Hobo Spiders, Part 3 of 4

Black Widow Spider (Photo by Hodari Nundu)

(The Book of Deadly Animals hits the US later this month. As with the recent UK release of the book, I'm going to celebrate by running here an expanded version of a story from the book.)


It used to be said that no US spider was really dangerous,and this view held sway well into the 1920s, despite well-attested reports ofdeaths from the bites of widow spiders. It was only after intrepid biologistslike William Baerg and Allan Blair subjected themselves to widow bites in thelab, and suffered horribly, that the prevailing opinion changed. It took thirtymore years for scientists to sort out the two syndromes apparently caused bywidow bites—one featuring extravagant pain spreading rapidly throughout thebody, the other the slow death of the flesh around the bite. Eventually it wasdemonstrated that the second syndrome should have been blamed all along on theunobtrusive recluse spiders.
That ought to clear everything up, but it hasn't.Specialists are routinely annoyed by pseudofacts claiming that the averageperson inhales four spiders per year in his sleep or that recluse bite symptomscan be cured with tazers. Many myths mix in a pinch of reality. The blushspider, for example, must have been inspired by the widow, which used to infestoutdoor toilets and bite people in the genitals. And the false reports of camelspider venom read like an exaggerated account of the true effects of reclusevenom.
It's taken a long time to sort out the truth behind hobospider bites. They produce symptoms similar to those caused by recluse venom,but they occur in areas outside the recluse's range—the Northwest quadrant ofthe US and adjacent parts of Canada. After the brown recluse's danger came topublic attention beginning in the 1950s, doctors in the Pacific Northwest beganto diagnose certain lesions as recluse bites. But these diagnoses didn't fitthe known range of the recluse. No member of its genus is regularly found inthe northern half of the US.
In the early 1970s, this mystery came to the attention oftoxinologist Darwin K. Vest, an autodydact whose work on cobras, rattlesnakes,and other venomous creatures had won him respect in scientific circles. Whileworking at Washington State University's Pullman campus, Vest learned that thezoology department there often received queries about "necroticarachnidism"—flesh-killing lesions apparently caused by spider bites. Vesttackled the problem by looking into the cases of 75 patients in the PacificNorthwest diagnosed with this affliction. He exonerated spiders in most ofthese injuries, blaming them on insect bites, cigarette burns, and othercauses. Vest surveyed the homes of 22 remaining patients. Collecting by handand with sticky traps, Vest and his team collected thousands of specimens. Noneof the homes yielded recluses, but sixteen of them revealed healthy populationsof the hobo spider. Sometimes a single sticky trap measuring about 15 by 30 cmwould fill with hobos overnight.
The presence of hobos in such numbers was suggestive, but itproved nothing. The average home in any temperate region is likely to hostseveral dozen species of spiders. Most people don't realize that they spendevery day of their lives close to spiders, so that seeing one the same day youget a bite or scratch proves nothing.
Vest decided to bring hobo spiders, and several othersuspect species, into the lab for tests. He and his team milked live spiderswith mild anesthesia and micro-pipettes under a dissecting microscope, workingcarefully so that the spiders could be released unharmed. The spiders were sosmall that the capillary action of the pipettes was often enough to draw venomfrom the fangs. When that technique didn't work, the researchers sometimes resortedto mild electric shock, using a nine-volt battery to make the venom glandscontract and prompt the release of a droplet or two. Since each spider producedonly a miniscule amount, the researchers had to milk a great many to obtain aworkable sample. Their result: The hobo spider venom produced necrotic lesionsin rabbits. To confirm this result, Vest shaved the backs of rabbits and held ahobo spider down on each bald patch, forcing a bite. The lesions that formedwere similar to those found in human victims.