What Bug Is That? The guide to Australian insect families.

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Hydrophilidae

Overview

The largest Australian species belong to Hydrophilus . [Anderson 1976; Emden 1956; Watts 1987, 1988b.]

Description

Most adults may be distinguished by the short, 7- to 9-segmented antennae, with a 3-segmented, pubescent club, preceded by a glabrous, cup-like segment (cupule), the large clypeus and more or less angulate frontoclypeal suture, often attached to a median line (endocarina), and the well-developed maxillary palps, which are usually longer than the antennae. Larvae vary somewhat in form, but are typical for the superfamily, except for the presence of a maxillary mala in Spercheus . They differ from histerid larvae by having 6 stemmata on each side and usually possessing a metapneustic respiratory system, with only the 8th spiracles functional and these located in a respiratory chamber (atrium) at the end of the abdomen. Adult and larval hydrophilids have very different habits, although occupying the same habitats; the former are phytophagous or saprophagous, while the latter are predacious (except in a few exotic Helophorus ).

Spercheus platycephalus (Spercheinae) is a brown beetle with coarsely  punctate and costate elytra and a pubescent cupule; larvae differ from those of most hydrophilids in having an apical lobe (mala) on the maxilla and reduced spiracles. Spercheines inhabit stagnant ponds and adults and larvae are reported to walk on the underside of the surface film. Georissus (Georissinae) are minute, black and tuberculate, with a deflexed head concealed from above, a compact 1- or 3-segmented antennal club, large fore coxae fused to their trochanters, and 2 connate ventrites; larvae are typical for the family but lack a respiratory chamber and have 8 pairs of laterally placed spiracles. Hydrochus (Hydrochinae) resemble hydraenids in being elongate, narrow and somewhat metallic; they are found attached to plants in ponds or slow-moving creeks. The related Epimetopinae and Helophorinae do not occur in Australia.

The remaining groups of Hydrophilidae include the mainly terrestrial Sphaeridiinae and the aquatic Berosinae, Amphiopinae, Chaetarthriinae, Hydrobiinae and Hydrophilinae. The sphaeridiines are small to minute and may be abundant in decaying vegetable matter, dung, carrion and damp soil. The introduced Cercyon haemorrhoidalis and Sphaeridium discolor are common dung inhabitants; species of the endemic genus Notocercyon may be abundant in forest litter; and Pseudohydrobius species may be found in flowers (especially of Leptospermum ). Most aquatic hydrophilids are oval to globose, smooth and glabrous, often resembling Dytiscidae, from which they differ in having short, clubbed antennae and long maxillary palps. A ventral plastron, which communicates with the subelytral air reservoir, is also present; when the beetle rises to the surface, it breaks the surface film using its specialised antennal club, allowing communication between atmosphere and plastron. Larvae of Berosinae are unique in lacking functional spiracles (apneustic) and in having 7 pairs of lateral gills.

  • Enochrus sp.

  • Hydrochus sp.

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