Worcestershire Record No. 6 April 1999 p. 26

HYDROCHUS ELONGATUS (SCHALLER) IN WARNDON

A Red Data Book Water Beetle - Hydrochus elongatus (Schaller)

The ponds in the Warndon villages have received much attention for their amphibian and botanical interest (Watson 1996). There have been a number of casual invertebrate surveys of a small number of these ponds over the last three years but only recently have any been fully surveyed. During spring and summer of 1998 a survey of ponds 27 and 28 was commissioned by Worcester City Council to clarify their invertebrate interest (Goddard 1998), with a view to subsequently controlling the three-spined stickleback population that is having a disastrous effect on the reproductive success of the great crested newt population in pond 28.

Both ponds held a good range of aquatic beetles, pond 28 had 20 species including one Red data Book species, Hydrochus elongatus (Schaller) Family Hydrophilidae, ('scavenger water beetles') . This dark grey-black beetle is fairly small and narrow, about 3.5 mm long with several longitudinal ridges running down each elytron. The beetle is listed as Red data Book category 3, nationally rare (Hyman, P.S. & Parsons, M.S., 1992), and as far as I can establish there are no previous Worcestershire records. It usually inhabits shallow clayey pools rich in vegetation. It is found in fens, open country and also deciduous woodland although it apparently avoids shaded sites. Pond 28 is somewhat shaded but Hydrochus was found in the shallows under submerged grasses in one of the more open places. There are many similar places in ponds in the Warndon pond cluster, one wonders if other ponds contain the beetle.

In addition to the above, pond 28 supported three other nationally scarce category B water beetles, Cymbiodyta marginella (F), Helochares lividus (Forster) and Cercyon convexiusculus Stephens. As with Hydrochus all are scavenger water beetles and are relatively small ranging 3 to 5mm in length. They are thought to feed on either fresh or decomposing plant material, although the genus Cercyon has many members that live in dung of various sorts, including waterlogged dung. Helochares - occurs in ponds, fens and ditches and apparently has a preference for recently restored ponds, it occurs in a number of other ponds in the Warndon area. Helochares and Cymbiodyta are relatively straightforward to identify using standard keys, however most species of Cercyon tend to be tricky and often require dissection to examine the male genitalia. Also the most up to date key is in German! although it has been translated and circulated to Coleopterists Newsletter subscribers. (I can supply copies at cost if anyone is keen).

It is surprising what can be found even within the city providing ones looks! Equipment for sampling ponds need not be elaborate, much good work can be done using a kitchen sieve as a net to sample the shallow edges of ponds where many beetles can be found. An opened out fertilizer bag or even a supermarket bag can serve as a sorting platform. Many common water beetles are easily identified and records for even the commonest species are thinly scattered. 

References: