Holly Blue

Towards the end of July, a second brood holly blue butterfly (Celastrina argiolus) was spotted in the reserve and photographed by Clive Knight.

The holly blue overwinters as a chrysalis and the first generation of adults emerges very early in the spring, always the first of the year’s blues, sometimes the year’s first butterflies of any kind. The females, which seem to be attracted to shiny leaves, lay their eggs on holly and the caterpillars feed through the early summer on the young holly flower buds. These are the larvae from which the second brood of adults emerge in July and August.

It is the underwing of the holly blue [1] & [2] that distinguishes it from the common blue (Polyommatus icarus) [3] & [4]

Instead of holly, which is no longer in flower, this second generation of females lay their eggs on the shiny leaves of ivy and the caterpillars feed through the late summer on ivy flower buds. These are the larvae that will pupate in the autumn and spend next winter as a chrysalis, on or near the ground.

The caterpillars of all the blue butterfly family develop symbiotic relationships with ants. The caterpillars secrete a sweet, honeydew-like substance that the ants collect and feed to their larvae. The caterpillar does this in exchange for protection; the ants guard their free food source from predators and, in particular, from the parasitic wasps which lay their eggs inside holly blue caterpillars, co-opting their victims’ metabolism to feed their own larvae.

The reserve is full of dramatic stories and complex inter-species relationships.

Header image: Holly blue female by Gail Hampshire (CC BY 2.0) via Wikimedia Commons

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