The Common Wasp
Colonisation of Shetland
Mike Pennington, Kevin Osborn
and Dave Okill
Social wasps of the family
Vespidae are only occasionally recorded in Shetland, Britain's most
northerly land mass. Many records are anecdotal but they suggest that
accidental importation, often in fruit, is the most common source of the
records. However, records from ships at sea and from the remoter islands
imply that natural vagrancy may occur. In the latter category are records
of a Norwegian Wasp Dolichovespula norwegica on Fair Isle on 22nd
August 1991 and an unidentified wasp on Foula in June 1992. A German Wasp
Vespula germanica found in fruit at Cunningsburgh in March 1993 was
unusual only in that anyone bothered to identify it. Talking to shop
assistants anywhere in the islands reveals that wasps are amongst the
commonest of the entomological surprises to be found in consignments of
fresh produce.
In
the summer of 1993 both Neil Marks and Harry Rose independently caught
wasps free-flying in Lerwick which they identified as Common Wasps
Vespula vulgaris. In September however the Shetland Islands Council
(SIC) Environmental Services Department was notified of an active wasps
nest in Kveldsro Gardens, in central Lerwick. The nest was causing concern
to the residents and required removal. Upon investigation the nest was
found to be in the roof cavity of a single storey house. The nest itself
was inaccessible and it transpired that the nest had been active since
early summer and was supporting a healthy colony, as up to 20 individuals
were being killed each day. A few specimens obtained were identified as
V. vulgaris and a specimen from this nest has been placed in the
National Museum of Scotland in Edinburgh. The nest was treated with
insecticide, but as it was nearing the end of it's breeding cycle it was
thought unlikely to have much effect. Wasps, presumably from this colony,
caused quite a nuisance in the shops of Commercial Street in central
Lerwick in the autumn, where their unfamiliarity caused some
consternation.
At
the time it was thought that this was the first proven breeding record of
wasps in Shetland but in discussion with employees of the SIC Housing
Department it was revealed that they had removed an entire nest from a
house at Sound on the outskirts of Lerwick in 1989. No specimens from this
nest were retained but is believed that they were also Common Wasps.
In
1994 adult wasps were noted around Lerwick from late July onwards. The
presence of nests was not confirmed until 28th August when one was
reported from Knab Road, close to the location of the previous years nest.
Thereafter followed several reports of other nests, primarily as a result
of the SIC requesting details of the location of any nests in the local
newspaper. A total of 18 nests were discovered in Lerwick including one at
the previous year's site. Ten nests were within a few hundred metres of
the original site and seven more were strung out in an almost straight
line up to a kilometre away. The remaining site was at Helendale on the
far side of Lerwick, almost 2 km distant. Located nests included eight
situated in roof or floor spaces in buildings and ten in the ground.
In
addition there were several reports of Common Wasps entering houses in
Scalloway (8 km to the west of Lerwick) in 1994, suggesting at least one
nest was in that area, but despite several requests for information on
nest locations, none were found until the following spring when a dormant
nest was located in an attic.
In 1995 a total of 40 nests in Lerwick were reported to the Environmental
Services Department of the Shetland Islands Council. There was a
suggestion that there were fewer nests around the original site (although
this site itself was still in use) although possibly established nests
were not being reported again. Most nests reported in 1995 were further
west away from the shopping centre and in a suburban area with larger
gardens. There were also ten nests around Helendale on the western edge of
Lerwick. All nest sites were recorded in 1995, 13 were in roof or floor
spaces in buildings and the remainder were in holes in the ground. More
unusual sites were in a barrel and in a pile of peats (which are used as
fuel in Shetland). Elsewhere there were further reports of wasps in
Scalloway in 1995, and although again no certain nest site could be found
they were common around any gardens in the village with established trees.
photo right - SIC Environmental Services Department spraying wasps nest
It
would appear that all subsequent nests were founded by queens produced
from the original nest. The origins of the original queen is uncertain.
Common Wasps have colonised Orkney since 1986 where there are also
breeding records of Norwegian Wasp Dolichovespula norwegica. The
spread of certain Continental wasps into southern Britain has received
much attention in recent years (see for example Else 1994, British
Wildlife 5: 304-312). Perhaps we are seeing a similar spread of more
familiar species at the opposite end of Britain. It would be interesting
to know if there has been any expansion of range by any wasp in
Scandinavia. However, the location of the original nest near the shopping
centre of Lerwick, and the apparent move away from this area to more
suitable areas since then, lends support to the theory that the original
queen arrived in fresh produce.
What
of the future for this most northerly (and in the eyes of most Shetland
residents, unwelcome) wasp population? Two unusual sets of weather
conditions may help explain their successful colonisation. Recent winters
have been, by Shetland standards, relatively cold with fairly frequent
snow. Such conditions increase the likelihood of successful hibernation
for most insects as they reduce the damp, mild conditions which encourage
fungal infections in hibernating insects. In addition, the last few
summers have been relatively warm and sunny (again, judged by Shetland
standards), which can have only been beneficial to heat-loving
Hymenopterans such as wasps.
It
looks likely that the best efforts of the Environmental Services
Department will be in vain as most nests are only reported to them, and
hence treated, after the new batch of queens have departed. The increase
in the known population from one nest in 1993 to 18 in 1994 to 40 in 1995
reveals the ineffectiveness of treating nests late in the season.
Obviously the wasps carry out much of their life cycle without drawing
attention to themselves or causing any nuisance. A return to the sort of
weather Shetland experienced during the 1980s, with mild, wet and windy
winters, may prove to be a more effective control measure. These
conditions would make fungal infections of hibernating queens more likely.
However, it would appear that wasps have already established a strong
foothold in Shetlands’ two main centres of population.
Postcript: since this was written in 1996, wasps have consolidated
their position in Lerwick, where they continue to be pests, but are no
longer newsworthy, as they were in their early days. Further expansion was
noted in September/October 2004, when wasps appeared at Eswick, with up to
five in a day, and one was seen at Voe. Colonisation of further inhabited
areas seems likely to follow,
Nature in Shetland
