Wednesday, 17 August 2011

Busy colony occupies roof space

Significant numbers of wasps are entering and leaving the roof-space above the kitchen via a tiny gap under the bargeboard outside. The volume of traffic hints at a busy nest, with numerous workers now mature and able to resource the demands of a nest at its seasonal peak. I don’t begrudge the wasps access to the roof-space, though I know that many people do. It is not as if I use the tiny space for anything other than the storage of a few boxes and pans. My curiosity has, however, prompted me to net one of the wasps in order to identify it; there are a number of similar-looking species in Britain, at least two of which will make their nests in houses and outbuildings.

It turns out that this is a Common Wasp, hardly surprising but worth knowing since the other species I have seen in houses locally (the Tree Wasp) tends to produce much smaller colonies. By comparison, an average-sized Common Wasp nest can produce some 10,000 workers, 1,000 queens and 1,000 males over the course of a season. I guess some readers will be less than impressed with this piece of newly-acquired knowledge.

These wasp colonies are annual affairs, with only the fertilized queens overwintering by seeking shelter in outbuildings, houses, behind bark and, occasionally, under stones. Activity picks up in spring and then gradually builds to a late summer peak, the colony finally collapsing in mid-November (or later if it remains mild). The colonies of Tree Wasps can last even longer. It is the nests that wasps produce that have long-fascinated me. Constructed from wood, which is chewed up to form paper, the domed structure can reach a fair size, holding up to 12,000 cells in which the queen lays her eggs. The resulting larvae are fed on a regurgitated mass of masticated insects and spiders, many of which would be viewed as garden pests by most gardeners. The adults, however, have a diet based around nectar, tree sap and honeydew. It is this preference for sweet things that has brought the species into conflict with us, the wasps arriving to spoil afternoon tea and other meals taken outside.

Wasps don’t have things all their own way though, with a number of other species known to exploit the nests and their larvae. Larvae of the small beetle Metoecus paradoxus, our soul representative of the Ripiphoridae, will invade wasp nests to feed on the developing wasp larvae. One of our hoverflies also rears its larvae in the nests of wasps, this time scavenging some of the waste produced by the colony. Later in the year I will take a look at the nest itself but for now I’ll leave it unmolested.

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