Worcestershire Record No. 3 November 1997 p. 7


By Brett Westwood

Britain's largest fly is alive and well and living on horse-pats in a Worcestershire meadow. That's what I'd like to be able to say anyway! The hornet robber fly Asilus crabroniformis is an impressive beast, especially when it zooms up from the grass nearby with an angry buzz. Only then do you realise why it gets its name. At close quarters it's no less dramatic, big and hairy with a black and yellow banded abdomen, and very observant eyes. I saw my first and only hornet robber in a sandy pasture at Hurcott near Kidderminster in August 1995. It was swelteringly hot, and I was taken aback when this huge wasp-like fly rose from the short pony-cropped turf. It flew a short distance and alighted on a pile of horse dung, real text-book behaviour. Following it around the field, dung-hopping, I wondered if it was born and bred on site. The habitat was just right. Hornet robbers like short grass on sand or limestone, grazed by cattle or horses. with lots of pats into which they can lay their eggs. Their larvae are predatory and eat beetle larvae also found in dung. What they don't like are Ivermectins, chemicals which kill off worms and parasites in cattle and other farm animals, because they also destroy all insect life, including robber fly larvae, in dung. As a result, the hornet robbers are becoming increasingly rare as the map shows. The destruction of old meadows and heathland has also taken its toll, so much so that Asilus is now a priority in the Biodiversity Species Action Plans, one of 116 plants and animals for which conservation in the UK is assured. English Nature and the Countryside Council for Wales are both committed to preserving its habitats, and along the way, the habitats of a great many other invertebrates too.

The hornet robber hasn't been seen since at Hurcott, but we haven't looked too hard! If you do see a huge (20-25 mms) yellow-banded robber-fly in the county, please pass on your information to Harry Green or the Biological Records Office at the Trust headquarters ..... we'd be very grateful to receive records.

Chinery, M (1986) Insects of Britain & Western Europe. Collins. Reprinted Domino Books 1993. [good pictures]
Chinery, M (1993) 3rd Ed. Insects of Britain & Northern Europe. Collins. [picture and a little more information]
Drake, CM (1991) Provisional Atlas for the larger Brachycera (Diptera) of Britain & Ireland. Biological Records Centre, NERC Institute of Terrestrial Ecology.
Oldroyd, H (1969) Diptera Brachycera section (a) Tabanoidea and Asiloidea. Handbooks for the Identification of British Insects Vol 9, part 4. Royal Entomological Society of London.

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