Sunday, 2 December 2012

A sting in the tail ...

Plaistow, 22 August 2012

Social wasps are among the most familiar and most feared of British insects. In late spring the over-wintered queens sometimes cause alarm as they search for nest sites around our homes and places of work. From late summer onwards their numerous smaller daughters (the workers) commonly cause nuisance and fear to many people. The continuous comings and goings of wasps from under eaves and other sheltered sites betray the presence of a nest. However, these industrious insects have another, beneficial side to their usual stereotyped image. Both queens and workers provide chewed insects and other invertebrates as food for their larvae. Such prey includes many pest species taken from our gardens and agricultural environments. Wasps also visit flowers for nectar and thus play an important role in pollination.

The eight true species of British social wasps all have a similar life-cycle. Nests are built in sheltered sites e.g. in cavities in the ground, in hollow trees or in lofts and outhouses (most colonies of Vespa and Vespula species); or suspended, usually among foliage, from the branches of shrubs and trees (most nests of Dolichovespula species). Each colony is initiated in the spring by an over-wintered queen. She builds a small golf ball sized nest which contains about two dozen cells forming a single layer. In these her first workers are reared. On emerging from their cells as adults, they take over all of the duties formerly performed by their mother, except for egg laying. They add more cells to the circular comb and will build further combs enlarging the outer shell of the nest to accommodate them.

Mature nests of the Common Wasp (Vespula vulgaris) can be very substantial in size: one example recorded by myself had a circumference of just over 2.25m. The population of a colony can often number several thousand in late summer. A nest is constructed from wood fibres (scraped from rotten or weathered timber by the wasp’s mandibles) which are mixed with saliva to form a tough paper. The horizontal, circular combs each contain many hexagonal cells, the openings of which face downwards. It is in these that the brood is reared. From mid-summer onwards new queens and males are reared. Once mated, the queens seek out sheltered sites in which to over-winter. The remaining nest population survives until late summer or autumn, depending on the species. Nests are never re-used and those in open sites soon disintegrate. The Hornet (Vespa crabro) is the largest European social wasp. The spectacular queens can measure up to 50mm in length; males and workers are smaller.

The queens and workers of all species have the ability to sting. Most stings are painful, but generally harmless, and only affect the area around the sting. However, some people can have an immediate, and more widespread allergic reaction to being stung, such as an anaphylactic shock, which can lead to death in some people. This is fortunately quite rare, affecting approximately 3 people in 100, though this is of little consequence to those who suffer in this way. The destruction of an active wasp nest can therefore be extremely hazardous and should only be attempted by professional pest controllers. In general, if a nest does not pose a threat, it is best left alone.

The Hornet (Vespa crabro) at its nest entrance ...


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