Thursday, June 6, 2013

Orange tips

Today's Guardian Country Diary describes the way in which orange tip butterflies always seem to roost in the open, usually perched on a flower, when bad weather approaches - but always emerge miraculously unscathed after a rain storm has passed.

We've had a colony of orange tips in our garden for over twenty years. Apart from  butterflies that hibernate as adults - peacocks, commas and small tortoiseshells - they are always the first to hatch from overwintered pupae, just at the time when lady's smock Cardamine pratensis comes into flower. This is one of their caterpillars' food plants, but I've also planted the carnation-scented sweet rocket Hesperis matrionalis which they also breed on. The third caterpillar food plant is hedge garlic Alliaria petiolata, which the first female orange tips to emerge usually lay their eggs on. This can be a rather invasive plant if you let it run to seed but the caterpillars consume a substantial proportion of the seed pods.

The eggs are laid singly, either on the inflorescence axis (here on hedge garlic) or on a flower pedicel. They only ever lay one egg per inflorescence, because the caterpillars have cannibalistic tendencies if they have to compete for food.

The green caterpillars (see photo here) align themselves along the developing seed pods of the food plant, eating the pod from the tip towards its base, and in this position can be hard to spot.

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