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Ecology

Spider ecology has become more important in recent years, as the complex roles of spiders in ecosystems become apparent (See Wise 1993, Foelix 1996, and others). Many researchers in past ecological studies have simply lumped spiders all together, while separating the various insect predators. While spiders are generalist predators, this does not mean that they are general in their prey capture. They tend to take certain arthropods more commonly than others. In some, such as the bolas spiders (Mastophora spp.), prey capture is so restricted that only a few species of moths are eaten, and of these only males brought to the dangling bolas of venom-treated gum by a pheromone analog (Eberhard 1977). Most spiders are not this restricted, but it may be noted that orb-weavers catch few non-flying insects, flower-dwelling crab spiders few non-pollinator insects, and wolf spiders few actively flying insects. Spiders thus tend to act as if they were in guilds of prey-capture specialists (Culin & Yeargan 1983a, b, c, Young & Edwards 1990, Richman, et al. 1990) as well as being in an overall generalist predator guild as defined by Wise (1993). The multi-guild character of spider faunas has only been appreciated in relatively recent times and needs to be examined more thoroughly.

The local distribution of spiders is largely based on the availability of food and sites for webs, burrows, or just cover. It has been shown that spider numbers generally increase when they are provided with mulch in garden beds (Riechert & Bishop 1990) and deep leaf litter or pine needles often have a large fauna of ground-dwelling spiders. Tree, shrub and herbaceous plant dwelling spiders of course need their particular substrate. Ballooning (see section on behavior) is a major means of dispersal by spiders. By this method spiders were among the first living things to appear on the new island produced by the eruption of the volcano Krakatoa in 1883 (Bristowe 1931). Similarly, Mt. St. Helens was repopulated by 40 species of spiders in only two years after the major eruption of 1980 (Edwards 1986). From a geological perspective, spider species and even whole spider family (especially mygalomorphs) distributions have been affected or determined by continental drift (vicarience). In much more recent times many spider species have been transported by human activity to far-flung areas of the globe. Australian red-backed spiders have been imported to Japan, Central American tarantulas to Florida, the European hobo spider to the Pacific Northwest and the European sowbug-eating spider to the United States. New species are arriving every year as our ability to move around the planet becomes more enhanced In some areas of the United States all of the pholcid and scytodid spiders are imports. Unfortunately the hobby of rearing exotic arachnids sometimes results in the accidental or deliberate release of exotic spiders, such as some of the red-legged tarantulas found in citrus groves in Florida (G. B. Edwards, personal communication). However it turns out, the introduction of exotic spiders will continue, although the danger from venomous exotic spiders is certainly over-rated (the so-called "deadly toilet spider" was an elaborate hoax.) Most exotic spiders will be so small or obscure that they will probably not even be noticed except by experts!

Literature Cited

Bristowe, W. S. 1931. A preliminary note on the spiders of Krakatau. Proc. Zool. Soc. London 1387-1412.

Culin, J. D., and K. V. Yeargan 1983a. Spider fauna of alfalfa and soybean in Central Kentucky. Trans. Kentucky Acad. Sci. 44: 40-45.

Culin, J. D., and K. V. Yeargan 1983b. Comparative study of spider communities in alfalfa and soybean ecosystems: Foliage-dwelling spiders. Ann. Entomol. Soc. America, 76:825-831.

Culin, J. D., and K. V. Yeargan 1983c. Comparative study of spider communities in alfalfa and soybean ecosystems: Ground-surface spiders. Ann. Entomol. Soc. America, 76:832-838.

Edwards, J. S. 1986. Derelicts of dispersal: Arthropod fallout on Pacific Northwest Volcanoes. pp. 196-203 in: W. Danthanarayana (ed.) Insect Flight: Dispersal and Migration. Springer-Verlag, New York.

Foelix, R. F. 2011. Biology of Spiders, 3rd edition. Oxford University Press, New York.

Richman, D. B., J. J. Ellington, K. R. Kiser, and G. F. Fabion. 1990. A comparison of New Mexico alfalfa spider fauna with Eastern andCalifornia faunas. Southwest. Entomol. 15:387-397.

Riechert, S. E., and L. Bishop. 1990. Prey control by an assemblage of generalist predators: spiders in a garden test system. Ecology 71: 1441-1450.

Wise, D. H., 1993. Spiders in Ecological Webs. Cambridge University Press, Cambridge, UK.

Young, O. P. and G. B. Edwards. 1990. Spiders in the United States field crops and their potential effects on crop pests. J. Arachnology 18:1-27.