Elmidae

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Elmidae
Macronychus quadrituberculatus, from: GG Jacobson, "The Beetles of Russia and Western Europe" (St. Petersburg 1905–15), T. 42

Macronychus quadrituberculatus , from: GG Jacobson, “The Beetles of Russia and Western Europe” (St. Petersburg 1905–15), T. 42

Systematics
Class : Insects (Insecta)
Order : Beetle (Coleoptera)
Subordination : Polyphaga
Partial order : Elateriformia
Superfamily : Byrrhoidea
Family : Elmidae
Scientific name
Elmidae
Curtis , 1830
Elmis aenea
Limnius volckmari
Potamophilus acuminatus

The Elmidae , in German (together with the closely related Dryopidae ) often referred to as hook beetles or claw beetles , are a beetle family of Polyphaga that live in freshwater (aquatic) and are widespread worldwide . They include 1330 described species (as of 2008).

features

The beetles are small, between a little less than a millimeter and a good ten millimeters long, most species between two and three millimeters. Their body outline is usually oval, sometimes elongated with parallel body sides. The head is slightly retracted into the prothorax (usually up to the eyes) and protected from below by a semicircular protrusion of the prosternum , the mouthparts are directed downwards, never forward. The antennae are usually eleven-limbed (rarely reduced to seven limbs) and are simply thread-like or slightly culled towards the tip. This is the most important external distinguishing feature of the European species from the very similar family Dryopidae , in which mostly all antennae segments from the third onwards are drawn together to form a spindle-shaped, unilaterally toothed club (however, antennae clubs are also found in non-European genera in the Elmidae). The pronotum is arched upwards, keeled on the sides and in many genera and species has characteristic keels or grooves on the upper side, the presence and shape of which is very important in determining the species. The wing covers can also have such keels. In the resting position, the wing covers usually taper to the rear in a pointed oval shape and carry longitudinal rows of point pits. Most species have complete, membranous hind wings and are able to fly, but there are few species with shortened wings. The most important difference to the Dryopidae family is the shape of the female genitals. These are not drawn out into a laying stinger as in the Dryopidae, but usually shorter and softly sclerotized with paired protrusions (often called spinning pens, but probably sensory organs). The male genitals are in three parts with a central aedeagus and two lateral parameters; they are usually essential in determining the species.

The structure of the legs is characteristic of the Elmidae and Dryopidae families. These are always strong and designed as staple legs, the beetles have no swimming ability. On the five-limbed tarsi the last limb is noticeably enlarged, often longer than the four other limbs put together. At its tip are two enlarged, pointed claws. This gave the animals their German names, hook or claw beetles. The legs are greatly enlarged in some non-European genera, the leg length can exceed the body length in East Asian species of the genus Ancyronyx . This has given these beetles the popular name "spider beetles".

The Elmidae are mostly monochrome black. Some species show a metallic blue shimmer. In numerous species (not in Europe) there is a distinctive, yellow color markings made up of spots and bandages, which are interpreted as warning signs. Few species have a yellow-brown or reddish basic color.

Characteristic of the Elmidae and Dryopidae is their plastron breathing. For this purpose, the underside including the legs (Elminae) or the entire body surface (Larainae) are covered with an extraordinarily dense coating of very short, hook-shaped hairs and cannot be wetted by wax coatings. The hair can be so small that it can only be broken down with an electron microscope. Under water, the animals carry an air bubble under the wing covers with them. The area covered with hair is covered by a film of air that is in contact with the reservoir, making it look silvery white when viewed in the water. Carbon dioxide and oxygen can diffuse out of the air cover and thus renew the air supply (therefore the animals are dependent on oxygen-rich water). Since carbon dioxide is much more soluble in water than oxygen, its partial pressure in the air cover drops, which would normally make the bladder smaller and smaller and eventually use up the air supply. Due to the special design of the integument, the bladder can also remain in place under negative pressure (it is more or less supported by the bristles). Therefore, the beetles do not need, such as B. all swimming beetles (Dytiscidae) renew the air supply on the surface, but can stay submerged throughout their imaginal life. In some species of Larainae the plastron is less fully developed, these carry a larger air bubble with them under water and have to occasionally renew their air supply.

Larvae

The elongated larvae, up to 16 mm long, are, like the adults, well sclerotized. They are mostly parallel-sided and elongated, in some species (e.g. the genus Elmis ) the body is laterally leaf-shaped, so that a triangular body cross-section is formed. The flattened larvae mostly live on the surface of stones, those with a round body cross-section tend to be buried or in the gap system of the river bed. They have three pairs of legs, usually quite short, and like adults, they cannot swim. They breathe through gill tubes at the end of the abdomen, which are usually retractable and retractable and protected by a gill cover called an "operculum", which has a pair of claws and thus shows its origin as a pair of abdominal extremities.

Life cycle

All Elmidae lay their eggs in the water and live as larvae under water. The adults are also largely aquatic. In the Larainae there are some species that can be found permanently or temporarily outside the water as adults. However, these then always live in the immediate vicinity of the water, usually even in the area of ​​the water level.

The Elmidae lay their eggs, as far as known so far, individually or in small clutches cemented on the surface of stones or wood in the water. The larvae hatching after 5 to 15 days go through five to eight larval stages, depending on the species. The larvae usually sit on the surface of stones or other hard substrate and scrape off the organic growth ( periphyton ) from algae and other organisms on the surface. Some species specialize in particular substrates, e.g. B. Tufa (travertine), which precipitates from lime-saturated brook or spring water. As adults, these can be so encrusted with lime that they look like small stones. Few types, e.g. B. the North American Lara avara , feed on submerged deadwood in which they dig long superficial galleries. On this low-energy food substrate, they need four to six years to develop into an imago; the imaginal beetle then only lives about three weeks. Some other species were kept alive in the laboratory as adults but for up to ten years. Most elmid species, however, have a one-year development cycle ( univoltin or monovoltin). Sometimes northern populations of the same species take longer to develop.

All species pupate outside of the water. To do this, they dig a small cavity in the ground or under moss cushions near the shore, some species simply wait for the water level to fall in summer and pupate in the dry water bed. Others have expandable tracheal bladders with which they can rise to the surface of the water and float somewhere on the shore. The pupae have two long and stiff thread-like appendages on the pronotum and usually two pairs of hooks on the rear end. The hatching beetles normally do not run directly to the water, but instead perform a dispersion flight beforehand . You can recognize bodies of water by their reflective properties, as can be seen from individuals who have mistakenly landed on car paint or other surfaces with similar properties. Flying individuals of almost all species can be caught with window traps. If a suitable body of water is reached, the beetles submerge. At least in the subfamily Elminae, they never leave the water voluntarily and can usually no longer submerge themselves if they have dried out.

Way of life

Imaginal Elmidae, like the larvae, feed on algae and other detritus , rarely on living macrophytes . Most species live in flowing water, only a few prefer calmer waters. A few species live amphibiously in the area of ​​the shoreline, others in the swell area of ​​lakes. Even species of stagnant water are mostly dependent on water movements and do not occur in deeper water layers, the maximum water depth reached is around ten meters in a few lakes. Most species are flow specialists and prefer fast flowing waters.

Within the family there are some species with special adaptations. There are specialized types such as B. in thermal springs. Very few species specialize in underground waters ( stygobiont ) throughout the Palaearctic been such. B. only one species found in Morocco. In flowing waters they occur from the source brook to large rivers, with the average number of species increasing with the size of the water. The number of species also increases towards the south, both in Europe and worldwide. Within the tropics, rivers of all kinds are populated with many species. Although most species prefer hard substrates such as stones, there are also species that specialize in sand and other fine substrates.

Elmidae and their larvae become prey for fish. However, their share in the intestinal contents is usually lower than their individual share in macrozoobenthos , so that their importance as fish food animals is rather low. While some North American species with yellow warning markings were spurned by predators in food choice experiments, the European species are z. B. eaten by trout without hesitation.

Elmidae are considered pointer organisms for good water quality, many are flagship species with a low saprobic index within the saprobic system , i. H. Pointer for organically unpolluted water. Some species can survive in moderately polluted waters if the current is fast enough. A number of species are habitat specialists, e.g. B. on spring tuff or dead wood, these species are used as indicator species in the context of river typing, some species are indicator species for good or very good water quality within the framework of the European PERLODES assessment procedure.

Systematics

In the past, the Elmidae were often listed as a subfamily of the Dryopidae, which are closely related to them, and the German names "Klauenkäfer" or "Hakenkäfer" are used for both families, which are morphologically very similar. Scientific synonyms for the family name Elmidae include: a. Helmidae, Elminthidae and Limniidae. The family name is derived from the genus Elmis Latreille, 1802. The meaning and origin of this name are unknown. The family's monophyly has not been tested up to date; its relationship to the Dryopidae and a number of other families (Heteroceridae, Helocharididae) has not been conclusively clarified.

The Elmidae are mostly classified in the superfamily Byrrhoidae, occasionally with the aquatic families of this superfamily, which are probably more closely related to one another, also in a separate superfamily Dryopoidea, which would then be sister taxon of the Byrrhoidea. They are divided into two subfamilies, the Larainae (synonyms: Larinae, Potamophilinae) and the Elminae.

The following list contains the 54 European species of Elmidae according to "Fauna Europaea" (2007):

Subfamily Elminae

Subfamily Larainae

Individual evidence

  1. ↑ MA Jäch, M. Balke: Global diversity of water beetles (Coleoptera) in freshwater. In: Hydrobiologia Volume 595, 2008, pp. 419-442. doi : 10.1007 / 978-1-4020-8259-7_43 .
  2. ↑ Hendrik Freitag, Manfred A. Jäch: The genus Ancyronyx Erichson, 1847 (Coleoptera, Elmidae) in Palawan and Busuanga, (Philippines) with descriptions of six new species. In: Zootaxa Volume 1590, 2007, pp. 37-59.
  3. ^ RJ Steedman, NH Anderson: Life history and ecological role of the xylophagous aquatic beetle, Lara avara LeConte (Dryopoidea: Elmidae). In: Freshwater Biology Vol. 15, 1985, pp. 535-546.
  4. ↑ HP Brown: Survival records for elmid beetles with notes on laboratory rearing of various dryopoids (Coleoptera). In: Entomological News Volume 84, 1973, pp. 278-284.
  5. ↑ Carles Hernando, Pedro Aguilera, Ignacio Ribera: Limnius stygius sp.nov., The first stygobiontic riffle beetle from the Palearctic Region (Coleoptera: Elmidae). In: Entomological Problems , Volume 32, No. 1, 2001, pp. 1-4.
  6. ↑ Ignacio Ribera, Garth N. Foster, Alfried P. Vogler: Does habitat use explain large scale species richness patterns of aquatic beetles in Europe? In: Ecography Volume 26, 2003, pp. 145-152.
  7. ↑ cf. at Fliessgewässerbevalung.de
  8. ↑ MA Jäch: Elmidae Curtis, 1830 and Elmis Latreille, 1802 (Insecta: Coleoptera): Proposed conservation as correct spelling and of feminine gender respectively. In: Bulletin of Zoological Nomenclature Volume 51, 1994, pp. 25-27.
  9. ↑ cf. Cladogram in Toby Hunt, Johannes Bergsten, Zuzana Levkanicova, Anna Papadopoulou, Oliver St. John, Ruth Wild, Peter M. Hammond, Dirk Ahrens, Michael Balke, Michael S. Caterino, Jesús Gómez-Zurita, Ignacio Ribera, Timothy G. Barraclough , Milada Bocakova, Ladislav Bocak, Alfried P. Vogler: A comprehensive phylogeny of beetles reveals the evolutionary origins of a superradiation. In: Science Volume 318, 2007, pp. 1913-1916. doi : 10.1126 / science.1146954
  10. ↑ January Kodada, Manfred A. Jäch: Elmidae . Chapter 18.2. In: RG Beutel, RAB Leschen (Ed.): Coleoptera, Beetles. Volume 1: Morphology and Systematics (Archostemata, Adephaga, Myxophaga, Polyphaga partim). Handbook of Zoology, Volume IV Arthropoda: Insecta Teilband 38. Walter de Gruyter, Berlin-New York 2005, pp. 471-496.
  11. ↑ Fauna Europaea Version 2.5, accessed on August 10, 2012

literature

  • Jan Kodada & Manfred A. Jäch : 18.2 Elmidae. In: Rolf G. Beutel & Richard Leschen (editor): Handbuch der Zoologie / Handbook of Zoology. Volume 1: Morphology and Systematics (Archostemata, Adephaga, Myxophaga, Polyphaga partim). De Gruyter, 2005.
  • HB Leech & HP Chandler: Aquatic Coleoptera. In: Robert L. Usinger (Ed.): Aquatic Insects of California, with Keys to North American Genera and California Species. University of California Press, 1968.
  • J. Malcolm Elliott: The ecology of riffle beetles (Coleoptera: Elmidae). Freshwater Reviews 2008/1, pp. 189-203, 2008.
  • HP Brown: Biology of riffle beetles. Annual review of entomology, 32, pp. 253-273, 1987
  • H. Brown (1991): Elmidae (Dryopoidea). In: F. Stehr (Ed.): Immature Insects, Vol. 2. pp. 404-407. Dubuque, Kendall & Hunt Publishing Company, Iowa, USA, 1991
  • G. Hammond (2009): Elmidae , Animal Diversity Web, accessed July 14, 2009.

Web links

Commons : Elmidae  - Collection of images, videos and audio files