Tony White has sent me the following article on cluster flies and ivy. I remember when I worked for what is now Tata Steel Europe in Corby that at this time of the year my office and other offices at the corners of the building were plagued by hundreds of cluster flies Pollenia rudis as these flies emerged from the surrounding grassland and sought overwintering quarters in the spaces above the false ceilings.
Ivy flowers and Pollenia species
Shelley reminds us that “The yellow bees in the ivy bloom” (Prometheus Unbound), but there are lots of diptera to interest us too, with ivy's nectar providing the last great feast of the year for many species.
Prominent among these are species of Pollenia and an excellent online key is to be found by looking for “Cluster Flies of North America”. Although it is a key to Canadian species it covers all British species with the exception of Pollenia amentaria and P. viatica (the latter species being easily recognised by its almost-black abdomen). Using this key I have been able to record Pollenia angustigena
and P. pediculata from ivy in the Byfield area (as well as the ubiquitous P. rudis) and it seems likely that these species are quite widespread and much under-recorded.
Now where can I find a reliable key to Calliphora species!
Some of last week's flies.
On Thursday morning I was at Grendon Lakes and noted large numbers of muscid flies sitting on tree trunks and foliage in full sunshine. They were very wary but I obtained three as a sample. They keyed out to be the common muscid Muscina levida, all males. I am not sure whether these were mating swarms or just a plentiful fly finding opportunities to warm up. Several Eristalis hoverflies were visiting ivy and on the few hogweed plants that were still in flower some other species were present. The most notable of these were Cheilosia soror but I also found a solitary Platycheirus that keyed out to P. splendidus. This species is primarily a Spring species and the specimen I took was a female, so it might be P. scutatus. This latter species is much more frequent in the Autumn and females of this group are only dubiously separable, so maybe it is better recorded under the aggregate name. At the same site, Jeff Blincow showed me an elongate bright metallic green soldierfly, which was the Autumn-flying Sargus bipunctatus.