Rhantus suturalis (Macleay) (Coleoptera: Dytiscidae) and Hydraena nigrita Germar (Coleoptera: Hydraenidae) in Worcestershire
David M. Green
I recently recorded one specimen of Rhantus suturalis (MacLeay) (Coleoptera: Dytiscidae) in a moth trap (mercury vapour lamp) 10 October 2010 in the village of Little Comberton, British grid reference SO966431. As far as I know the only other record of the species in Worcestershire is Croome Park, Pond 9, Lickmoor outflow, British grid reference SO882456, 16 Sept 2005, by Garth N. Foster. Originally it was of JNCC Notable list B status, but is now found too widespread in Britain, despite its scarcity in Worcestershire, to qualify as Nationally Scarce (Foster 2010). The species is generally understood to feed on mosquito larvae, especially in ponds that dry up, & is found commonly in various parts of the world: this can be surmised by searching the Internet.
During October 2010 I found the species Hydraena nigrita Germar (Coleoptera: Hydraenidae) on two sites in the water of shaded ditches with a shallow flow of well oxygenated water with Gammarus pulex (Linnaeus) individuals present. Firstly on Bredon Hill in a ditch flowing through woodland not far from Elmley Castle (British grid reference SO971407) & secondly between the villages of Great Comberton & Little Comberton (grid reference SO961427) in a ditch running alongside a hedge in fields, where the shading is reduced this year owing to severe cutting of the hedge & trees along the hedge-line. However a fully grown hedge nearby provides some continuity of shade & it is near this hedge that the beetles were found. The site does not look significant in conservation terms. The species is now known too widespread to qualify for Notable status (Foster 2010). However, there are few records (three records are indicated for Worcestershire via the NBN website) in Worcestershire currently. It is a small species that would be often missed in non-specialised searching.
FOSTER, G.N. 2010. A review of the scarce and threatened Coleoptera of Great Britain Part (3): Water beetles of Great Britain. Species Status 1. Joint Nature Conservation Committee, Peterborough. Page 15, 16.