Haliplids are insects of lowland ponds, littoral zones around lakes and slow moving water, some eg H.ruficollis and H.heydeni can be found in numbers among dense vegetation in small ponds, H.confinis and H.obliquus are dependent on stoneworks in hard water (Foster) and H.apicalis is a brackish water species. Many species can be found by careful examination of extracted samples of vegetation. Adults feed on algae but some are known to be at least partly carniverous eg H.lineatocollis feeds on Hydrozoa. They can remain submerged for long periods utilizing a plastron held under the coxal plates (Hurka), and fly on warm evenings, we have had them at MV in Cassiobury park. Eggs are laid on algae. Larvae are associated with algae but may be swept from marginal water, they do not swim but move slowly through the water or along the edge of the water along the bank. They are slender with terminal cerci (urogumphi) and in some species there are numerous long filamentous tracheal gills or short cuticular projections assumed to be gills. They feed by sucking out algal cells through a narrow canal in the mandibles. Pupation takes place in a chamber under the soil. Adults and third (last) instar larvae overwinter (Hurka, 1900).
For the purpose of recording, the Haliplidae are so distinctive that a family description seems unnecessary. These intensely interesting little beetles become instantly familiar, confining our discussion to 'true' water beetles because the various Polyphagan groups are so very different, the haliplids are unique in having rows, generally about ten, of well developed punctures on the elytra, Brychius has longitudinal raised ridges subparallel to the suture but again the puncturation is distinct. Regarding our other water beetles Gyrinidae are obviously different, Paelobiidae are larger, < 8mm, Noteridae have distinctive antennae (etc) and Dytiscidae lack the large dorsal puncturation. Distinctive though they are as a group, when it comes to specific determination some considerable familiarity with the various features will be necessary.
Antennae filiform and glabrous, apparently 10 segmented but actually 11. Peltodytes resembles Haliplus but here the terminal segment of the maxillary palps is longer than the penultimate, in Haliplus it is shorter. Head densely and often coarsely punctured, eyes entire, large and protruding. Temples well developed but usually hidden within prothorax. Pronotum shiny, broadest at base and strongly tapering to front margin, hind margin strongly sinuate and lateral margins finely bordered. Strongly punctate and in some species with a ridged furrow at base opposite fourth or fifth elytral stria which, except in H.lineatocollis (Mars.) where it extends halfway or more, reaches no more than a third of the pronotal length. Brychius is very different; pronotum broadest in front of middle and sinuate laterally. Scutellum not visible. Elytra broadest before middles or almost parallel sided, shiny with rows of strong punctures and generally with a few large punctures on the interstices, with longitudinal ridges in Brychius. Legs long and slender. Tarsi 5 segmented and tapering. Meso and meta tibiae and tarsi with long swimming hairs, the form of the tarsal segments is sometimes diagnostic. A feature unique to the Haliplidae is the greatly expanded posterior edges of the hind coxae, 'the coxal plates', these cover the basal abdominal sternites, hind trochanters and more than half the femora so that the hind legs can only be moved horizontally.
Males are distinguished by the dilated pro-tarsal segments which are furnished beneath with pale sucker hairs, obvious at X40.
Brychius is widely distributed and may be expected in running water and lakes.
Peltodytes is a mostly south eastern insect of fen drains and ponds.
At least 8 species of Haliplus are common in the south east (Friday)
Identification
Two modern works in English cover the British species:
Holmen, M. 1987 Fauna Ent. Scanda 20
Friday, L.E. 1988 Key to adults of British water beetles.
The group is dealt with in Vol 3 (1971) of Die Kafer Mitteleuropas by H.Freude but unless a wider fauna is being considered this is not a necessary work in view of the two excellent books above. Any work should be used in conjunction with the Andrew Duff's checklist.
Many species can be identified using external, including many underside, characters which are often subtle but nonetheless made clear in Friday's work. However most species of the 'ruficollis' group eg ruficollis (DG), sibiricus Mots., heydeni Wehncke, apicalis Thomson CG, fluviatilis Aube and furcatus Seidlitz rely on examination of the genitalia, females can usually only be identified by association. And because some are common it is often the case that numbers of these 'ruficollis' females are bought home but it is better not to try to assign these by comparison, stick to the males. With the males dissection requires patience and great care as the structures are delicate and variously transparent, they may be mounted on the card in a drop of DMHF or simply (and carefull) gummed. Look first at published figures so that the correct orientation can be acheived. Before any dissection begins try to key out the specimen so far as possible in case dissection damages any diagnostic parts. Genitalia can be slide mounted but pressure under the coverslip may cause slight distortion, which is enough to introduce doubts, so this must be born in mind.
With Haliplids you need to persevere, be diligent and very careful, spend time comparing dissections with line drawings; at first the differences seem so subtle as to make little sense but with each new mount a little more insight will be gained. Given a series of dissections things start to make sense and confidence will slowly be gained.
Haliplus
lineatocollis
Haliplus
ruficollis
Haliplus
ruficollis
Haliplus
ruficollis
Haliplus
ruficollis
Haliplus
ruficollis