Arachnophobia And Why You Should Get Over It

Explanation: There I was, in an cold early spring afternoon the pine forests of northern Arizona, turning over logs and peeking under tree bark, looking for lizards ... when suddenly I uncovered this defiant mom and her kids.

Probably a family portrait here, with the large mom
watching her kids, and the (usually) tinier dad (upper left)
leaving the scene ...

Although as a wildlife ecologist, I seek rather than shun such critters, I can appreciate how much of the non-biologist world may suffer from some degree of arachnophobia. Spiders are other-worldly, with their eight eyes and eight legs and fangs and spinnerets weaving strands of spider silk. Even their skeleton, like that of all arthropods, is on the outside of their body. Shudder! Jump back!

But consider the amazing diversity of spiders -- with about 38,000 species described worldwide -- and the key roles they play in the natural world.

Spiders may be major predators of pest insects including moths, mosquitoes, flies and others, keeping their populations in check. As the density of prey increases, spiders continue to space themselves, thereby maintaining stable population densities (Riechert 1974).

In a study of predatory spiders in Britain, Nyffeler (2000) estimated that spiders in agricultural lands kill approximately 0.9 to 36 pounds of insects per acre (1-40 kg per ha) each year. With about 42 million acres (17.1 million ha) of agricultural land in Britain (United Kingdom), this translates to about 28 to 1,500 million pounds, or 14,000 to 750,000 tons (17.1 to 684 million kg) of insects consumed by Britain's spiders every year. This is equivalent to as much as 16,536 Boeing 737 airplanes!

And this is just in Britain. Consider the vast agricultural areas of the world, never mind all the forests and the human habitations and gardens in which spiders play this ecological role of pest controller.

Spiders also seem to be able to control populations not just of insects but also centipedes (Clarke and Grant 1968). Wolf spiders have been shown to consume harmful aphid pests in wheat fields of Switzerland (Nyffeler and Benz 1988). Other studies confirm the beneficial advantages of our octo-legged friends.

For this reason alone, spiders are inappropriately maligned and feared. And this is why you should get over your arachnophobia.

Information:
     Clarke, R.D. and P.R. Grant. 1968. An experimental study of the role of spiders as predators in a forest litter community. Part 1. Ecology 49(6):1152-1154.
     Nyffeler, M. 2000. Ecological impact of spider predation: a critical assessment of Bristowe's and Turnbull's estimates. Bull. Br. Arachnol. Soc. 11(9):367-373.
     Nyffeler, M., and G. Benz. 1988. Feeding ecology and predatory importance of wolf spiders (Pardosa spp.) (Araneae, Lycosidae) in winter wheat fields. Journal of Applied Entomology 106(1-5):123-134.
     Riechert, S.E. 1974. Thoughts on the ecological significance of spiders. BioScience 24(6):352-356.
     Wise, D.H. 1993. Spiders in ecological webs. Cambridge Studies in Ecology. Cambridge University Press, U.K.

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