Spiders in the House

Spiders in the house are almost always harmless predators that live quietly in corners eating insects, or wanderers that came in under a door. In the US only two groups, widows and recluses, are medically significant, and both are easy to tell apart from the common house species once you know what to look for.

Spider basics

Are spiders insects? No. Spiders are arachnids, a class that also includes ticks, mites, harvestmen and scorpions. The quick check:

Are spiders bugs? In casual speech, yes; to an entomologist, "bug" means true bugs (Hemiptera), and spiders aren't those either.

How many legs do spiders have? Eight. The short leg-like pair at the front are pedipalps, used for handling food and, in males, mating. (Eight legs alone don't make a spider: all arachnids have them.)

How many eyes do spiders have? Usually eight, arranged differently in each family. Recluses have six; some have fewer.

How long do spiders live? Most house and garden spiders live about a year. Cellar spiders and funnel weavers can reach two or three, brown recluses 2–4, and some female tarantulas pass 20.

What do spiders eat? Insects and other arthropods, including flies, mosquitoes, moths, roaches, crickets and other spiders. They inject venom and digestive enzymes and digest prey outside the body; the Burke Museum notes they consume solids this way too, not just "juices."

Do all spiders make webs? No. All spiders make silk, but only about half the species build webs to catch prey. Wolf spiders and jumping spiders hunt on foot.

Do spiders poop? Yes. They excrete a mix of liquid and solid waste that leaves small dark or white drips on walls and windowsills below where they sit.

How do spiders mate? The male spins a small sperm web, loads sperm into his pedipalps, then courts the female with vibrations, dances or gifts. Females eating males is far less common in nature than legend says; even for black widows it was mostly seen in lab cages.

Can spiders hear? They have no ears, but fine hairs on their legs detect air vibrations, and some spiders sense sound through their webs.

Do spiders sleep? Not like mammals, but they have daily rest periods with very little activity.

How many spiders do you eat in your sleep? None to speak of. The Burke Museum, which collects spider myths, found no case in the scientific or medical literature and no credible eyewitness account. A sleeping person's breathing, heartbeat and warmth are vibrations spiders avoid.

Common house spiders in the US

The Burke Museum notes a typical home holds 10–30 spider species, most of them never noticed.

For photos and ID tips, see house spiders and types of spiders.

Joro spiders

The Joro spider (Trichonephila clavata), an East Asian orb weaver first found in northeast Georgia in 2014, has spread through Georgia, the Carolinas, Tennessee and neighboring states, largely by hitching rides on vehicles. Females are large and yellow, blue-black and red, with big golden webs on porches, fences and power lines. They're shy, their venom is weak, and they rarely come indoors.

Water spiders

"Water spiders" usually means fishing spiders (Dolomedes): large brown spiders that run on the surface of ponds and docks. They look scary but are harmless and occasionally wander into lake houses.

Which spiders are dangerous?

Two groups in the US:

• Widow spiders (Latrodectus): shiny black (or brown) with a round abdomen and a red-orange hourglass. Neurotoxic venom. See black widow.
• Recluse spiders (Loxosceles): tan, violin mark, six eyes; mainly south-central US. Tissue-damaging venom. See brown recluse.

Even these rarely cause deaths: Poison Control found no deaths among more than 15,000 US black widow cases it reviewed. Hobo spiders were once blamed for wound-causing bites in the Northwest, but current research doesn't support that. See dangerous spiders and spider bites.

Why there are spiders in your house

Most people assume spiders come inside to escape the cold in fall. The Burke Museum's arachnologists say that's mostly a myth:

• House spiders are indoor species. Most spiders living in homes are a small group of species adapted to buildings; the Burke estimates fewer than 5% of indoor spiders have ever been outdoors. Most outdoor spiders that do get in die or fail to breed.
• Late summer is mating season. The sudden crop of big spiders on floors in August and September is mostly adult males wandering in search of females. Females and young stay hidden in crawl spaces, storage areas and wall voids.
• Food draws them. More insects (from lights, moisture, crumbs or a pest problem) means more spiders. UC IPM and NPIC both recommend cutting the insect supply first.
• Gaps let wanderers in. Ground hunters like wolf spiders do walk in under doors without sweeps, through torn screens and around pipes and vents.

Spiders don't come up through drains; one in a tub came down the wall looking for water and can't climb the slick sides.

What eats spiders?

Birds, lizards, geckos, toads, centipedes (including house centipedes indoors), and wasps such as mud daubers and spider wasps. Spiders are also major predators of each other.

Spider webs and what they tell you

You can often name the spider from its web. Messy 3D cobwebs in corners and windows belong to the common house spider; loose, floppy webs high in basements to cellar spiders; flat sheets with a funnel to funnel weavers; and wheel webs outside lights to orb weavers. Dusty, abandoned cobwebs are old silk that collected lint, not proof of a current infestation. Low, tough, tangled webs near the ground in garages and woodpiles are where to look for widows.

Do spiders bite people?

Almost every spider has fangs and venom, but most can't pierce human skin and the rest bite only defensively. UC IPM notes that many skin lesions blamed on spiders have no proof a spider was involved, and bites from fleas, bed bugs, mosquitoes and other insects are often mistaken for spider bites. If you're waking up with new bites, a spider is the least likely explanation. See spider bites.

What people dealing with house spiders say

From r/pestcontrol and r/HomeImprovement:

• "Spider bites" in bed usually aren't. One person sure that house spiders were biting him every night put out glue traps and caught just two spiders. Pros in the thread urged a bed bug inspection, since spiders don't repeatedly bite sleepers.
• Lots of spiders means lots of prey. Technicians regularly point out that a house full of spiders has an insect problem: flies, crickets, roaches, even scorpions. Fix that and spiders drop off.
• Sealing beats spraying. Homeowners who kept finding spiders indoors found gaps around ceiling supply vents and attic openings; sealing them with low-expansion foam helped. Twice-yearly perimeter sprays get mixed reviews.
• Glue traps answer "how many?" Sticky traps along baseboards show which spiders you have and where they come in, before you spend money.

How to keep spiders out

1. Vacuum webs and egg sacs regularly, including corners, under furniture and around windows. UC IPM notes spiders often don't survive the trip through the hose.
2. Reduce clutter and store things in sealed bins, off the floor and away from walls.
3. Seal entry points: door sweeps, screen repairs, caulk around pipes, wires and vents.
4. Change outdoor lighting to yellow or sodium-vapor bulbs, or move lights away from doors.
5. Lower humidity in basements with a dehumidifier.
6. Keep vegetation, mulch and firewood away from the foundation.
7. Sticky traps in basements and garages, out of reach of kids and pets.

What doesn't help much: peppermint oil and other "natural" repellents (the Burke Museum notes there's no evidence spiders can smell them), ultrasonic plug-ins, and foggers. NPIC notes indoor insecticide sprays may not give long-term spider control. Most house spiders are best handled with a vacuum. Full guide: how to get rid of spiders.