Worcestershire Record No. 4 May 1998 p. 11

AN UNUSUAL WATER BUG FROM THE RIVER TEME: APHELOCHEIRUS AESTIVALIS (F).

On 28th March 1997 we had a family picnic by the River Teme at Ham Bridge between Martley and Clifton-on-Teme. This venue was chosen so that I could collect mayfly nymphs for the forthcoming mayfly identification course in April. The usual kick sampling in the shallows produced a good crop of mayfly nymphs as well as caseless caddis, water beetles, water shrimps etc. I decided to try in deeper water and very carefully kick sampled at a maximum water depth of approximately 0.75 m. This yielded further mayfly nymphs, small fish, and several specimens of a bug I knew only from illustrations, and a wader full of water!

I recognized the bug as Aphelocheirus aestivalis, the only UK representative of the family APHELOCHEIRIDAE. It is about 10 mm long and 8 mm wide and dark olive green with pale legs when alive. British specimens are micropterous (very short wings) although fully winged forms (macropterous) occur abroad. According to Southwood & Weston (1959) the distribution is based on the ancient river systems such as Trent, Severn, and Thames, and is widely distributed in Wales, the Midlands and the south. They quote Worcestershire as a locality where there are no records held by the Worcestershire Biological Records Centre. (Note: there was no Worcestershire BRC in 1959! Ed.)

The bug is found in medium-fast rivers with strong gravelly bottoms over silt and it seems to prefer hard water with little organic matter or vegetation. It is unusual in that it never surfaces and walks or swims rapidly along the river bed hunting for prey. It is a strict carnivore and its long rostrum can inflict a painful bite (take care when handling it - I didn't!). It breathes via a plastron system, the insect is covered with microscopic water repellent hairs at about 2,000,000 per square mm which trap a thin film of air next to the body. This film is self-renewing with oxygen diffusing in and carbon dioxide out. The bug can descent to a depth of at least 5 m and the abdomen bears pressure receptor organs to presumably regulate depth.

Despite diligent search I could not find this bug in water shallower than thigh-depth which, coupled with its habit of not surfacing, may mean that it is under-recorded. However we do not have many rivers like the Teme so it is probably restricted to suitable stretches of such rivers. I have kick sampled at similar depths in the River Severn above Bewdley but never found it.

The only bugs one might possibly mistake for Aphelocheiros are immature specimens of the saucer bug Ilyocoris cimicoides (L), but this species does not have the long rostrum, has a much wider head, much stouter front legs, and being a mainly pond and canal bug is never likely to occur in the same habitat (Savage 1989).

If you do search for Aphelocheiros take care! It is a deep water bug of fast rivers and ideally should not be searched for alone!

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