British insects: the families of Coleoptera


L. Watson and M. J. Dallwitz

Berosus Leach

Adults. Beetles sub-aquatic, or 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; when aquatic, replenishing air for respiration beneath the elytra indirectly from that acquired and held in a ventral plastron; when aquatic, collecting air at the water surface by exserting one antenna to achieve a continuum of air with the ventral plastron. Beetles 3.5–5.5 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 very short; not strongly asymmetric; 7 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. The pronotum not narrowing towards the rear. The mesoventrite not keeled, and without a dorsal point. 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. Mid-leg tarsi 5-segmented; pentamerous. Hind tarsi equipped with ‘swimming hairs’. Hind tarsi with the second segment longest; with the second and apical segments almost equal in length. Swimming hairs on both middle and hind legs; present on both tibiae and tarsi.

Elytra longitudinally striate (the striae punctured).

Adults not predacious. In silty ponds, drains, including brackish water.

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. Stemmata 6. 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 labium without ligula between the palps. The labial palps 4 segmented. The mesothoracic legs 5 segmented (including the pretarsus); with 1 movable claw. Visible abdominal segments 9. Tergum 9 of the abdomen entirely dorsal.

The larvae aquatic. The abdomen exhibiting functional abdominal spiracles, or without functional spiracles (?); having functional spiracles on anterior segments, or with functional spiracles confined to the the eighth segment. The larvae with long and narrow lateral gills on abdominal segments 1–7. The abdominal apex without a respiratory chamber (i.e., unusual in the Hydrophilinae). Abdominal tergum 8 without amature. The larvae predacious.

Worldwide and British representation. 4 species in Britain. Recorded from Scotland, Northern England, South-west England and Wales, South-eastern England, and Ireland.

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

General comments on this taxon. Maxillary palps longer than the antennae; the middle and hind legs with long pale swimming hairs on the tibiae, as well as on the tarsi; the elytra with 10 longitudinal rows of pits and grooves, with an additional short row on each shoulder between the first and second rows.

Miscellaneous. • Berosus signaticollis (Berosus Water-beetle: B. Ent. 240). • Berosus signaticollis: B. Ent. 240, legend+text. • Berosus signaticollis: B. Ent. 240, text cont.. • Berosus affinis, B. signaticollis, B. spinosus (from Joy, 1932).

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