Monday, 10 April 2017

On the wing: The Orange-tip Butterfly

A.cardamines male
The warm spring here in Bristol has resulted in the emergence of a wide range of butterflies. Overwintering adults that have now left hibernation and are busy looking for mates and egg laying sites that I have seen so far are Peacock, Comma, and Brimstone, and those that overwintered as pupae and are now hatching include Holly Blue, Speckled Wood, and the subject of this post, the Orange-tip Anthocaris cardamines.

A.cardamines female
Orange-tips are one of the most commonly seen of British spring butterflies, outside of the north of Scotland, and are fairly adaptable in their habitat choices. They are not territorial, instead males and females wander widely along lanes and hedgerows. While on the wing their vivid white, with additional orange wing tips in the males, attracts attention from birds but also warns them off. As with many of the Pieridae, they accumulate mustard oils from the larval food plant which renders them distasteful. At rest the black and yellow scales on the hind wing give a mottled green effect which matches the flower heads they rest on.
The Orange-tip female selects the flower heads of various crucifers for egg laying. In Britain the key food plants are Cuckooflower Cardamine pratensis and also Garlic Mustard Alliaria petiolata. The larvae feed on the flowers and developing seed heads. As these are usually only large enough for a single larva the female avoids laying on a seed head which has a recent egg laid by another female, which she detects by the warning pheromone a female leaves behind. If another egg is laid anyway, presumably after the pheromone disperses, the older larva will eat the egg or smaller larva to eliminate competition. Females deliberately select the largest flower heads to improve their chances. Prominent, unshaded plants growing within 1m of a woodland edge or hedgerow are preferred.
Garlic Mustard
The larva is a typical smooth, camouflaged pierid that feeds on the seed heads and pupates around June after leaving the plant for nearby cover. Whilst growing the main threat is probably parasitic wasps and flies. Pupae will succumb to small mammals and birds. Adults are probably immune to birds but will fall to spiders and the like.
The Orange-tip has numerous local subspecies and a vast distribution from Ireland across to Japan. Related species are found in North Africa, such as the Provence Orange-tip A.euphenoides, and there are several North American species as well. All have a similar life history but differ in the preferred crucifers they use as food plants. For example, Felder’s Orange-tip A.cethura from the south western United States feeds on California Mustard Guillahenia lasiophyllia.
(images from Wikimedia)

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