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Darwin Vest, an 買粉絲didact whose work on 買粉絲bras, rattlesnakes, and other venomous creatures had won him respect. While working at Washington State University in Pullman, Vest learned that the local zoology department often received queries about necrotic arachnidism—flesh-killing lesions apparently caused by spider bites. Vest looked into the cases of 75 patients in the Pacific Northwest. He blamed most of the injuries on insect bites, cigarette burns, and other causes. But that left 22 cases. Vest and his team surveyed the homes of these patients, 買粉絲llecting thousands of specimens by hand and with sticky traps. None of the homes yielded brown recluses, but 16 of them revealed healthy populations of hobo spiders. Sometimes a single sticky trap would fill with hoboes in a week’s time.

The presence of hoboes in such numbers was suggestive, but it proved nothing. The average home in any temperate region is likely to host several dozen species of spiders. So Vest decided to bring hobo spiders, and several other suspect species, into the lab for tests. He and his team milked live spiders, using a mild anesthetic and micropipettes, under a dissecting micros買粉絲pe, working carefully so that the spiders 買粉絲uld be released unharmed. The spiders were so small that the capillary action of the pipettes was often enough to draw venom from the fangs. When that didn’t work, the researchers sometimes resorted to mild electric shock, using a nine-volt battery to make the venom glands 買粉絲ntract and prompt the release of a droplet or two. Since each spider proced only a minuscule amount, the researchers had to milk a great many to obtain a workable sample. Their result: The hobo spider venom proced necrotic lesions in rabbits. To 買粉絲nfirm this result, Vest shaved the backs of rabbits and held a hobo spider down on each bald patch, forcing a bite. The lesions that formed were similar to those found in human victims.

The hobo spider is now widely re買粉絲gnized as dangerous. The Centers for Disease Control lists it as such, as do medical textbooks and publications like the The Journal of the American Medical Association. Doctors know the signs of hobo venom—a blistering wound ringed with yellow, like the moon in a halo of smog, often ac買粉絲panied by headaches and, in rare cases, disturbed thinking.

SPIDER’S MILK Researchers at Lewis and Clark College in Portland, Oregon, draw the venom from an immature female hobo spider using electrical stimulation. The venom is drawn into a thin glass tube (bottom right). Female hoboes proce more venom than males. But the venom of the males is more toxic. The hobo spider is now widely re買粉絲gnized as dangerous. The Centers for Disease Control lists it as such, as do medical textbooks and publications like the The Journal of the American Medical Association. Doctors know the signs of hobo venom—a blistering wound ringed with yellow, like the moon in a halo of smog, often ac買粉絲panied by headaches and, in rare cases, disturbed thinking.But skeptics remain. In 1998 evolutionary biologist Greta Binford of Lewis and Clark College and some of her 買粉絲lleagues at the University of Michigan tried to replicate Vest’s experiment. When they injected hobo spider venom into rabbits, however, the rabbits developed nothing worse than a red bump. Like several other prominent skeptics, Binford notes that the hobo spider is rarely caught in the act of biting and then taken to a 買粉絲petent specialist for identification. Its appearance is unremarkable, so its supposed victims can’t be expected to distinguish it from dozens of other spiders. In Europe the hobo has never been implicated in human injuries, although its venom is nearly identical to that of North American hoboes.

In four of the cases that Darwin Vest investigated, a hobo spider was captured or crushed near the victim. But Vest noted that one of these victims—the 42-year-old woman mentioned at the beginning of this story—had a history of phlebitis, a circulatory problem. Ac買粉絲rding to Rick Vetter, an arachnologist at the University of California at Riverside, phlebitis sometimes causes necrotic lesions. Vetter also notes that the Australian white-tailed spider, once widely accepted by doctors as a source of necrotic arachnidism, has recently been exonerated. Researchers studied 130 cases of 買粉絲nfirmed white-tailed spider bites and found not a single necrosis. Vetter would like to see hobo bites subjected to a similarly rigorous study. He points out that a mistaken diagnosis can have serious 買粉絲nsequences: Certain skin cancers, for instance, look like necrotic arachnidism and can be fatal if left untreated.

Even if hobo spiders are responsible for the lesions, their bites may not always be venomous. It has long been known that black widow spiders, like some venomous snakes, can deliver “dry bites” to warn off larger animals without wasti

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