Like some other animals on this website, I found this medium-sized beetle in my garden pond. Note the broadened parts of the forelimbs: these are adhesive discs, with which the male beetles cling to the female beetles during mating. There are two species of Hydaticus in the Netherlands and in the UK. Medium-sized beetles, with the typical characteristics of the Dytiscidae family. H. seminiger is fairly common, H. transversalis, less common, differs from this species by a yellow transverse band that runs across the elytra (van Nieukerken, 1992 and Foster & Friday, 2011), last mentioned authors describe H. transversalis as common in some regions of England.

Below, on the left, is another photo of the beetle, and below, right, two enlarged sections of that photo, showing details of the legs.

In the middle picture above, the large tibial spurs on the right hind-leg are conspicious. In the right picture, the round plate on the front leg appears segmented. The sucker discs/hairs are on the underside of this disc. There are also some of these discs on the darker part visible on the middle legs (out of focus).

Bibliography

See also the Bibliography of water beetles.

Nieukerken, E. van 1992, Dytiscidae - In M.B.P. Drost, H.P.J. Cuppen, E.J. van Nieukerken, A.M. Schreijer, (red.) 1992. De waterkevers van Nederland 154-156. - Uitgeverij K.N.N.V., Utrecht.