A spider in your house may be there for one useful reason; what it is hunting

It may be an unpopular opinion for your weekend, but that eight-legged creature chilling on your bathroom ceiling in one corner is probably helping you in some way. Not some sentimental and flowery "nature heals" type of help, but a tangible and real good deed, without you having to pay a dime for it. In 2016, researchers from North Carolina State University did something no one may have done in the past: they scoured 50 ordinary homes in the neighborhood of Raleigh from room to room, counting every arthropod they could find.

As Matthew Bertone and his colleagues point out in their 2016 peer-reviewed paper titled “Arthropods of the great indoors: characterizing diversity inside urban and suburban homes,” published in the journal PeerJ, the researchers found a conservative estimate range of 32–211 morphospecies of arthropods per home, and spiders were among the four largest groups identified, alongside flies (Diptera), beetles (Coleoptera), and wasps and ants (Hymenoptera). Most of what they found weren't pests; they were the natural predators of pests.

So what is it actually hunting?


Spiders do not invade your house simply because they have a taste for your interior decoration; they come into your house because it provides them with a controlled environment in which they can eat continuously. Insects such as flies, moths, mosquitoes, silverfish, roaches, and even bed bugs: these are what they are after. You have a spider that is operating an extermination program round-the-clock, noiselessly, and with no use of chemicals, with some side effects that you will never get billed for.

Most people react to a spider's presence far more strongly than anything it's actually doing. It isn't interested in you; you're just a large, warm obstacle between it and dinner. In a 2017 analysis published in the journal The Science of Nature, Martin Nyffeler and Klaus Birkhofer combined data from 65 separate studies to estimate that the world's spiders kill between 400 and 800 million metric tons of insects and other invertebrates every year. To put that in perspective, that’s about the same ballpark as the total weight of meat and fish that humans eat in a year: a comparison the researchers themselves drew, because apparently even scientists like a mic-drop moment. The spiders in your walls may be a rounding error in that number, but they are part of it.

Nature's most specific hunter

A jumping spider found in East Africa, Evarcha culicivora, doesn't just eat any mosquito it finds; it prefers blood-fed female Anopheles mosquitoes, the species that transmits malaria, over other equally available prey. This is documented in a 2006 paper, "A Predator from East Africa that Chooses Malaria Vectors as Preferred Prey," published in PLoS ONE by Ximena Nelson and Robert Jackson. It can visually distinguish blood-fed from non-blood-fed females and actively targets them, tracking a specific disease vector rather than hunting indiscriminately.

A faie caveat

None of this means that every spider in your house is a hero, or that you owe it a name or a recommendation letter. Some species really don’t belong inside; some can deliver a bite that’s worth taking seriously, and no one is obligated to live with something that makes their skin crawl. Comfort in your own home is a legitimate priority, not a character flaw. There’s a reason why the pest-control industry exists and on such a large scale.

However, that reflexive, screaming, shoe-first reaction most of us have is out of proportion to the real risk and might've been inherited mostly from the movies, not entomology. So next time you see a spider doing absolutely nothing in the corner of a room, maybe don't evict it right away. It’s not there for you. It’s working on the clock, doing work you didn’t have to advertise for, and its next target is probably something you’d have paid to get rid of anyway.