Spider Myths and Misconceptions
Published on May 19, 2014
Spiders: Love them or hate them, a lot of what you think you know about them is probably not true. We talked to Rod Crawford, curator of arachnids at the Burke Museum in Seattle and creator of a website about spider myths, about some common beliefs that are wrong — or almost right — in interesting ways. Here's what we learned.
Spiders Don't Want to Get Swallowed
It's often claimed that everyone swallows some number of spiders in their sleep — four per year, eight per year, 20 in your life. But in all the years of people contacting him through his website, Crawford has never collected a single verified case. And looking at it from the spider's point of view, it's unlikely that one would ever get anywhere near a sleeping person's mouth. Although house spiders are attracted to moisture — that's why you find them in sinks and bathtubs — Crawford says, "They're not so desperate for water that they would do what for you and me would be the equivalent of crawling up to the mouth of Godzilla."
In fact, spiders have every reason to avoid a sleeping person entirely. Their eyesight can't perceive something as huge as a human. "But they do have very good instincts for avoiding an early demise," he says, "and one of those involves steering strictly clear of anything that's making gigantic vibrations."
While you sleep, your heart, pulse, breathing — and possibly snoring — all create vibrations that can be detected by spiders. "Vibrations are an immense part of the spider's sensory universe," Crawford says. "It's how they detect their prey, and it's how they detect predators and other dangers."
Spiders Hardly Ever Bite
Even people who aren't terrified of spiders seem to think that spider bites are common, but there's every reason to think that spiders hardly ever bite people.
"Real spider bites do occasionally happen, but as far as I can tell, they've got to be really rare events," he says. "Using myself as a guinea pig, in the course of my long career, I have handled tens of thousands of live spiders with my bare hands. In the course of all that, I have received two genuine spider bites, both trivial in their effect."
Science confirms Crawford's experience. In one study, scientists studying hobo spiders in Oregon could locate only 33 cases of bites in three years. Another spider expert who did some math determined that these findings means an Oregonian is about 4,000 times more likely to be in a car crash than to be bitten by a spider. And in another study, researchers collected 2,055 brown recluse spiders from a single home in Kansas — none of whose residents were ever bitten.
Most Spiders Don't Leave Obvious Puncture Marks
Some people are sure they can tell a spider bit them because it leaves two puncture marks. "That means everyone who's bitten twice by a flea or bedbug is sure they have a spider bite," Crawford says.
The myth is based on fact: Spiders do have two fangs. But whoever came up with the idea got something else wrong: "What they didn't know was that spider fangs are so incredibly slender that the punctures are essentially invisible," Crawford says.
There's one common species with fangs large enough to leave puncture marks about half the time, he says, but for the rest — even tarantulas — you're not going to see the marks.
Misdiagnosed Spider Bites Are the Real Problem
In fact, no one — not a doctor or even a spider expert — can tell whether something is a spider bite by how it looks. If you didn't catch the spider in the act, the only way to tell for sure is by a specialized lab test. So if your doctor says something looks like a spider bite, you may want to ask whether it could be something else.
Serious, potentially fatal conditions can be misdiagnosed as spider bites. "MRSA can kill you, and it's one of the commonest things that is mistaken for spider bites," Crawford says. "There's an even worse bacterial skin infection called necrotizing fasciitis that can kill you really fast. And then, of course, there's skin cancer."
Spiders Are Almost Always Nearby
The person who tells you about all the spiders you've swallowed probably will also delight in informing you that you are always within 3 feet — or some other number — of a spider.
They may be wrong again, but not in the way some of you are hoping.
"If you're in a natural habitat, like a forest or a meadow or even your lawn, you're almost certainly much closer than 3 feet to a spider," Crawford says. "In all likelihood, there are spiders directly under your shoes and within 3 centimeters of you on all sides."
However, if you're sitting inside at your computer, as you might be if you are reading this, he says, "there may be a spider within 3 feet, or it may be as much as 20 feet away."
That's a relief — wait, there are spiders that close inside a building?
Yes, absolutely. "There's no house without house spiders. Unnatural environments have existed for long enough that a number of spider species have undergone adaptive shifts and become house spiders," he says.
Crawford explains that many species had habits that made it easy for them to move in with us. Spiders that lived in the cracks in rocks or cliffs found a similar habitat in stone or brick buildings, and those that lived in the crevices of tree bark found themselves at home in wooden houses.
"There are probably at least five or six species in any given house," Crawford says. "In Seattle, there are about 20 or 30 species that are commonly found with indoor populations."
Spiders Won't Thank You for Evicting Them
So while you may think you're doing a good deed when you put a spider outside instead of killing it, you're really throwing it out of its home. "My guesstimate is that 95 percent of the spiders in a given building were hatched there," Crawford says.
If you're less kindhearted and try using pesticides instead, you're wasting money. "Pesticides are all formulated with insect physiology in mind," he says. But remember: Spiders are not insects. They're not even very closely related — perhaps no more closely related than, say, birds and frogs.
So while a pesticide will kill a spider by direct contact, it won't have the residual effect that it has on insects. "And if you're just going to use it to kill the spider you can see, why not just step on it? At least that doesn't pollute anything," Crawford says.
If it bothers you to see spiders, he says the best solution is to reduce the number you actually see. "Seal up all the gaps and cracks and holes that they use to wander out from their part of the building to your part of the building. Every place a pipe comes out of the wall, stuff rags around it. Every door that has a half-inch gap, weather-strip it."
When you take those actions, remember that most of the spiders are not visitors. "Weather-strip under the door to the garage and the door to the basement, and that will keep more spiders out of your living room than weather-stripping under the door from the outside."
Yes, the spiders will still be living in the wall and floor voids and crawl spaces — but, hey, out of sight, out of mind, right?
Try to Love Them — or At Least Appreciate Them
Spiders do a lot of good. "Spiders are of absolutely crucial importance to all land ecosystems because they are the leading predators of insects," Crawford says.
Think of how many spiders are close to you in that meadow, he says: "They all have to be eating something." So, just think of how many insects there are, and imagine what would happen if the spiders were gone.
"Suppose some arachnophobe had a magic wand and could wave it and make all the spiders disappear," Crawford says. "Now think of footage you've seen of a locust plague. What if tens of thousands of insect species did that because they had no predation control?" In comparison, spiders don't sound so scary after all, do they?