Hydrochus

Distinguished from other Hydrophiloidea by the seven-segmented antennae with a three-segmented club (versus reduced segmentation in some relatives), the pronotum narrower than the elytral base, and the characteristic tarsal formula (usually 5-5-5 or 4-4-4). The cup-like basal segment of the antennal club is particularly diagnostic. Species-level identification typically requires examination of male genitalia.

Slow-moving streams and stagnant water bodies with dense vegetation. Adults are associated with submerged surfaces and vegetation. Larvae are strictly benthic, inhabiting the bottom of water bodies, often burrowing into crevices and hollow dead grass.

Worldwide distribution. Documented from North America (including Eocene fossil Hydrochus relictus from the Green River Formation), Central America (Belize, Costa Rica, Honduras, Mexico, Nicaragua, Panama), South America (Bolivia, Brazil, Colombia, Paraguay), Europe, North Africa (Morocco), and Asia (Iran, Japan).

Adults are thought to consume algae and plant detritus. Larvae feed on annelid worms; specifically, H. japonicus larvae have been observed feeding on Naididae worms.

Eggs laid in silk cases attached to substrates, usually plants. Larvae live benthically at the bottom of water bodies, burrowing into crevices such as hollow dead grass. Pupation occurs within such crevices. Larvae possess terminal spiracular atria and breathe underwater without surfacing.

Adults are sluggish crawlers along submerged surfaces. Air is stored in a bubble on the underside of the body; antennae are used to transfer atmospheric air to this bubble. Larvae remain at the bottom of water bodies and do not surface to breathe.

Benthic detritivores and predators; larvae consume annelid worms, while adults process algae and plant detritus.

• HydrophilidaeFormerly treated as a subfamily of Hydrophilidae; Hydrochidae is now recognized as a distinct family. Hydrochus differs in antennal structure (seven-segmented with three-segmented club versus typically clubbed but differently segmented antennae in Hydrophilidae) and pronotum shape.
• HelophorusMolecular phylogenetic studies suggest Hydrochus may be sister to Helophorus, but Helophorus species have different antennal and body proportions, and are typically associated with different microhabitats.
• GeorissusSuggested as a related genus based on molecular phylogenetics; Georissus species are typically smaller, more compact, and associated with different substrates.

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Taxonomy of Central American water beetles in the genus Hydrochus Leach, 1817 (Coleoptera: Hydrochidae)
• The Hydrochidae (Coleoptera) of Morocco with a redescription of Hydrochus cf. obtusicollis Fairmaire, 1877
• Taxonomy of water beetles in the genus Hydrochus Leach, 1817, from Bolivia, Brazil and Paraguay (Coleoptera: Hydrochidae)
• Hydrochus farsicus sp.n. from Iran and notes on other Palearctic species of the genus (Coleoptera: Hydrophiloidea: Hydrochidae)
• Laboratory rearing of Hydrochus japonicus (Coleoptera: Hydrochidae) suggests larvae live at the water bottom
• Aquatic Hydrophilidae and Hydraenidae of Wisconsin (Coleoptera). I. Introduction, Key to Genera of Adults, and Distribution, Habitat, Life Cycle, and Identification of Species of <i>Helophorus</i> Fabricius, <i>Hydrochus</i> Leach, and <i>Berosus</i> Leach (Hydrophilidae), and Hydraenidae