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Big List of Spiders

Ready, set? By the end of 2005, a new list of spiders found in five Great Lakes states will be posted on the Web for all to scrutinize. Petra Sierwald, assistant curator of insects at The Field Museum, and two colleagues combed through existing records to determine how many species of spiders have been recorded in Wisconsin, Michigan, Ohio, Indiana, and Illinois. By the end, she had included 900 species. Illinois scored the highest number with 622 recorded species.

Why produce such a list? “If we have enough lists around a state you can begin to predict what you are likely to find,” Sierwald said, “and then you can know what to look for. Spider fauna are a good proxy for biodiversity in general because they prey upon different types of insects,” Sierwald noted, “so a large diversity of spiders means a larger biological diversity in the area.” Spiders are the largest group of animals made exclusively of predators.

In a paper to be published in the Proceedings of the Indiana Academy of Science, Sierwald and co-authors note that Chicago Wilderness is an especially hot spot for sheet web spiders, those arresting creatures creeping toward three millimeters in size. “No one would have thought this!” she said. But Michael Draney from the University of Wisconsin–Green Bay’s Cofrin Center for Biodiversity is an expert in those species and found a surprising number in the species lists.

Interestingly, the number of spiders on the list may not reflect the actual biodiversity so much as the degree of attention an area has received from spider experts. Joe Beatty, a spider expert at Southern Illinois University, recorded a lot of spiders over the years; hence Illinois’ high ranking on the list.

— Debra Shore