Spring? Not really

Prior to the latest batch of snow there was one day when it actually felt a bit like spring. After a long winter of staring down the microscope at specimens from previous years, I was desperate for some fieldwork so I stopped in at Stedham Common for a couple of hours. The sun was shining but there was still a cold wind. I had hoped the odd early sallow might have been in flower but the only flowers to be found on the site were gorse - a species which I always find to be poor for nectaring insects apart from honey bees.

However there were a few birch trees that had been felled during the winter which were oozing sap from the stumps and this was attracting a few flies. Surprisingly, despite the cool temperature they were quite agile and difficult to catch. The most common species were Scathophagids, mainly the 'Yellow Dung Fly' Scathophaga stercoraria but a few more interesting species were seen.

Sepsids are small, shiny, ant-like flies. They have varying amounts of dusting on the sides of the thorax which are important identification features and the males have interesting armature on the front femurs. Species in the genus Sepsis all have a small blackish dot near the apex of the wing.

Sepsis species

Male Sepsis sp. showing spines and tubercles on the front femur and silvery dusting on the side of the thorax

Surprisingly, the three specimens that I took were all different species. Sepsids generally breed in nutrient enriched places and they can often be seen around dung or enriched mud. They wave their wings around in a characteristic way.

Also around the stumps were a number of cluster flies or blowflies (Calliphoridae). Species in the genus Pollenia were most frequent. These can easily be recognised as belonging to the genus as they have crinkly golden hairs beneath the black bristles on the thorax (although these do wear off and can become confined to the sides of the thorax only).

Pollenia sp. The golden hairs have mainly worn off the top of the thorax but can still be seen on the sides

Paul Brock's photographic insect guide is highly misleading in respect of this genus. He illustrates Pollenia rudis and states that it is easily identifiable on account of the chequered abdomen and golden hairs. In fact there are 8 species of Pollenia in Britain, most of which are fairly common. All have the golden hairs and all bar one have a chequered abdomen. These can only be separated by examining microscopic features. The larvae of Pollenia species are predators of earthworms.

Aside from the Scathophagids, Sepsids and Calliphorids, I saw a few Drosophilids (fruit flies) which will have to await identification when I have more time, and a Mycetophilid (fungus gnat) which evaded capture.

There was little else around. A couple of the birch-feeding Lygaeid bug Kleidocerys resedae were active and two Yellow Horned Achlya flavicornis moths were found at rest on an old birch stump.

Slim pickings and the subsequent weather has resulted in a return to the microscope.