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Myths about "Dangerous" Spiders

Myth: People have lost arms and legs because of spider bites.

Fact: Probably everyone who reads a lot of newspapers has seen one of these stories, which crop up every few years. There is rarely a real spider associated with such cases, which basically result from physicians' near-total lack of spider training and from the news media's love of "scare stories."

I don't have full details of cases that happened in other parts of the country, but it is certain that spiders did not cause the two most notorious cases in Washington State. In one case in the late 1980s, an unknown spider bit a man working under a filthy derelict car in Morton, Washington. Becoming ill, he was rushed to Harborview Medical Center in Seattle, where eventually an arm was amputated. All the local media blamed the spider with great gusto. None of them published any correction when lab work revealed that the puncture had become infected with Clostridium perfringens, a gangrene-causing bacterium, and the man's symptoms were not caused by the spider venom at all.

On January 1st, 2001, a man in Mount Vernon, Washington woke up with one of those "mystery bites." The man was apparently already under treatment for some condition that compromised his immune system. The man's doctors (who, as usual, knew nothing of spider geographic distribution) immediately blamed the mythical "brown recluse" spider for the resulting illness. Later they backtracked and started blaming the hobo spider, which at least occurs in the area -- but not at that season! It is simply not possible that either species was present at the time and place when the man received his "bite." My belief is that the subsequent bilateral amputation had nothing to do with the "bite." But spiders cannot be sued for malpractice and cannot sue for defamation of character, so they make convenient scapegoats. One newspaper used the remarkably foolish headline "Spider takes legs of Skagit County man."

Myth: Spider "infestations" should be controlled with pesticides.

Hobo spider trap      photo courtesy            hobospider.com

Fact: Where to begin? Since spiders are predators, they don't infest anything. Apparent sudden increases in population are really just temporary increases in activity, usually connected with mating. Since nearly all spiders are harmless and beneficial, it doesn't make much sense to talk about "controlling" them; the spiders themselves are the best pest controllers!

If for some hard-to-imagine reason a situation really does arise where spiders must be eliminated from an area, pesticides are definitely not the way to go. An honest, properly trained exterminator will tell you this, but there are far too many who are trained only in how to market and apply pesticide treatments. Spiders do not react as strongly to "residual" insecticides as insects do; these chemicals will kill the spiders contacted directly by the spray, and that's about all. Spiders are highly mobile and quickly repopulate any area from which they have been eliminated. And spider egg sacs are relatively impervious to pesticides.

Sticky traps (right) remove many more spiders than typical pesticide treatments, and have the added advantage of neither polluting the environment nor making your home toxic. But an even better technique is to physically exclude spiders from the space where you don't want them, by sealing gaps, cracks and openings of all kinds.

Text © 2003, Burke Museum of Natural History & Culture, University of Washington, Box 353010, Seattle, WA 98195, USA Phone: 206-543-5590 Photos © as credited

Queries to Spider Myths author, Rod Crawford This page last updated 1 September, 2010 This site best viewed at 800 x 600 using IE 5.0 or above.