Sphaerius

Sphaerius is a genus of beetles, comprising 23 species, which are the only members of the family Sphaeriusidae. They are typically found along the edges of streams and rivers, where they feed on algae; they occur on all continents except Antarctica. Three species occur in the United States.

The overall form of the beetle is convex, glossy, dark brown or black with some markings possible. The head is prominent, with relatively large eyes set far apart, and capitate antennae. Total length ranges from 0.5–1.2 mm.

The beetles occur in a variety of damp environments, including mud, under stones, among plant roots and leaf litter, and in mosses in bogs. They store some air underneath their elytra.

Females produce a single large egg at a time.

The family used to be known as "Sphaeriidae", but the name was preoccupied by a family of freshwater clams. The name was inappropriately replaced with "Microsporidae" (by changing the genus name to Microsporus), but this act has been superseded by a return to the use of Sphaerius and a reformation of the family name as Sphaeriusidae. The position of the family within Coleoptera has also changed a number of times.