Think Before You Squash a Spider
Few creatures are as widely reviled as spiders. So perhaps it’s not surprising that the arachnophobic Little Miss Muffet is remembered with sympathy while her father, the 16th-century entomologist and physician Thomas Muffet, who adored the eight-legged creatures, is long forgotten.
But Thomas Muffet might be vindicated yet. Materials scientists, medicinal chemists and agricultural biotechnologists are increasingly looking to spiders as a potential source of super-fibers, medicines and insecticides.
“Spider webs are being studied by mechanical engineers because of their remarkable tension displacement qualities, and spider silk could replace some synthetic fibers, such as nylon, Dacron and even Kevlar for some applications,” said Mark S. Lacey, a Wilmington, Del.-based entomologist specializing in spider biology.
“Spiders have been used for medicinal purposes for centuries, and it’s looking like their venom may be able to prevent permanent brain damage in stroke victims,” he said. Spider venom also shows promise as a rich source of new insecticides, Lacey said.
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Earlier this summer, Australian scientists reported that they had determined the molecular structure of a nerve toxin in Australian funnel web spiders and showed it is a powerful insecticide with commercial potential with no effects on mammals.
And also earlier this summer, the U.S. Army, in collaboration with a biotechnology company, spun the first few inches of a new, genetically engineered spider silk using a gene from the golden-silk spider, Nephila clavipes, that had been inserted into bacteria.
Spider silk is one of the toughest substances known, and the Army wants to weave it into bulletproof vests and parachute cords. Others see potential applications, from bridge suspension cables to apparel.
“Everyone is desperate for spider silk in commercial quantities,” said Glenn Elion, a vice president of Agricola, a San Francisco-based company that cloned the spider gene used by the Army.
Warriors from the era of Genghis Khan wore arrow-blunting body armor made from leather and spider silk. Spider silk was used to make the cross hairs on Air Force bomb-targeting systems and optical instruments until the 1950s.
Dragline silk, the strongest of several kinds of spider silk, is not the strongest known fiber in terms of the force it can withstand when held in place. But it is exceedingly elastic, making it a material unrivaled in overall toughness. Scientists have calculated that a fiber the thickness of a pencil could stop a Boeing 747 in flight as easily as a strand of web stops a fly.
But it’s not practical to farm spiders for their silk as the Chinese do silkworms; their webs take up lots of space, they require live prey, and many are too aggressive to domesticate. So biotechnologists are turning to spider genes. Researcher Kenn Gardner has been leading DuPont’s efforts to study spider silk genes and fathom the molecular basis for spider silk’s unique properties.
DuPont has cloned parts of some spider silk genes and, like Agricola, is working with the Army to make homespun fibers. Both companies have inserted the genes into bacteria, which then make a gooey protein that, when purified, can be extruded or spun into spider silk.
Jean Herbert, of the Army Soldiers System Command in Natick, Mass., said the Army hopes to choose the best genetically engineered spider silk and then blend it with Kevlar, the synthetic fiber now used in bulletproof vests. “Maybe Kevlar, which is strong but brittle, and silk, which is pretty strong and also gives a lot, could be twisted into a yarn,” Herbert said.
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Glenn King, who led the recent work on toxins from funnel web spiders published in the July issue of Nature Structural Biology, said spider venom is loaded with potentially useful insecticides. Spiders are insect predators, he said, “so if you’re looking for something to kill insects, spider venom is a good place to start.”
The major chemical transmitter in insect motor nerves is glutamate rather than acetylcholine, used by human nerves, so many glutamate-blocking insect neurotoxins in spiders appear to be harmless in people. King wants to find the key part of the funnel web spider toxin he’s studying, and adapt it for use as a pesticide.
Spider venom’s ability to block glutamate might have medical applications, too, since glutamate in the human brain is responsible for much of the damage that follows a stroke, said Rosemarie Roeloffs, an arachnologist at NPS pharmaceuticals in Salt Lake City, which has studied the medical potential of spider venom for years.
“Spider venoms are complex mixtures of up to a hundred different compounds, and each compound has a different effect,” Roeloffs said. One component was recently found to have anticonvulsant activity, she said.
NPS hopes to make slightly altered synthetic versions, because synthetic variants might have greater therapeutic potential and because marketing studies show most people are appalled by the idea of eating something from a spider.
Miss Muffet would probably relate to that. History suggests her father ground up spiders and fed them to her and other patients when they were ill. That remedy was touted by Aristotle but remains unpopular, even among spider lovers. “If I were in Muffet’s house,” Lacey said, “I wouldn’t even sniffle.”
