. 

In spring females lay their eggs at the base of flower buds on holly bushes. Later in the year females use ivy bushes, as well as sometimes spindle, dogwood and heathers. 

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. They probably pupate on or near the ground and are likely to be tended by ants. This species overwinters as a chrysalis, with adults emerging in April.

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What does it eat?

Adults drink oozing sap, aphid honeydew and carrion juices. Caterpillars usually eat holly and ivy, but also dogwood, spindle and heathers.

When will I see it?

Adults between April and June then August and September. Caterpillars between May and June then August and September.

Where will I see it?

Generally high up near the tops of bushes. Basking in sunshine with shut wings. Caterpillars on holly and ivy flower buds. Also in parks, hedgerows, woods.


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