Dwarf web spider
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Dwarf web spider ( Theridiosoma gemmosum ) |
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| Theridiosoma gemmosum | ||||||||||||
| ( L. Koch , 1870) |
The Zwergradnetzspinne or dwarf spider ( Theridiosoma gemmosum ) is the only one in Europe occurring kind from the family of Zwergradnetzspinnen (Theridiosomatidae). It is holarctic , although the original distribution prior to human intervention is controversial.
description
It is a small orb web spider with medium-long legs, the body length of the females reaches about 2.1 to 2.5, that of the males 1.7 to 2 millimeters. As with all Theridiosomatidae, the abdomen (opisthosoma), which is somewhat elongated when viewed from above, is short and high arched, making its ventral side appear to be greatly shortened, the spinnerets sit close to the stalk (pedicellus), when viewed from above it overlaps widely with the carapace. This looks as if the abdomen were sitting in the middle of the prosoma when viewed from the side. The carapace of the prosoma is greenish-brownish in color, mostly with some radial dark stripes. As is typical of the family, the dark-colored sternum has two small dimples near the front edge. The light-colored abdomen has irregular dark spots in which small white, mother-of-pearl-like, shiny points (made from guanine ) are embedded; such points are also interspersed on the light sides of the abdomen. Alternatively, more extensive light spots result in a dark network drawing on a light background. The legs are brownish, the links of the legs are sometimes spotted or somewhat darkened towards the tip (distal). Of the two rows of four eyes at the front edge of the prosoma, the rear row is bent forward, the front and rear lateral eyes touch each other. The anterior median eyes are noticeably darker in color than the other pairs of eyes.
In the male, the very complex bulb of the pedipalps , which serves as a mating organ , is very large in relation to body size, it is almost spherical in shape. The embolus is partially covered in the (non-expanded state). The conductor is very large, pointed distally and has no apophyses. The epigyne of the female is heavily sclerotized, dark, a large scapus protrudes far outwards over two shallow pits, arched like a cap.
Habitat and way of life
The dwarf web spider can be found in wetlands such as reed beds , moors, alder swamps and other swamp forests or alluvial forests . It prefers shaded habitats. Mostly it lives in the immediate bank region of waters. It is considered a rare species almost everywhere in Europe, but can reach high densities of individuals in suitable habitats. It is considered common in North America.
The spider builds small, horizontally or vertically aligned webs of bicycles, over very wet swamp or over open water. Instead of a support spiral, two concentric rings are drawn in, the radial spokes are often branched out near the hub. Most individuals build nets in which the wheel net is pretensioned by a signal thread attached to the center of the hub as a tension thread, the spider keeps this taut, hidden in a hiding place, thereby deforming the net into a funnel. If a prey gets caught in the sticky catch spiral, it lets go, which entangles the prey even more strongly in the catch threads. The network is accelerated to 4 m / s within fractions of a second, which corresponds to 130 times the acceleration due to gravity.
Sexually mature males leave their nets and roam around in search of females, they no longer take in food. The mating takes place on a tension thread that the males release into the female network. Females eat the protein-rich thread, which has been interpreted as a form of the male "bride present". After mating, the female produces up to eight golden brown cocoons with a parchment-like cover. They reach three millimeters in diameter and are hung on a thread several centimeters long. Usually they are placed a little further away from the water than the safety nets. The young hatch in summer, they overwinter in the subadult stage. In parts of the range there are obviously two generations, with a maximum of adults in March and August / September. In more southerly parts of its distribution area, the reproduction probably takes place non-cyclically throughout the year.
Area
The species is distributed holarctic. There are finds from almost all of Europe, scattered eastward over Turkey to Central Asia (Iran). Find information is also available from East Asia, but there is speculation about a possible confusion with the very similar Theridiosoma epeiroides . In North America it was described a second time in 1953 under the name Theridiosoma argentatum Archer . She lives here in the eastern half of the continent, north to Newfoundland , south to Florida . The westernmost locations are in Minnesota and Iowa. Strangely enough, both Europe and North America believe that the species was introduced from the other continent.
Danger
According to the Red List of Endangered Animals in Germany, the species is considered "endangered" (Category 3).
Individual evidence
- ↑ a b Charles D. Dondale & James H. Speaker: The Orb-weaving spiders of Canada and Alaska: Araneae: Uloboridae, Tetragnathidae, Araneidae, Theridiosomatidae. Insects and arachnids of Canada 23. NRC Research Press, Ottawa, 2003. ISBN 978-0-660-18898-0 . Theridosoma gemmosum on page 329 ff.
- ↑ Michael J. Roberts: The Spiders of Great Britain and Ireland. Volume 1, Atypidae to Theridiosomatidae. Brill, Leiden 1985. ISBN 90-04-07658-1 . Theridiosoma gemmosum on page 222.
- ^ A b c Jonathan A. Coddington (1986): The Genera of the Spider Family Theridiosomatidae. Smithsonian Contributions to Zoology 422. 96 pages. Theridiosoma gemmosum on page 64 ff.
- ↑ Peter J. van Helsdingen (2005): Characteristic spider species of peat bog fenlands in the Netherlands (Araneae). Acta zoologica bulgarica, Suppl. 1 (European Arachnology 2005): 115-124.
- ↑ a b Heiko Bellmann: Kosmos-Atlas of the arachnids of Europe. Franckh-Kosmos Verlag, Stuttgart, 3rd edition, 2006. ISBN 978-3-440-10746-1 . Theridiosoma gemmosum on page 128.
- ↑ Lars Fischer: 130 times the acceleration of gravity: Spider turns its web into a super catapult. Spektrum.de , accessed on August 19, 2020 .
- ↑ J. Hajer, J. Hajer, D. Řeháková (2011): Mating behavior of Theridiosoma gemmosum (Araneae: Theridiosomatidae) - the unusual role of the male dragline silk. Archives of Biological Sciences (Belgrade) 63 (1): 199-208. doi: 10.2298 / ABS1101199H
- ↑ JR Pickavance & CD Dondale (2005): An Annotated Checklist of the Spiders of Newfoundland. Canadian Field-Naturalist 119: 254-275.
- ↑ R. Platen et al: Red List of Spiders, processing status 1996 (2nd version). In: Margret Binot et al. (Editor): Red List of Endangered Species of Germany. published by the Federal Agency for Nature Conservation, 1998. Series of publications for landscape management and nature conservation 55.
