Saturday, 24 July 2010

White admirals seek out shade

It seems as if the White Admiral butterflies have had a good season across their British range. The hot June weather appears to benefit this delicate woodland species, shortening the time that it spends as a mature caterpillar and chrysalis. This is important, because both of these life cycle stages are prone to predation by hungry birds and the less time they spend going through these phases the more likely they are to reach adulthood and the all-important chance to reproduce.

White Admiral, by Mike Toms

Although easily overlooked, this is one of my favourite butterflies; a truly elegant species when seen in flight and a denizen of shaded mature woodland intersected by warm, sunlit rides. Adult White Admirals spend a lot of time in the canopy, where they bask in the sun and dine on honeydew produced by aphids. Early in the day good numbers may descend to the woodland floor, stopping to nectar on bramble flowers or to sip at water from puddles or the dissolved salts available in animal dung. Dark brown in colour, they are a good size and sport white wing markings that seem to dance through the air as the butterfly moves quickly on short glides and fluttering flight. Many writers have commented on their manoeuvrability and this is certainly evident when you watch the female White Admirals laying their eggs.

Egg-laying takes place on spindly honeysuckle plants, non-flowering and typically located within shade. Each female lays her eggs quickly, curving her abdomen down to deposit a single egg onto the larval food plant. The eggs, which are tiny and best viewed through a hand lens, resemble miniature sea urchins, with their erect bristles and honeycomb exterior. Although the eggs can be tricky to find, the caterpillars are less of a challenge. Each caterpillar will strip back a leaf of the foodplant from each edge, leaving the central rib in place and projecting forward. It is on this rib that the young caterpillar will rest, settling on a mat of faecal pellets and held together with silk. The caterpillars feed up throughout the summer before constructing a shelter for the winter. Again, this uses the leaf of the food plant, trimmed to size and then sewn in place with silk. Here the caterpillar will remain through until the following spring, at which point it will emerge to continue feeding. It is then that the chrysalis is formed; a green, black and silver-jewelled construction that reminds me of a bat, complete with long dark ‘ears’.

Locally, in those woods that support them, the White Admirals are on the wing from mid-June, typically peaking in the third week of July. They are well worth a visit if you can track them down.

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