Early Hoverfly

The warm weather at the beginning of the week seemed to wake up a few insects and I have heard of several sightings of butterflies and bees. However, I had to go to a funeral in Suffolk on Tuesday so missed the best of the weather. Back at home on Wednesday I noticed a fly on the inside of the window. On taking a closer look I realised it was a hoverfly and it looked superficially like a Melanostoma. Anyway, I caught it and looked at it yesterday. It was a male and had rounded front tibia and tarsi and yellow, heavily dusted spots on the abdomen. I went through the Melanostoma key and it failed on abdomen shape and dusting on the frons. It also did not look right, with a fairly inflated frons and face. Going through the Platycheirus key it failed again. However, I remembered that Platycheirus ambiguus is an early species and has rounded front tibia and tarsi, so I tried that part of the key (ie abdomen with silver/bronze spots not yellow spots). It keyed out perfectly. I then checked in van Veen's key to the Northwest European hoverflies and again it keyed out. In this key it does say that the abdominal spots can be dusty yellow. One of the characteristic features of this species (and shared with only one other NW European hoverfly) is the curled bristly hair at the apex of the front femur and that was present on my specimen to confirm it. Platycheirus ambiguus is not well recorded, probably because of its early flight season. It is best searched for flying high around blackthorn when it is in flower. Peak records are from around the end of April, so this is still an exceptionally early record. I have found it locally around blackthorn and flowering fruit trees in late April so keep a look out for it.

That species has brought my garden total for hoverflies to 34. Must try harder!

With the change back to cold, damp weather and colder weather forecast, I suspect there will be no more hoverflies around for a while. However, the pussy willow buds are just starting to open in sheltered spots and they should provide nectar and pollen for the first few hoverflies of the season. An early hoverfly to look out for at sallow blossom is Cheilosia grossa. I have no records of this species, although it probably occurs locally. Its tendency to fly high and early in the season probably means it is overlooked. It is apparently more easily detected as a larva developing in the base of thistle stems later in the season. Stuart Ball has produced a guide to finding it and Cheilosia albipila. The guide can be downloaded from the Dipterists Forum website at:
http://www.dipteristsforum.org.uk/t104-Recording-Cheilosia-larvae-from-thistles.html