Hydraenidae

Definition

A family of minute aquatic beetles (order Coleoptera, superfamily Staphylinoidea) comprising roughly 1,300 species in 42 genera. Adults are 0.8–3.3 mm long, typically crawl on submerged surfaces or the underside of the water surface tension using air trapped beneath the body and elytra; some species possess gills permitting indefinite submersion. Larvae range from fully terrestrial to aquatic in early instars. Diet consists primarily of algae, spores, and plant detritus; adults of some species communicate via stridulation.

Etymology

From the type genus Hydraena (Greek hydra, water serpent + ena, possibly diminutive) + family suffix -idae

Example

Hydraenid beetles in the genus Ochthebius are common in thin water films on wet rock faces and mossy seeps, where they graze on algal biofilms.

Synonyms

• minute moss beetles

Related Terms

• Staphylinoidea
• Coleoptera
• Ochthebiinae
• Hydraeninae
• stridulation
• Elytra
• plastron respiration

Usage Notes

Sometimes called 'minute moss beetles' in English, though many species inhabit streams and seeps rather than moss per se. Distinguished from other small aquatic beetles (e.g., Elmidae, riffle beetles) by their habit of crawling on submerged surfaces rather than swimming, and by their plastron-based respiration. The family is divided into four subfamilies: Hydraeninae, Ochthebiinae, Orchymontiinae, and Prosthetopinae.