Do Spiders Mean the House Is Dirty?

Spiders do not eat crumbs. They eat other invertebrates, and where those are is where they will be.

Which means a spotless house with a bright porch light, gaps under the doors and a damp basement will have more spiders than a cluttered one with none of those. Cleanliness is close to irrelevant except where it happens to correlate with something that matters.

What they are actually tracking

Prey. The whole of it. Flies, moths, mosquitoes, silverfish, ants, springtails, other spiders. Everything below is a proxy for this.

Humidity. Basements, crawlspaces, bathrooms. Cellar spiders in particular want damp.

Shelter. Undisturbed places to build and sit — wall voids, corners, under furniture, behind stored material.

Warmth, seasonally.

None of those is affected by whether the kitchen counters are wiped.

What increases the insect supply

Outdoor lighting near doors and windows, which is the single largest factor in most houses. A porch light draws moths and flies from a considerable distance, and they accumulate at the door and the windows every night — which is where the spiders then set up.

Switching to warm-toned bulbs, motion sensors, or moving the light away from the entrance reduces the insect load more than any indoor measure.

Gaps. Under doors, around service penetrations, in vents, around window frames. Every gap is an insect route.

Standing water and damp — a leaking tap, a blocked gutter discharging at the wall, a wet crawlspace.

Vegetation against the building, which is a bridge and a habitat.

Mulch and leaf litter against the foundation.

Where cleaning does help

Not nothing, but at the margins:

• Removing webs and egg sacs takes out the established residents and the next generation. This is the most direct thing indoor cleaning does.
• Reducing clutter in garages, sheds, lofts and cellars removes shelter — which matters most for the two groups worth caring about, since widows and recluses both want undisturbed voids at ground level.
• Vacuuming corners, under furniture and behind appliances, where webs go.

Notably, the places where cleaning does most are the ones people clean least.

Where clutter genuinely matters

For most spiders it does not. For widows and recluses it does, because both want exactly what a cluttered garage provides: dark, dry, undisturbed voids at ground level.

Stacked cardboard, stored timber, unused pots, boxes that have not moved in a year. That is where to put the effort, and it is a storage question rather than a cleaning one.

Widows go in the same short list of places every time — under pot rims, in meter boxes, under outdoor furniture — which is set out in are there black widows where you live.

The autumn surge, again

If the question arrived in September because the house suddenly seems full of spiders, the answer is neither dirt nor invasion.

Mature males leave their webs and walk in late summer looking for females. They have been in the building all year. What changed is that they are now adult, large and moving in the open — why there are suddenly spiders everywhere in autumn.

Nothing about the house changed, and sealing it would not have prevented it.

Whether to want them gone

A house with spiders has fewer flies, moths, mosquitoes and silverfish, because something is eating them. Removing the spiders does not remove the insects, and the insects were the reason the spiders were there.

There is also no achievable end state. Wall voids, lofts and crawlspaces hold a population that indoor cleaning never touches, and the outdoor supply is continuous.

The reasonable target is fewer in the rooms you use, which is achieved by the outdoor lighting, the gaps and the web removal — and by moving the individual ones out when they appear, which can be done without killing them in about thirty seconds.

What not to bother with

• Conkers, tested and ineffective.
• Peppermint and essential oil sprays, marketed heavily, evidence thin.
• Ultrasonic devices, which do nothing.
• Perimeter insecticide spraying, which reaches surfaces spiders mostly do not walk on, kills the predatory insects along with the rest, and does not touch the population in the voids.