British insects: the families of Coleoptera


L. Watson and M. J. Dallwitz

Hydrophilus Müller

Giant Water Beetle.

Adults. Beetles aquatic; walking in water or free-swimming by conventional ambulatory motion of the legs, not diving strongly (?); moving in the water by alternate, walking leg movements; replenishing air for respiration beneath the elytra indirectly from that acquired and held in a ventral plastron; collecting air at the water surface by exserting one antenna to achieve a continuum of air with the ventral plastron. Beetles 38–48 mm long; body length/maximum body width 1.3–2.55. Beetles somewhat waisted.

Eyes two; not strongly protuberant; without bristles. Mandibles with a well developed mola; with well developed prosthecae. The maxillae with distinct galea and lacinia apically to the palp. The maxillary palps conspicuously elongated, sometimes longer than the antennae. The maxillary palps conspicuously elongated, sometimes longer than the antennae. The apical segment of the maxillary palps cylindrical to fusiform. The apical segment of the labial palps not expanded apically. Antennae red, very short; not strongly asymmetric; 9 segmented. Antennal scape not swollen. Antennae clubbed. Antennal clubs 3 segmented (the club hairy); preceded by a cupule. Antennal insertions visible from above, or hidden from above.

Prothorax without notopleural sutures. Mid-and hind-legs not as in Gyrinidae (q.v.). Hind coxae not extended laterally to meet the elytra; not shaped posteriorly to receive the femur. The hind coxae not produced behind into flat plates partly concealing the hind femora. Hind coxae without the steep transverse declivity characteristic of Dryopoidea. The inner parts (‘processes’) of the hind coxae not incorporated with the metasternum in a flat, median longitudinal keel. Tarsal segmentation formula 5, 5, 5. Some of the tarsi with a tiny basal segment that is hard to detect, or none of the tarsi with ‘hidden’ segments (?). The front tarsi with as many segments as the mid-tarsi; 5-segmented; apical segment longer than the rest together, or about as long as the rest together (triangular and much dilated in the male). Mid-leg tarsi 5-segmented; pentamerous. Hind tarsi flattened oar-like for swimming. Hind tarsi equipped with ‘swimming hairs’. Hind tarsi with the second segment longest; with the apical segment only about half as long as the second. Swimming hairs confined to the tarsi.

Adults not predacious. In dykes and marshes.

Larvae. The larvae elongate and more or less parallel-sided; vestiture restricted to fine hairs or setae; only very lightly pigmented or sclerotized; only very lightly pigmented. The antennae 3 segmented. Frontoclypeal suture between frons and clypeus indistinct or absent. The labrum and head capsule completely fused, with no suture apparent. Apices of the mandibles with a single lobe or tooth. The maxillary palps 4 segmented. The labial palps 4 segmented. The mesothoracic legs with 1 movable claw. Tergum 9 of the abdomen entirely dorsal.

The larvae aquatic. The abdominal apex with a respiratory chamber, formed from the 8th and 9th terga and enclosing a pair of enlarged spiracles. Abdominal tergum 8 without amature. The larvae predacious.

Worldwide and British representation. 1 species in Britain (H. piceus). Recorded from scarce, South-west England and Wales and South-eastern England.

Classification. Suborder Polyphaga; Infraorder Staphyliniformia; Superfamily Hydrophiloidea; Hydrophilidae; Subfamily Hydrophilinae.

General comments on this taxon. Described as a weak swimmer relative to Dytiscidae, but LW has never observed this species and has been unable to locate an adequate description of its method of swimming.

Miscellaneous. • Hydrophilus piceus (Great Water-beetle: B. Ent. 239). • Hydrophilus piceus (B. Ent. 239, legend+text). • Hydrophilus piceus (B. Ent. 239, text cont.).

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Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. British insects: water beetles. Version: 18th September 2012.’.