DOLICHO VESPULA MEDIA STATISTICS

Two wasps nests were a built in a Viburnum tomentosum bush in my garden. The larger was first seen on 21 July 2002 as an intensifying drought stripped leaves from the bush and a second, smaller nest became apparent a few days later.

p. ??). They were about 500 mm from the ground and the same distance apart.

Their construction and position identified them as nests of the median wasp, Dolicho vespula media. This was confirmed by Mr. Adrian Knowles to whom I sent a specimen which turned out to be a male median wasp. This is a continental species, now spreading widely in Britain and has been found in Suffolk (Knowles & Lee, 2001).

When first noticed, the wasps were very active, a steady stream flying off foraging while others on the nest surface appeared to be engaged in nest maintenance. At this time the wasps were very aggressive and resented any close approach. By 19 August, however, they were only a few lethargic wasps around the nest, some crawling around the entrance while others rested on nearby leaves reluctant to fly, easy to photograph or to capture for identification. This early demise of the colony was a surprise as ground nesting German wasps in the garden were still very active (as they still are at the end of September).

In both nests there were three combs; those of the larger nest ranged in diameter from 130 mm for the middle comb to 115 mm for the bottom comb (Table). The combs of the smaller nest were smaller and the bottom comb was only 60 mm in diameter. Cell numbers per comb showed similar trends. In the larger nest the diameter of the cells increased from the top to the bottom comb, the larger cells in the bottom comb presumably to accommodate the males and queens (Table).

Within each comb there was no obvious trend in size although in the bottom comb of the large nest, diameter was not normally distributed but was skewed towards the larger diameter, perhaps indicating that variation in cell size within the comb was not random, but that some larger diameter cells were constructed for the queens.

On the continent, median wasp workers fly from the end of May and are still seen after mid October; females appear in the first part of August and males fly from the middle of August to the middle of September (Zahradnik, 2000). Compared with this the Westleton colonies ceased activity very early.

Adrian Knowles, the Aculeate Hymenoptera Recorder suggested that, as a recent continental colonist the median wasp does not like the wet and cold. During the period 21 July to 19 August the minimum air temperature was above 10° C. Grass minimum fell below 10° C on four occasions during August, including 17 August when the grass temperature was 6° C. There were 10 mm of rain in the period 31 July to 2 August, but otherwise the only significant rainfall was on 19 August (5.4 mm). Another possibility to explain the precipitous decline of the colonies was disease or poisoning by garden chemicals although I could find no evidence of this other than the behaviour of the wasps, which may be typical of the species..

Total cell number per nest, particularly of the large nest (Table) appeared to be greater than that reported on the continent. Zahradnik (2000) states 'the number of cells and hatched adults is low. Nests with some hundreds of cells are considered large in Central Europe' and also 'the nest accommodates about 300 - 500 cells' Observations of the life cycle of the median wasp and measurements of its nest may show that the wasp is adapting to the British climate. Changes in the life cycle and nest size are known when wasps colonise a new habitat. An example, albeit somewhat extreme, is the spread of Vespula germanica in Australia. It was first found in Tasmania in 1959 and has since spread widely in the Eastern States. In the warmer climate a new queen may stay in the nest and begin laying eggs, without the usual over-wintering period. Over several seasons this can result in giant nests containing more than 100,000 wasps.

Tables.
Cell and comb dimensions of two Dolicho vespula media wasps nests

Large nest - 150 x 270 mm

Small nest 130 x 180 mm

References

Knowles, A. & Lee, P. (2001) Aculeate Hymenoptera Recorders Annual Report.

Transactions Suffolk Naturalists Society, 37; 92-94

Zahradnik J. (2000) Bees and Wasps. Leicester, Silverdale Books

E. J. M. Kirby,
The Studio, Blythburgh Road, Westleton, Saxmundham, IP17 3AS

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