Hydraenidae is a family of very small aquatic beetles with a worldwide distribution. These beetles are generally 1–3 mm in length (although some species reach 7 mm) with clubbed antennae. They do not swim well and are generally found crawling in marginal vegetation. Most are phytophagous but a few saprophagous and predatory species are known.
The family consists of more than 1300 species belonging to 44 genera. Genus Hydraena alone includes nearly 900 described species worldwide. Beetles are semi-aquatic, riparian and can walk on water surface. They feed on algae, bacteria, protozoans and detritus on wet stones and plant matter. The larvae, although preferring damp habitats near water, are non-aquatic and tend to drown easily. They have a distinct labrum and well developed galea of maxillae. 9th abdominal tergum has a pair of apical, re-curved ventral hook and 2-segmented urogomphi.