Crab spiders

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Crab spiders
Crab spider (Xysticus sp.)

Crab spider ( Xysticus sp.)

Systematics
Class : Arachnids (arachnida)
Order : Spiders (Araneae)
Subordination : Real spiders (Araneomorphae)
Partial order : Entelegynae
Superfamily : Thomisoidea
Family : Crab spiders
Scientific name
Thomisidae
Sundevall , 1833
Green crab spider ( Diaea dorsata ), female
Mutable crab spider ( Misumena vatia ) lies in wait for prey
Thomisus onustus , female
Mutable crab spider with captured honey bee on Phacelia sp. The bee carries the blue pollen of Phacelia on its legs.
Ozyptila praticola

The crab spiders (Thomisidae) belong to the most species-rich families of real spiders and comprise 175 genera with 2155 species worldwide . (As of December 2016)

The ambulance hunters are widespread worldwide from the temperate climatic zone to the tropics ; few species can also be found in subarctic or alpine habitats. The crab spiders, like all two-clawed spiders ( Dionycha ), are good climbers and therefore also at home in higher vegetation.

features

Crab spiders are easy to recognize by their very long front two pairs of legs. The first pair of legs of some males can be three to five times as long as the rear pair of legs. The front two pairs of legs are held at a slight angle in the resting position so that the animal looks like a crab with large claws. In addition, these limbs enable the crab spiders to walk sideways. Because of the noticeably different leg length from most other spider families, thick-jawed spiders (Tetragnathidae) and running spiders (Philodromidae) were often counted among the crab spiders, but this is an analogous feature and not an apomorphism . The colorful abdomen is particularly noticeable in some species.

Way of life

Crab spiders are pure ambush hunters who do not build fishing nets , and many local representatives do not even weave residential webs. The ability to make silk is used differently than other so-called " modern walking spiders ". The mutable crab spider, Misumena vatia , maintains provisions and bundles its prey into packets that are fastened below the inhabited flower. Many species use the spider silk as fall protection or, in the event of danger, let themselves fall securely on the thread and fall into a " stiff suspension ".

Mating and brood care

In Xysticus species, the silk also plays a role in mating. The female can be hung down by a thread or behaves rigidly, while she can be tied up by the much smaller male. The male "attaches" the female to the mat and then crawls under the opisthosoma to insert the bulbs into the genital opening. Tibellus species ( running spiders ) and Nephila species ( silk spiders ) show this behavior in a similar way ; however, the function is uncertain, because the female could theoretically free herself from the web.

Mating is preceded by courtship , and pheromones , "knocking signs" (see also wolf spiders ) and the sense of sight probably play a bigger role.

The female lays the well camouflaged eggs on a silk base and spins a lenticular cocoon made of several layers. The perennial animals mate only once, and the female guards the cocoon without eating. Nor can it be distracted by interference. Shortly before hatching, the mother bites open the cocoon, provides obstetrics, and then dies.

Capture of prey and camouflage

As with the related jumping spiders (Salticidae), the sense of sight of these two-clawed spiders is more important than that of web -building spiders.

Many crab spiders lurk on flowers and leaves for prey and, as masters of camouflage, can actively adapt their body color to the ground in a few days, so that one can usually read their habitat from the color of the female. The color variants range from bright white with red stripes to pale green or brownish ( changeable crab spider Misumena vatia ), bright yellow to emerald green (genus Heriaeus ), spotted, longitudinally striped ( Runcinia ), yellow to orange ( Synema ). Green or strikingly colored animals live on flowers and leaves, while darker species live on tree trunks or near the ground. Often the color-matched animals hunting for flowers are only perceived by many people when they look at a flower for a long time. Bizarre body shapes with humps and pits, points and vertical stripes support the colored camouflage of the animals by dissolving areas.

The crab spiders lurking on flowers also reflect UV light and are therefore particularly attractive to their prey. The UV reflection point is attractive for the prey. The pattern recognition of the spider's body is made even more difficult. The UV reflection, which is striking for insect eyes, acts as a camouflage for the spider and at the same time as an attraction. In experiments with the exclusion of UV light, prey continued to fly to flowers with crab spiders more frequently than flowers without crab spiders; So UV reflection is not the only strategy that crab spiders use to attract their prey.

The ability to reflect UV light in order to attract their prey and to make their own pattern recognition more difficult evolved several times in parallel with crab spiders. Crab spiders lurking on inanimate objects rather than flowers did not develop UV reflection.

Due to the attraction or accidentally, the prey animal comes in close proximity to the crab spider, so that it can seize pollinating insects with its two strong front pairs of legs. The crab spider avoids the sting of the larger prey and bites wasps and bees in the neck. The venom from their jaws is very potent. In contrast to the web-building spider species, crab spiders see and recognize their prey from a distance of 10 to 20 cm after it has already been perceived by low-frequency air and substrate sound.

Native genera and species

Other species outside Europe:

Systematics

The World Spider Catalog lists 175 genera and 2155 species for the crab spiders. (As of December 2016)

Web links

Commons : Crab Spiders (Thomisidae)  - Collection of images, videos and audio files

Thomisidae in the World Spider Catalog

literature

  • Heimer, Nentwig et al .: Spiders of Central Europe. An identification book. Parey, Berlin 1991, ISBN 3-489-53534-0 .
  • Jones: The Cosmos Spider's Guide. Franckh'sche Verlagshandlung, Stuttgart 1990, ISBN 3-440-06141-8 .
  • Sour, miraculous: the most beautiful spiders in Europe. Fauna-Verlag, Karlsfeld 1985, ISBN 3-923010-03-6 .
  • Foelix: biology of the spiders. Thieme, Stuttgart 1979, ISBN 3-13-575802-8 .
  • Wehner, Gehring: Zoology. Thieme, Stuttgart 1992, ISBN 3-13-772723-5 .

Individual evidence

  1. ↑ a b Natural History Museum of the Burgergemeinde Bern: World Spider Catalog Version 17.5 - Thomisidae . Retrieved December 23, 2016.
  2. ↑ Lars Chittka: Camouflage of predatory crab spiders on flowers and the color perception of bees (Aranida: Thomisidae / Hymenoptera: Apidae). In: Entomologia Generalis , 25, No. 3, 2001, pp. 181-187 ( PDF) .
  3. ↑ Astrid M. Heiling, Ken Cheng, Marie E. Herberstein: Exploitation of floral signals by crab spiders (Thomisus spectabilis, Thomisidae). In: Behavioral Ecology , 15, No. 2, 2004, pp. 321–326 ( PDF ).
  4. ↑ Astrid M. Heiling, Ken Cheng, Lars Chittka, Ann Goeth, Marie E. Herberstein: The role of UV in crab spider signals: effects on perception by prey and predators. In: Journal of Experimental Biology 208, No. 20, 2005, pp. 3925-3931, doi: 10.1242 / jeb.01861 ( PDF) .
  5. ^ Marie E. Herberstein, Felipe M. Gawryszewski: UV and camouflage in crab spiders (Thomisidae). In: Spider Ecophysiology. Springer Berlin Heidelberg, 2013. pp. 349–359, doi : 10.1007 / 978-3-642-33989-9_25 .
  6. ↑ Felipe M. Gawryszewski, Debra Birch, Darrell J. Kemp, Marie E. Herberstein: Dissecting the variation of a visual trait: the proximate basis of UV ‐ Visible reflectance in crab spiders (Thomisidae). In: Functional Ecology , 29, No. 1, 2015, pp. 44–54, doi: 10.1111 / 1365-2435.12300 ( PDF ).
  7. ↑ , Ellen AR Welti, Savannah Putnam, Anthony Joern: Crab spiders (Thomisidae) attract insect flower visitors without UV signaling. In: Ecological Entomology , 41, No. 5, 2016, pp. 611–617, doi: 10.1111 / een.12334 .
  8. ↑ FM Gawryszewski, Miguel A. Calero-Torralbo, Rosemary G. Gillespie, Miguel A. Rodriguez-Gironés, Marie E. Herberstein: Correlated evolution between coloration and ambush site in predators with visual price lures. In: Evolution , 2017, doi: 10.1111 / evo.13271 .