May 2011 - The Life Cycle Of The Brimstone Butterfly

Brimstone butterfly - taken by Lin at the UEA   May 2011

This April I have seen many medium-large yellow brimstone butterflies flying around and about Bawburgh, including our garden. When they settle you can see their leaf-shaped, strongly veined, wings which are almost always closed as they drink the nectar from spring flowers, such as bluebell, cowslip, dandelion and primrose. Males have the stronger sulphur-yellow colour while the females seem almost white in flight, and a subtle pale yellow-green colour when settled. These early spring butterflies are ones which have hibernated over the winter.

Male brimstones are the first to come out of hibernation, and they avidly patrol an area looking a mate. When a male finds a virgin female, they fly high into the air together in courtship, before finally coming down to bushes to mate.  The females lay pale green eggs on the undersides of buckthorn and alder buckthorn leaves. If the leaves havenít opened yet they will be laid on twigs or leaf buds. Although several eggs may be found together, this is either the result of different females using the same location to lay eggs or the same female revisiting the same spot at different times to lay more eggs.  During the 10 or so days later, prior to hatching, the eggs change to a darker colour and then finally to grey.

The caterpillars are bluish-green in colour with a pale line low down each side and once they emerge they avidly feed on the leaves of the buckthorns. When at rest the caterpillars have a curious habit of lifting the front half of their bodies off the leaf. After a month the caterpillars pupate away from the food plant. The pupa, resembling a curled leaf, is secured by a silk girdle under a leaf or plant stem. The butterflies emerge about 2 weeks later.

It is now August time and this will be the second flush of brimstones which are seen throughout the year. These brimstones need to feed on nectar rich plants to build up the fat reserves which will see them through the winter hibernation. They show a preference to purple flowers, such as thistle and buddleia but will drink from any nectar rich flower. The long proboscis of this species allows the butterfly to take nectar from flowers such as the teasel, which is beyond the reach of many other butterfly species. They hibernate in the autumn, often among leaves of ivy, holly or bramble.

 Brimstones are not considered an Ďat riskí species, so hopefully we will be able to enjoy their beauty for many years to come.

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