Spider bites are an overrated menace

2008 February 3

By Tim Eisele
Article ID: 123

[Editor's note: Some of the external links in this article point to photos that may be disturbing to some.]

I’ve been noticing that when most people see a spider,the first thing they think is, “Is it venomous?” Pretty much every mention of spiders in the news or entertainment media implies that not only are spiders in general venomous but they’re intent on biting you. In North America every largeish, brown spider gets hysterically labelled a “Brown Recluse”, and every black, round-bodied spider is imagined to be a “Black Widow“. The general perception is that they would just as soon bite you as look at you. Worse yet, there’s even a whole song-and-dance about how “spider bites” turn into massive necrotic lesions, with the skin in the middle dying and sloughing away, and never healing on their own, and body parts are lost, and all that jazz.

That is just the general perception. Entomologists or arachnologists have painted a very different picture of spider bites. This is summed up in a nice article by a couple of Canadian entomologists explaining how people all over the world are convinced that necrotic lesions come from spider bites, even though the vast majority of the time they are caused by diseases like Leishmaniasis or bacterial skin infections. Surprisingly, they find claims of bites from brown recluse spiders to be common even in Canada, which is far outside the natural range of these arachnids.

A big problem with spider bites is that the diagnoses is often made solely on the flimsy logic of, “I have this injury that looks like a bite, and there are spiders in my bedroom.” Given how many other things exist that bite people (mosquitos, black flies, biting flies, bedbugs, fleas, chiggers, ticks, lice, certain types of assassin bugs . . . not to mention simple pimples, ingrown hairs, splinters, infected thorn wounds, you name it), pinning it on some hapless spider just because it happens to be around is kind of gratuitous.

An even bigger problem is that the average doctor never studied entomology, has no training in diagnosing spider bites, and wouldn’t know one if they saw one. So when a patient comes in, and says, “A spider bit me, right here! See?” the doctor has no reason to disagree, and so says, “Oh, sure, looks a lot like the other wounds that people told me were spider bites. Lot of that going around.” And then, he proceeds to treat it inappropriately as an effect of venom, when the vast majority of the time he should really be treating for infection. This is a serious issue, as can be seen from the list, compiled by Rick Vetter of the UC Riverside Department of Entomology, of conditions that have been misdiagnosed as brown recluse spider bites..

These include:

  • Staphylococcus infection
  • Streptococcus infection
  • Gonococcal arthritis dermatitis
  • Cutaneous anthrax
  • Warfarin poisoning
  • Infected herpes simplex
  • Chronic herpes simplex
  • Varicella zoster (shingles)
  • Sporotrichosis
  • Keratin cell mediated response to fungus
  • Lymphoma
  • Lymphomatoid papulosis
  • Focal vasculitis
  • Purpura fulminans
  • Thromboembolic phenomena
  • Polyarteritis nodosa
  • Warfarin poisoning
  • Lyme disease
  • Rocky Mountain Spotted Fever
  • Soft tick bites
  • Insect bites (fleas, mites, biting flies, etc.)
  • Poison ivy/poison oak
  • Chemical burns
  • Diabetic ulcer
  • Pyroderma gangrenosum
  • Pressure ulcers
  • Stevens-Johnson syndrome
  • Erythema multiforme
  • Erythema nodosum
  • Toxic epidermal necrolysis (Lyell’s syndrome)

Vetter also points out, as do the Canadian entomologists, that supposed “recluse bites” are frequently reported from parts of the country where the brown recluse does not even occur in the wild. He additionally found that in areas where the brown recluse is common, confirmed bites (where the spider is actually seen biting or leaving the actual bite site) are very rare. He even reports one case of a house in Kansas where 2,055 brown recluse spiders were collected (450 of them large enough to have bites that penetrate the skin), and yet the family of 4 living in the house (and their many pets) never showed any evidence of a bite over an 8-year period.

My own experience is this: I’ve never been bitten by a spider, and it sure isn’t for lack of opportunity (I regularly poke, prod, and pick up large spiders that I find around the place). I once asked over 200 people on an email mailing list if anybody had ever seen a spider actually in the act of biting them (or scurrying away from a bite), and exactly two could honestly confirm a bite. Both had been bitten on the hand by some unspecified large spider, one while unstacking firewood, and the other while poking around in a glove compartment of a car that had been stored in a barn for some months. One of the two people said the bite was nothing serious, while the other stated:

“I got a large welt, with a tail following the blood flow. It hurt a lot for a couple of days, but then the welt went away, although the bite wound remained for a month or so.”

The second account, even if it is an actual account of a spider bite, doesn’t sound like the person was reacting to a venom. When I get stung by insects that definitely do inject a venom (bees and wasps), the venom causes local, symmetrical swelling and it all goes away after a few days. The bite as described actually sounds more like a puncture wound which became infected, which I understand often does tend to propagate along blood vessels. Like any other skin puncture, bacteria could have been introduced under the skin producing an infection. A non-venomous bite that introduces bacteria into the skin could therefore easily cause such a reaction. And, in fact, this is the likely cause for reports that many large spiders, such as “hobo spiders”, have a dangerous bites. The thing to keep in mind is, that any puncture wound (whether it is a “spider bite” or not) is an infection danger, and should be cleaned and disinfected accordingly.

Spiders are getting a bad rap for very little cause and we really shouldn’t blame them for a bite unless it is a sure thing. Realistically, only the very largest spiders are even able to penetrate the skin, and even they will only bite in the rare circumstance where they are being captured or pinched. People who handle spiders regularly agree that it is difficult to get spiders to bite. While there are a very few, like Australian Funnel Web spiders and true Black Widows, that have actually toxic venoms that can cause poisoning, even these are pretty overrated and hardly ever kill anyone. The vast majority of even the largest spiders are nothing to worry about. They are, at most, minor pucture wound hazards, not major threats to life and limb. And the stories about “necrotic spider bites” are almost all exactly that . . . stories.

If you are still worried about spider bites, keep this in mind: the situation where spiders might sometimes bite is when you’re putting your hand into a tight space without knowing what’s in there. This is a recipe for all sorts of injuries (cuts, scrapes, punctures, crushing, getting stuck, etc.), all of which are much more likely than a run-in with a spider big enough to bite you. So don’t go sticking your hand into tight places without looking first, and you’ll save yourself from a lot more injuries than just spider bites.

So, to sum up:

  • Spiders are very unlikely to bite.
  • While bites can happen under very unusual circumstances, the venom of all but a very few spiders is not dangerous.
  • The rare occasions where a spider bite is actually medically significant is when the wound gets infected, the same as any other puncture wound.
  • A wound of the type that the general population tends to call a “spider bite” is almost never caused by a spider, but is much more likely to be due to any of dozens of other causes. Unless you actually see a spider in the act of biting you, don’t assume that a wound was caused by a spider.

Other articles related to this topic:

2008 October 19

I was just wondering how bad do the funnel web spider bites hurt and how can you tell if you were bitten by it?..and I am pretty sure that you would most likely be able to tell because of the pain..but waht about if you felt something and thought it was a bea or something like that..but waht if you are asleep and never notice..well than how could you tell if you were bitten. Also when you are bitten, about how bad does it hurt..like does it sting like a bea,or like something like an little insect biting you(were you feal a tingle usualy) or is it like one of those sudden itches where out of no where it almost seems to sting and as an reaction you scratch fast??…so yeah could you like e-mail me back about those answers??…thank you soooooo much.

P.S- the reason i want to know this stuff if because I am going to Australia in the summer.

2009 January 16
Anna permalink

I live in Southeast Texas and got bitten on the foot last summer by a spider. And it was my own stupid fault: I left my loafers outside one night and then slipped them on two mornings later without emptying them out first. Whoopsie.

To kyra:
From what I’ve heard, Funnel Web Spider stings hurt like hell and can cause tingling around the mouth and tongue, facial muscle twitching, nausea, vomiting, profuse sweating, salivation, and shortness of breath. In other words, it seems pretty plain that it’s a bit different from being stung by bee (unless you’re allergic to bees, of course.) No, you’re probably not going to die, unless you’re very very unlucky. Antivenom has been available since 1981.

2009 January 16

it’s good to know i don’t have to be worried about spiders. i’d like to see similar data about snakes if it’s true. i’ve considered moving to canada because of bugs and snakes.

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