8 Facts About the Misunderstood House Spider

If you have a house, you probably have house spiders. They might live in your attic, basement, or windowsills or brazenly inhabit your houseplants. But despite their reputation as creepy interlopers, most house spiders haven't simply wandered away from home: Our houses are their natural habitats.

Some think of spiders as insects, lumping them in with six-legged invaders like roaches or ants. But spiders aren't insects and don't want to raid our cupboards. Like their outdoor relatives that eat crop pests, house spiders want to quietly kill insects that covet our food. If anything, spiders are on our side.

A spider's docile and helpful nature may not help calm people with severe arachnophobia, but fear and respect aren't mutually exclusive. The more we know about these misunderstood housemates, the less fodder we have for misguided phobias. In hopes of clearing house spiders' names, here are eight interesting facts that might persuade you to put down the shoe, pick up a magnifying glass, and give peace a chance.

1. Humans and House Spiders Have History

Like all modern arthropods, the spiders in your attic may be descendants of 7-foot-long marine animals that lived 480 million years ago. True spiders evolved about 300 million years ago, so they pre-date dinosaurs, not to mention us. It may feel like spiders are encroaching, but they were here first.

Still, deferring to spiders on a camping trip isn't the same as sharing our homes with them. Does a spider's evolutionary seniority give her free rein over habitats built by and for humans? Maybe not, but ousting spiders from any house is a herculean task. They're stealthy and stubborn, and they've been living with us for a long time; many house spiders are now specially adapted to indoor conditions like a steady climate, sparse food, and even sparser water.

"Some house spider species have been living indoors at least since the days of the Roman Empire, and are seldom to be found outside, even in their native countries," writes Rod Crawford, curator of arachnid collections at the Burke Museum of Natural History & Culture in Seattle and noted debunker of spider myths. "They usually spend their entire life cycle in, on or under their native building."

2. Putting a House Spider Outside Could Kill It

Not everyone afraid of spiders hates them, so some people try non-lethal eviction processes. Perhaps the most common strategy for getting rid of spiders involves trapping them in a cup and releasing them outside, where they can presumably return to their natural lifestyle. This is a noble sentiment (and often requires quick reflexes), but as Crawford explains, it may not achieve the desired result if the arachnid is a true house spider.

"You can't put something 'back' outside that was never outside in the first place," he writes. "Although some house spider species can survive outdoors, most don't do well there, and some (which are native to other climates) will perish rather quickly when removed from the protective indoor habitat. You're not doing them a favor."

Generally, Crawford says, only about 5% of the spiders you see in a building have ever set foot outdoors.

3. Not All Spiders in Houses are House Spiders

House spiders typically colonize new buildings via egg sacs attached to furniture or building materials, but sometimes outdoor spiders wander inside. Many of these are spiders that eschew webs in favor of active hunting, like wolf spiders, and may be seen scampering across floors or walls. If you release one of these outside, you might be doing it a favor. Just be sure to let the right one out.

Crawford notes that suspected "wolf spiders" are often male European house spiders, which tend to roam around more than females. Although many house spiders weave webs, a few mix things up by actively hunting prey. It's not always easy to tell indoor and outdoor spiders apart, but it might help to study the eyes more than markings or other features. For example, common house spiders and American wolf spiders look similar, but you can distinguish them by the arrangement of their eyes.

4. Not All House Spiders Look Alike

To complicate matters further, house spiders come in many shapes and sizes. The types in your house depend largely on where you live, although humans have helped many species spread around the planet, especially those from Europe.

Parasteatoda tepidariorum, aka American house spider, is native to North America but now found around the world. This spider is one of the most abundant house spiders. Measuring four to eight millimeters long, these yellowish-brown spiders have a tall, round abdomen and two rows of four eyes. They build tangled webs, often both outside and inside a building, so evicting them may be harmless—and futile. On the bright side, they have relatively mild venom and bite humans only in self-defense.

Tegenaria domestica, aka domestic house spider, is native to Europe but has also become cosmopolitan with human help. It's a widespread species that first appeared at United States shipping ports in the 1600s, and is now found across most of North America as well as Europe and western Asia. It ranges from six to 12 millimeters in length, with a reddish-brown "head" (the cephalothorax) and a pale, speckled abdomen. This spider builds funnel-shaped webs and is known to prey on pest insects inside homes.

Steatoda grossa, aka cupboard spider, has similarly expanded far beyond its native Europe, including North America and Australasia. Varying in length from four to 11 millimeters, this spider is known for messy webs that contribute to indoor cobweb buildup. It's also one of several Steatoda species known as a "false black widow" because people commonly confuse it with that highly venomous spider. But, the American house spider doesn't have the black widow's red hourglass, and our harmless American spider friend's bite is more like a bee sting.

Other common house spiders include Badumna insignis (black house spider, native to Australia and New Zealand), Pholcus phalangioides (cellar spider, cosmopolitan), Cheiracanthium mildei (yellow sac spider, cosmopolitan), Eratigena atrica (giant house spider, Europe and North America), Eratigena agrestis (Hobo spider, Europe and North America), and Kukulcania hibernalis (Southern house spider, Americas).

5. Spiders Don't Use Plumbing to Sneak Inside

Since spiders are often found trapped in sinks or tubs, many people assume the arachnid's came in through the home's plumbing. But modern drains feature sediment traps that would prevent spiders from passing, Crawford points out. "I don't know of even one case where a spider was actually shown to migrate into a house through plumbing."

Instead, he adds, they probably got stuck while looking for water. "House spiders are thirsty creatures living in a very water-poor environment, and any that venture near a sink or tub with drops of water in it will try to reach the water, often by climbing down a wall. Once in the slick-sided porcelain basin, they are unable to climb back out unless a helpful human 'lends them a hand.'"

6. House Spiders Pose Very Little Danger

Spiders in general don't deserve their scary reputation. They rarely bite people, and when they do, most species' venom causes only moderate and short-lived effects (this is true for the vast majority of house spiders, which have no incentive to bite anything they can't eat unless they think it's a matter of life or death).

"House spiders prey on insects and other small creatures," Crawford writes. "They are not bloodsuckers, and have no reason to bite a human or any other animal too large for them to eat. In any interaction between spiders and larger creatures like humans, the spiders are almost always the ones to suffer."

7. In Fact, House Spiders Can Be Helpful

Since spiders generally are a potent defense against agricultural pests like aphids, moths, and beetles, house spiders offer similar benefits indoors, helping suppress insects so a home's resident doesn't need to use synthetic insecticides.

"Spiders feed on common indoor pests, such as roaches, earwigs, mosquitoes, flies and clothes moths," explains a fact sheet by Bayer CropScience. "If left alone, spiders will consume most of the insects in your home, providing effective home pest control." And by keeping these populations in check, spiders can even help limit the spread of disease carried by insects like fleas, mosquitoes, and cockroaches.

If you want to ensure your house spiders are pulling their weight, check in and under their webs to see what they've been eating. Many web-dwelling house spiders simply drop the remnants of their prey to the floor after eating, a habit that can make an annoying mess but also provide evidence of their contribution to the household.

8. There Are Humane Ways to Manage House Spiders

If you still can't stand house spiders, it's possible to keep them in check without losing your cool. Instead of resorting to pesticides, smashing, or other methods potentially lethal to the spider (like a vacuum cleaner), try to stay ahead of population booms by limiting suitable habitats. Check windows, eaves, and other popular spider hangouts, and remove any cobwebs you find. This probably won't eliminate your house spiders, but it might drive them to lower-profile haunts like a shed, garage, or crawlspace.

Sealing potential entry points may not affect house spiders, since they don't sneak in from outside, but it could limit incursions by other spiders. And if tight seals prevent insects from getting inside, they may indirectly reduce your house spiders by limiting their food supply. Various myths suggest house spiders are repelled by osage orange, horse chestnuts, or even copper pennies, but Crawford is doubtful.

In many cases, house spiders are like Michael Jordan: You can't stop them; you can only hope to contain them. So rather than trying to play defense against such a resilient force of nature, why not just sit back and marvel at them? It'll make life easier for everyone—except for that fruit fly buzzing around the kitchen.