Article by Martin Evans and Roger Edmondson
During the BRERC South Gloucestershire Surveys in the summer of 2002 we had the chance to visit the 'Oldbury Power Pool'. This is a large artificial pool just to the south of Oldbury Power Station.
The site has been planted with a variety of native trees and shrubs and wetland herbaceous species have been planted around the edge of the pool. The surrounding grassland is semi-improved neutral grassland.
Although the surveys commissioned by South Gloucestershire Council are usually botanical, we also collect records of fauna as well as flora.
On our visit to this site at the beginning of July, the weather was very changeable, with bright sunny periods, bouts of heavy showers and a strong breeze. (John Kettley helped with this article!).
During the sunny periods we noticed that large numbers of insects were flying in a sheltered ride, just away from the pool. Umbellifers such as Hogweed, Hemlock, Hemlock Water-dropwort and Lesser Water-parsnip proliferate in this ride which has a wet ditch alongside the footpath. All of these plants are particularly attractive to flies and hoverflies.
Many hoverflies are very difficult to identify in the field. Fortunately, we were carrying a copy of Stubbs & Falks 'British Hoverflies' (1983, BENH) in the car, so we were able to identify the species where the features are distinctive.
We saw: Cheilosia illustrata, Chrysotoxum bicinctum, Episyrphus balteatus, Eristalis arbustorum, Eristalis nemorum, Eristalis pertinax, Eristalis tenax, Helophilus hybridus, Helophilus pendulus, Helophilus trivittatus, Myathropa florea, Parhelophilus versicolor and Volucella pellucens.
A trip to the site two weeks earlier had produced the following records:
Chrysotoxum bicinctum, Episyrphus balteatus, Eristalis tenax, Helophilus trivittatus, Leucozona lucorum, Rhingia campestris and Volucella bombylans.
A return trip dedicated to identifying these flies, with an experienced entomologist who would be willing to collect specimens to examine under the microscope, would definitely bring good results. Even a return trip to identify hoverflies in the field at a different time of the year would probably be interesting and productive.
The time spent at this site was partly due to the weather. We were forced to stay in the car during some of the worst downpours and used this time to identify the flies. Although none of the species are rare, a few such as Helophilus trivitatus and Parhelophilus versicolor are classed as Nationally Local and all of the records will help in the recording of Hoverfly distribution in this area.
So if you have a spare half hour on a bright day why not try some hoverfly recording. They do not have to be rare, or difficult to identify species to be important records. BRERC needs all of your records if we are going to be able to give a true picture of the distribution of species in the BRERC recording area.