Caucasian Spiders

In the Caucasus we find a highly diverse spectrum of habitats in all major ecosystems of the region (cf. WWF Ecoregion Conservation Plan for the Caucasus, PDF). Most spider species live in Forest ecosystems because these cover most of the area of the Caucasus and are structurally and climatically the most complex ecosystems to be found. The next most important ecosystems for Caucasian spiders are the High Mountains because large parts of the region are situated above the timber line, namely in the Great Caucaus north of Georgia and Azerbaijan and the Lesser Caucasus to the south of both countries. As the eastern part of the Transcaucasian depression is characterized by dry or very dry (arid) conditions, ecosystems of dry mountain shrublands and steppe harbour many characteristic spider species in eastern Georgia and Azerbaijan. Some spider species live in close affinity to freshwater ecosystems or - in the case of one species - even within the water itself.

1. Spiders in Forest Ecosystems

Spiders are very abundant in forests everywhere on earth - not only in the Caucasus. They dwell in large numbers in all forest layers: the ground layer, field layer, shrub layer, and even canopies of all trees in the forest. Within these layers certain spiders species prefer one or more microhabitats in which to hunt for prey, rest, molt, mate and construct their cocoons. In the Caucasus forest ecosystems naturally extend from the seashores of the Black Sea and the Caspian Sea to the timber line, which in the Caucasus extends to well above 2000 m a. s. l.

Spider species living in the ground layer (0 - 15 cm above the ground) of forests prefer microhabitats such as soil (burying or between roots) or leaf litter, the underside of rocks and pepples, in or at dead wood on the ground, in moss cushions, etc. In the Caucasus species like the bird spiders of the family Nemesiidae (e. g. Raveniola pontica (Spassky, 1937)) live in burrows in the soil just as all species of the wolf spiders (Lycosidae, e. g. tarentulas like Lycosa praegrandis C. L. Koch, 1836) and many species from other families.

The field layer (ca. 0.15 - 1.8 m) is inhabited by spiders constructing webs or running freely on herbs and grasses. Among them many beautiful orb web-weaving species like Neoscona adianta (Walckenaer, 1802)) can be found. The infamous and toxic black widow spiders construct their irregular webs between grasses and herbs but their cocoons are often hidden under rocks (cf. Latrodectus tredecimguttatus (Rossi, 1790)).

Spiders inhabit bushes and small trees of the shrub layer (1.5 - 4.5 m, = lower canopy). Again, many web spiders can be found on bushes (e. g. Araniella cucurbitina (Clerck, 1757)) but also freely running spiders like Anyphaena accentuata (Walckenaer, 1802).

Tree canopies (4.5+ m) are the least studied layer of the forest ecosystems. Some species prefer the cracks and crevices of the trees’ bark (e. g. Coriarachne depressa (C. L. Koch, 1837)) but other species extend their activities to the very end of the twigs high up in the canopies (e. g. Philodromus aureolus (Clerck, 1757).

Within forests a number of spider species are adapted to the life in cave habitats. Most of the Caucasian cave spiders can be found in Caucasian caves only or are distributed in regions close to the Caucasus. Among them are species like Troglohyphantes birsteini Charitonov, 1947, Meta bourneti Simon, 1922 or Carpathonesticus caucasicus (Charitonov, 1947).

A large percentage of the Caucasian Forest Ecosystems has been transfered to some extend from natural forests to cultural landscapes characterized by settlements, agriculture and industrial complexes. Nevertheless, many spider species are abundant in such anthropogenically altered habitats and can be found even within houses (e. g. Pholcus phalangioides (Fuesslin, 1775), Scytodes thoracica (Latreille, 1802) or Tegenaria domestica (Clerck, 1757)).

2. Spiders in High Mountain Ecosystems

High Mountain Ecosystems start above the tree line (in the Caucasus between 1700 and 2700 a. s. l.) where no trees can exist due to the harsh conditions and short vegetation period at such high altitudes. Based on vegetational characteristics a number of altitudinal zones can be distinguished: the alpine zone, the subnival zone and the nival zone. As in most other animal and plant groups the species richness of abundance spiders decreases with altitude. However, a number of high mountain specialist species live only here. They are characterized by adaptations to the comparatively simple structured habitats, the harsh environmental conditions and short vegetational period at high altitudes.

Spiders can be found in all high mountain zones. Directly above the tree-line in the alpine zone (1700 - 4000 m), spiders mostly live on the ground between rocks and plant roots or on the few woody plants left (e. g. on Rhododenron caucasicum, R. luteum). At above 4000 m last grassy patches begin to disappear with increasing altitude and become more and more patchy (sub-nival zone) Above the climatic frontier of permanent snow (true nival zone) the last few remaining spiders live in a few sheltered microhabitats such as rock crevices, temporary snow and ice caves or between the remaining mosses and lichens. A number of yet undiscovered spider species are expected in such remote habitats and collecting spiders there would most probably yield very interesting results.

The air in the high mountains is usually dry, too. As most spider species are vulnerable to dehydration, they try to find more mumid microhabitats for web-making, hunting, reproduction, etc. Therefore, crevises and the lower surface of rocks in old rockslides are populated by a community of spiders. They are mostly characterised by small species (e. g. Linyphiidae, Theridiidae) but occasionally larger spiders of the family Gnaphosidae can be found, too. Older rockslides with a beginning succession of mosses and higher plants shelter more spiders because of the more diverse habitat-structures and a moister microclimate compared to more recent, dryer rockslides into which spiders still need to immigrate.

3. Spiders in Dry Mountain Shrubland Ecosystems

The arid mountains of the Southern and Eastern Caucasus are dominated by a shrub vegetation dominated by thorny shrubs like Christ’s Thorn (Paliurus spina-christi), Pallas’ Buckthorn (Rhamnus pallasii) and other species. A number of xerophilic (warmth-loving) spider species known from the Eastern Mediterraneis can be found, e. g. Agelena orientalis C. L. Koch, 1837, Argiope lobata (Pallas, 1772) or the Black Widow Latrodectus tredecimguttatus (Rossi, 1790).

4. Spiders in Steppe Ecosystems

Steppe habitats are destributed in Eastern Caucasus. No trees live here but grass is very abundant (Stipa sp., Koeleria sp.). The same heat- and drought tolerant spider species as in the dry mountain shrublands can be found in steppes, too.

5. Spiders in Freshwater Ecosystems

Of all the 40,000 known spider species only the ‘water spider’ Argyroneta aquatica (Clerck, 1757) is well adapted to a life submersed in freshwater habitats like lakes, ponds and slow flowing rivers. There it constructs a web between water plants into which it suspends air bubbles for breathing, feeding and molting.

A number of spider species are, however, associated with freshwater habitats without actually living within the water itself. They dwell on the vegetation near the lakes and rivers where the find suitable moist conditions for their activities.