| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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here at the academy SpidermanIn urban Los Angeles, where Charles Griswold grew up, the only wilderness an inquiring boy could explore was his backyard, and its only permanent wildlife were things that fly, crawl, and burrow. There are, after all, insects everywhere, and wherever there are insects there are spiders. Griswold developed an infatuation with arachnids that still holds him enthralled. As he prepared his master's thesis at the University of California at Berkeley on jumping spiders, he was unsure whether to seek a career in ecology or taxonomy. It was a trip to see the spider collection at the California Academy of Sciences that convinced him to choose systematics. "They were such beautiful animals," he says. "Perfect experimental tools for studies of behavior and biogeography." Insects and spiders are both arthropods--that is, they have jointed legs--but they are quite different. Apart from the extra pair of legs, spiders' bodies are made up of only two distinct parts, the abdomen and the head-thorax (rephalothorax), unlike the three parts of insects. In fact the common ancestor of these two orders lived at least 540 million years ago, in the ocean. Some of the earliest known fossils, from the Burgess Shale in British Columbia and China, which date from 500-600 million years ago, already show a clear distinction between the ancestors of spiders and insects. Griswold was especially intrigued by jumping spiders. They have quite elaborate behaviors, engaging in lively mating dances and a distinctive way of hunting. And their eyesight is excellent; they can recognize their own species on TV, and, depending on the gender of the image, attempt to court or fight in response. They use vision to stalk their prey, then pounce upon it "like a cat on a mouse," says Griswold. He became particularly interested in the genus Habronattus, and produced a cladogram which showed the historical relationships, or phylogeny, of its common ancestors. So accurate has that cladogram proved to be that Griswold's colleagues have been able to use it to predict behaviors, such as courtship dances, for various species. "Everything we know about evolution is summarized in the form of a phylogeny," says Griswold. "And all questions about evolution must be posed in the light of a phylogeny." Griswold's interest in evolution took him to Africa to survey the biogeography of the montane rainforests, those forests on the continent's cooler, upland slopes. Here, he untangles a history "told to me by spiders." They tell a tale of ancient forests, that have become isolated islands, each with its own unique assemblage of species. And they have been resilient over millions of years, even coping with large climatic variations during the Pleistocene without major evolutionary adaptation. It was deep in the forest of Cameroon that Griswold learned another rule about field research. Never forget your business cards. Gifts and speeches intended to convince the local chief that his pursuits were legitimate were making no impression. The chief pointed out that he governed at the people's pleasure and he couldn't afford to make a mistake. Only when Griswold was able to produce his business card showing he was a bona fide member of the California Academy of Sciences staff was the chief reassured. From jumping spiders, Griswold turned his attention to his present fascination, the orb-web spinners which produce perfectly symmetrical webs. From the vibrations an intruder creates on the orb-web spinners's web, a spider can usually recognize whether it has attracted a mate, a meal, or an enemy. It doesn't always work. Some orb-web predators lure the spider within reach by plucking the web threads in the same way as a potential mate. The exhibition "Spiders!", which opens at the California Academy of Sciences on August 23, was originally conceived at the Smithsonian Institution while Griswold was working there, and he was one of the scientists who reviewed many of the initial proposals. He had one overriding concern: "Don't dumb it down," he told them. They didn't. Visitors will discover what it's like to be a spider, view the world from a spider's perspective, and receive the sensory input, especially the vibrations, that a spider receives. They will also learn that there are spiders everywhere: on mountaintops and seashores, in deserts and skyscrapers, in fresh water and even drifting high in the upper atmosphere. Two things about spiders Griswold would like visitors to take away with them: One is the way spiders communicate ("almost as if they're speaking to one another"), especially their sexual prowess and receptiveness. The other is what they can do with silk. They can lasso prey, travel by bungee jumping, build barriers that hold back larger animals while expending the minimum amount of thread, establish an early warning system, and fool prey into thinking they are somewhere else. Besides the displays, the Academy's exhibit will feature live animals, from the giant bird spiders of South America to black widows you might find in your backyard. Keith K. Howell is Editor of Pacific Discovery. |
summer 1997
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