Friday, 30 August 2013

Late August 2013

Since my last blog about mimicry in hoverflies an example of its ability to confuse cropped up on BBC 2's recent Horizon science programme on what's happening to our bees. At one point it showed a "honey bee" which was, in fact, the hoverfly Eristalis tenax.  Oh dear! This is not the only example of hoverfly photos being used to represent bees. I remember browsing in a bookshop a few years ago and picked up a book entitled something like "Bees of the World" and the dust jacket photo was of an Eristalis hoverfly. It did not encourage me to regard the book as an authorative reference work.

Usually in late July and August Britain receives a large number of migratory hoverflies along with butterflies, moths and dragonflies. It is usually signalled by a sudden increase in the marmalade hoverfly Episyrphus balteatus and a few Scaeva pyrastri accompanying them. Although there have been plenty of Silver Y moths and Clouded Yellow butterflies about, I have not seen a great deal of evidence of a major hoverfly influx. There were plenty of E. balteatus about but I was seeing them in tens on most sites, not hundreds, and I have seen only one Scaeva pyrastri. There have been one or two sightings of Eupeodes latifasciatus, which may be a partial migrant, but overall I do not get the impression of a significant hoverfly migration in this area. I do not know if this is a general view across the country. I might raise the question on the Hoverfly Recording Scheme website.

One hoverfly that did catch my attention this week was of a Syrphus type with more black on the legs, particularly the hind femora, than with the usual species. Also the yellow bands on the tergites seemed to dip down towards the outer edges.  I managed to poot it off a bramble and took it home to identify. It turned out to be Didea intermedia, possibly a first for Northants. I took it in a wood with several blocks of conifer plantation. It was easy to key out and I was able to confirm it by comparing it with a couple of specimens I had from Speyside, its main stronghold in Britain. Interestingly, the following day someone reported one from Gloucestershire, a first for that county too. Also in the wood was Sphegina clunipes, a species for which we receive few records, although it is widespread in Britain. I rarely bother with conifer plantations but sometimes it is worth looking at different habitats, no matter how unpromising they may appear.