Hydroscapha natans

The Hydroscaphidae are a family of beetles ( Coleoptera). Worldwide there are 13 species in three genera known to live in Europe, including two species.

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The beetles have a body length of one to two millimeters. Your body is spindle- shaped ( fusiform ) and tapers towards the end of the abdomen, which is not covered as in the swash beetles ( Gyrinidae ) of the wing covers. Your body is dark colored, smooth and covered with very fine hairs. The broad and short head is large in proportion to the rest of the body. The compound eyes are large and are not prominent, but are embedded in the lateral edge of the head. The antennae are about as long to reach the posterior edge of the sternum on the prothorax. They are five-membered in the genus Scaphydra, otherwise achtgliedrig. The last sensor segment is thickened club-shaped. The prothorax is short, the elytra are shortened and truncated rear. They only cover the first three or the first to fourth tergite of the abdomen. The tarsi are tripartite. The abdomen has six visible Ventrite the third to eighth segment. It tapers sharply towards the end of the abdomen. The second to fourth tergite is hairy characteristic fitting, the segments five to eight are very mobile. The tergites and sternites on the fifth to eighth abdominal segment are laterally fused, so that they form a sclerotized ring. The last, eighth sternite is back tapered.


The preimaginal stages of the genus Yara are unknown. The larvae of the other two genera have as well as the Imagines a spindle-shaped body which is wide at the front and rear tapers. The tergites are hairy laterally long. The head is broader than long, carries five simple eyes ( ocelli ) and has partial forward facing mouthparts. The sensors are bipartite and very short. The pronotum bears serrated scales. The legs have very strong, simple claws, which carry two flattened basal spurs. The tergites of the thorax as well as the first to seventh tergite on the abdomen wear at the posterior border rows of lanceolate hairs.


Pupation takes place as covered doll ( Pupa obtecta ), which remains in the exuvia of the last larva. Only the rear portion of the thorax and the abdomen based visible after the breaking of the larvae skin. These parts are more sclerotized than the non-visible. In the first to third abdominal segment functional trachea or tracheal gills are formed.

Occurrence and habitat

The genus Hydroscapha is widespread in western North America, Mexico, Eurasia, North Africa, Southeast Asia and Madagascar, the genus Scaphydra comes in southeastern Brazil and the genus Yara in Brazil and Panama before.

Both the larvae and the imagoes are common in rivers and streams found on algae, which are wetted with a thin film of water. You can very numerous occur in ideal habitats. The animals seem to prefer fast flowing and oxygen-rich waters, but can occur in different habitats. Occasionally, one can find the beetle on the sandy edge of waters, Yara Vanini is regularly detected in periodic streams and was first discovered in the moist mud. The species is, however, also detected in rocky areas and on cushions of moss and algae in rapids. The adults of Hydroscapha are occasionally found under stones in fast-flowing waters to a depth of one meter in the ground. The Hydroscaphidae inhabit waters with a wide range of temperatures. They are found both in hot springs, such as in Arizona, as well as in cold waters, such as the Amargosa River in Nevada.

Way of life

As far as hitherto known, larvae and adults feed on algae. Little is known about the development of the animals. The females of Hydroscapha place at the same time from just one large egg. Pupation takes place in that water, in which the last larval molt has occurred. The beetles are spreading also flying from what could be proven by finds in swimming pools.

Taxonomy and systematics

The family is characterized by the spindle-shaped body with broad head and thorax and significantly tapered abdomen both in the larvae as well as in the imago. The adults are distinguished from the other beetle families through their sclerotized ring, highly motile fifth to eighth abdominal segments and the characteristic flat coat on the third and fourth Hinterleibstergit. The two genera Scaphydra and Yara stand in a sister relationship, which is justified by the bifurcated apophysis with an elongated shaft which turns the steering wheel on the basal thickening of the aedeagus. Two species of the family are known from Europe:

  • Hydroscapha crotchi Sharp, 1874
  • Hydroscapha granule ( Motschulsky, 1855)