Blue butterfly numbers reach their peak in June

By Jim Hurley - Nature Trail

Published 09/07/2016 | 00:00

While Common Blue Butterflies are flying at present their numbers are reduced.
While Common Blue Butterflies are flying at present their numbers are reduced.
While Common Blue Butterflies are flying at present their numbers are reduced.

Blue butterflies are on the wing at present and are a pleasure to see especially when flitting about in sand dunes at the seaside.

We have three species of blue butterfly in Ireland, the Common Blue, the Holly Blue and the Small Blue. The Common Blue is by far the most plentiful so it is the one that most people are most likely to see. While Common Blues are flying at present their numbers are reduced. Their numbers peak in June with a lesser peak in August/September and a lesser one again in July.

As shown in the image above, the upper surfaces of the wings of the Common Blue are an intense, bright, shining blue. However, that holds true for the male only and in Ireland only. While Common Blues are found throughout all of Europe, in North Africa and in the Canary Islands, the insects found in Ireland belong to a distinct sub-species that is slightly larger and more brightly coloured than the Common Blues found elsewhere.

The shining blue wings of the male Common Blue are bordered by a thin black line inside a white border that fringes all four wings.

The upper surfaces of the wings of the female Common Blue are a mixture of blues and browns, never all blue like the male. Females do have the same thin black lines and white borders as the males but, in addition, they have a series of black spots and distinct bright orange crescents making them look quite different to the males. Both sexes have orange crescent markings on underside of their wings.

Females lay their eggs on Common Bird's-foot-trefoil and Lesser Trefoil and the small, bright green caterpillars feed on these plants before turning into pupae from which adults emerge.

Caterpillars of the Holly Blue feed on Holly and Ivy so it is more a species of woodland, hedgerows, parks and gardens. The adults are distinguished from Common Blues by their silvery-blue colour tinged with lilac, the presence of black spots on the upper sides of the wings and the absence of orange crescent markings on the undersides of the wings. Their distribution is scattered and are not at all as plentiful as Common Blues.

The final member of the trio, the Small Blue, is tiny and is not really blue. Its colour is described as varying from smoky blue-black to dark bronze-brown. Its main haunts are the Burren in Co Clare, some coastal areas and a few inland eskers.

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