''Xysticus ulmi'', the swamp crab spider, is a European crab spider of the family

Thomisidae The Thomisidae are a family of spiders, including about 170 genera and over 2,100 species. The common name crab spider is often linked to species in this family, but is also applied loosely to many other families of spiders. Many members of thi ...

which prefers damp habitats. It was first described by the

German German(s) may refer to: * Germany (of or related to) **Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ger ...

zoologist Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the Animal, animal kingdom, including the anatomy, structure, embryology, evolution, Biological clas ...

Carl Wilhelm Hahn Carl Wilhelm Hahn (Lat. ''Carolus Guilielmus Hahn'', 16 December 1786 – 7 November 1835) was a German zoologist and author of the first German monograph on spiders. C. W. Hahn was an all-round natural scientist – not at all unusual for his t ...

in 1831.

Description

Males have a body length male of 3–4 mm, females 5-8.3 mm. The triangle on the

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

and the

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

are much more elongated in ''Xysticus ulmi'' compared to the other '' Xysticus'' spiders. The leaf-like pattern (the folium) on the dorsum is brownish with some whitish transverse lines towards the posterior. The legs are marked with fine spots. ''Xysticus ulmi'' is sexually dimorphic; males are darker than females and the

patella The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as m ...

and femora of the first and second legs are black.

Habitat

''Xyticus ulmi'' is usually found on low vegetation and in the ground layer in damp places, especially in

wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...

s and rough grassland, but in it can also occur in ditches alongside arable fields, hedges, roadside verges and woodland especially where the canopy is not closed, such as coppiced areas. In Europe it is found from the lowlands up to alpine regions.

Biology

Spiderlings are often found in the litter at the base of vegetation while adults usually occur in herbage. Females guard their egg-sacs, usually near the tip of higher plants. In Britain, the adult spiders are found mainly in May and June with females sometimes being seen into the autumn. Like other members of the genus it is an ambush predator, lying in wait for invertebrate prey. The males subdue the females by stroking their legs then tie them down with silk before mating.

Distribution

''Xysticus ulmi'' has a

palearctic The Palearctic or Palaearctic is the largest of the eight biogeographic realms of the Earth. It stretches across all of Eurasia north of the foothills of the Himalayas, and North Africa. The realm consists of several bioregions: the Euro-Sibe ...

distribution. It is found throughout Europe but it is absent from

Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...

. In Britain it avoids very dry areas and becomes scarcer in

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...

References

External links

* {{Taxonbar, from=Q140543 Thomisidae Spiders of Europe Spiders described in 1831 Taxa named by Carl Wilhelm Hahn