Dryopidae
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| Billberg , 1820 |
The Dryopidae , in German (together with the closely related Elmidae ) often called hook beetles or claw beetles , are a family of beetles . The species live partly in water, partly in humid habitats and in riparian zones ("riparian") on land. The family includes almost 250 species, in Central Europe 13 species in two genera .
features
Dryopidae are between a good one and ten millimeters long, hard sclerotized and usually black or dark brown colored beetles. Rarely have the elytra shiny metallic to blue or green tones or red spots, usually the body appendages (legs are antennae , mouthparts ) brightened somewhat, often reddish brown or reddish. The body is often almost hairless or not noticeably hairy, but in some genera it can have thick and stiff hairs made up of short, upright hair. The abdominal side of the representatives living in the water has extremely dense and very short hair, invisible to the naked eye, which holds a film of air that is used for breathing under water ( plastron breathing ). The body outline is usually compact, more or less flattened oval, the head partially retracted into the pronotum, the mouthparts point downwards (hypognathic).
The structure of the antennae is typical of the family and the most important distinguishing feature to the Elmidae. These are usually very short and consist of a relatively small basic link, a very large second link, which is usually asymmetrically extended on one side, and a relatively short, one-sided sawn antennae lobe of nine to eleven links, the length of which hardly exceeds that of the second link. Variations of this basic form occur in some genera. The antenna of Ceradryops is only tripartite, that of Uenodryops is six-part. In Holcodryops , the first segment is expanded instead of the second. Usually the head has pits below the antennae in which they can be inserted.
The pronotum often has longitudinal furrows or longitudinal keels, sometimes the wing covers. The wing covers extend to the end of the abdomen, they are usually pulled out together somewhat pointedly towards the back. As a rule, dot stripes are formed on their upper side, sometimes in furrows. Most species have fully developed hind wings and are able to fly, a number of non-flightable species with shortened wings occur. The legs, which are usually strong, have five-limbed tarsi, the last limb of which is enlarged in a club-like shape and larger than the first four put together. A pair of pointed, long claws sit on it. The coxes (hips) of the hind legs can be placed under flat protrusions (thigh covers). The legs (femora) are usually hollowed out so that the splints can be inserted into this recess. The abdomen has five visible sternites on the abdominal side , the first four of which are close together and are connected to one another without a joint membrane.
The structure of the female genitals is characteristic. These are redesigned into a two-part, strongly elongated, often spear-shaped appendix, which probably serves as a laying stinger for laying eggs in bank mud or plant tissue. When extended, this can reach the length of the abdomen.
Larvae
The larvae of the Dryopidae are more or less elongated, cylindrical with a round body and relatively short legs. They are hard sclerotized and reddish, sometimes yellow to brown, colored, often with dark circles or dark markings. Their length is about 7 to 12 millimeters. The head is partially retracted into the trunk, the mouthparts point forward (prognath). There are usually six button-shaped larval eyes (stemmata) on the sides of the head, which can also be missing. The abdomen consists of nine segments, the rear of which are fused into a ring. A lid (operculum) with two hook-shaped appendages (limb rudiments) sits on the ninth segment on the abdomen. In contrast to the Elmidae, the larvae of the Dryopidae have no gills, they are air-breathing with open stigmas.
Dolls
Only a few species are known to have pupae of the Dryopidae. These are elongated, very hairy and whitish in color with a relatively soft cuticle. Most of the species have the rear end drawn out into a thorn or thread. Noteworthy are the dark and heavily sclerotized, clamp-like appendages on the back that are known as "gin traps", these are movable by muscles. They may be used for defense, but more likely for clinging to the doll's room.
Way of life
The Dryopidae live as adults either in the water or in humid habitats on land, usually in the bank zone of water. In all cases the larvae live on land (terrestrial). Both standing and flowing bodies of water are populated, including often very small ones with temporary water flow. In contrast to the Elmidae, the beetles tend to avoid currents and prefer quiet bays and the shore zone in flowing waters. Some genera, e.g. B. Helichus can also occur in fast-flowing areas. Many species of the shore zone live temporarily submerged in the water, sometimes on land and switch back and forth between these habitats throughout their lives.
The life cycle and biology of most species are poorly understood. At least some species need several years for larval development. As far as is known, both the beetles and their larvae feed on soft plant residues (detritus) and algae.
Systematics
The Dryopidae belong to a kinship group within the superfamily Byrrhoidea with a number of related families all living in water or in very humid habitats. The group was also regarded as a separate superfamily Dryopoidea. The phylogeny of this group is still unclear. The closest related and possible sister group could be the family Limnichidae according to the anatomy, especially the larvae .
literature
- Bernhard Klausnitzer (1984): Beetles in and around the water. The new Brehm library, Vol. 567. Ziemsen Verlag, Wittenberg.
- Jan Kodada & Manfred A. Jäch (2005): 18.3. Dryopidae Bilberg, 1820 (1817). In: Rolf G. Beutel & Richard A. Leschen (editor) Handbook of zoology. Volume IV. Arthropoda: Insecta. Part 38. Coleoptera. Volume 1: Morphology and systematics, Archostemata, Adephaga, Myxophaga, Polyphaga partim. Berlin, New York: Walter de Gruyter. pp. 496-508.
- AW Stefan: 42nd family Dryopidae. In H. Freude, KW Harde, GA Lohse (editor): Die Käfer Mitteleuropas, Volume 6.
