Editor’s Note: This article was reprinted with permission from Techletter, a biweekly training letter for professional pest control technicians from Pinto & Associates.
Spiders are unfairly implicated by doctors and laypeople alike for attacks on humans, but spider bites rarely happen for a variety of reasons including:
Spiders don’t gain any benefit from biting people
Biting a person does not benefit a spider, it only wastes precious venom. Our other biters (mosquitoes, ticks, chiggers, bed bugs) bite us because our blood or other fluids supply them with food. Spiders have no interest in our fluids; they feed on insects or other arthropods. Spiders bite people only in defense and even that rarely happens. When spider bites occur, it’s usually because someone reaches into an old boot or other little-used object where a spider has been hiding. The spider bites only as it is about to be crushed. Lest you think spiders are hanging around, waiting to bite at the drop of a hat, consider this: In a Kansas study of brown recluse spiders, 2,055 brown recluses were collected from one home during a six-month period...yet not a single occupant was bitten!
Most spiders couldn’t bite people even if they wanted to
Of approximately 3,000 different spiders in the United States, only a small number have fangs long enough and strong enough to break skin. Of those biters, the Centers for Disease Control considers that only two have truly dangerous bites: the brown recluse spider and the black widow spider. In fact, the hobo spider was recently removed from CDC’s venomous spider website. And very few spiders have bites that cause serious illness. Widow spiders have a neurotoxic venom that can cause serious illness, while the brown recluse spider is blamed for necrotic (open, ulcerated, slow-healing) bite wounds. Although very few spiders produce bites that result in a necrotic lesion, physicians, especially, continue to wrongly blame spiders for such wounds. Brown recluse spiders, in particular, are often wrongly blamed. These spiders are shy and rarely bite. Their bites usually heal on their own but can sometimes result in a necrotic bite. In Australia, a study of 750 verified spider bites from a number of different species, found that none of them resulted in a necrotic lesion.
Not every part of the U.S. even has dangerous spiders
It has been estimated that 60% of alleged brown recluse spider bites occur in areas where no brown recluse spiders are known to exist. In Florida, during a six-year period, 720 alleged brown recluse spider bites were reported, while during that same period, only five brown recluse spiders were confirmed in the entire state! People, including physicians, pay little attention to the actual geographic range of brown recluse and other spiders. You’ll occasionally hear the claim (maybe you’ve even made it yourself) that, even though brown recluse spiders (and more recently hobo spiders) don’t occur in a certain area, they could have been transported there in household belongings, in vehicles, or in landscape materials. Spider experts say that even if a brown recluse (or two or three) does find itself imported into a region, given the infrequency of brown recluse bites, the statistical probability that this imported spider would actually bite someone is almost zero. Yet physicians get claims of brown recluse spider bites all the time, and almost always, the victim never saw the offending spider.
About 80 percent of spider bite diagnoses are wrong
There are many medical conditions that are easily misdiagnosed as spider bites, and there are a number of other arthropods whose bites are blamed on spiders. In one study of 600 suspected spider bites in Southern California, 80% were caused by other arthropods, mostly ticks and conenose bugs. Physicians are probably the worst offenders. If the patient implicates a spider and the skin lesion looks like it could be a bite, the doctor usually pronounces it a spider bite, prescribes ointment, and sends the patient home.
Show me the spider
Spider experts feel that the diagnosis of “spider bite” should only be made when a spider is caught in the act of biting, or is otherwise reliably associated with the wound. Identification of the spider by an expert is also important since there are nonpoisonous spiders that look very much like poisonous spiders, and vice versa. Without spider confirmation, the diagnosis of spider bite should not be considered.
There is one clue as to whether the bite is from a spider. A spider bite is distinguished by two small punctures, set close together, from the spider’s two fangs. Most insects leave a single puncture mark when they bite. However, once the bite becomes swollen, it’s no longer possible to see the puncture marks. Because spiders only bite once, a person with multiple bites was not bitten by a spider. Likewise, when there are multiple bites in the same house or other location, spiders are not the culprits.
The unfortunate outcome of misdiagnosed spider bites is that people with serious medical problems may go undiagnosed and untreated when the easier diagnosis of spider bite is made instead. There are at least 30 different medical conditions that can cause skin lesions and that have been misdiagnosed as spider bites, including herpes, bed sores, basal cell carcinoma, diabetic ulcers, and Lyme disease. Perhaps the most important recent bite confusion is with MRSA, a sometimes deadly staph infection that causes draining skin abscesses and is becoming increasingly common.
This doesn’t mean that people can’t be bitten by a spider. But they should understand that a spider bite is extremely unlikely and should first ask themselves “what else could it be?” instead of assuming it’s a spider bite.
The owners are well-known industry consultants and co-owners of Pinto & Associates.