Why Do Some Houses Have So Many Spiders?

Spiders Follow Prey

A spider population is a function of the insect population. Nothing else comes close as an explanation. If a building has lots of spiders, it is because the building has lots of flying and crawling insects, and the spiders are simply the visible end of that.

Which means the useful question is not "why do I have spiders" but "what is attracting the insects".

Outside Lighting Is the Biggest Single Factor

A white security light or a porch light left on overnight pulls flying insects to the wall from a surprising distance, and the spiders set up where the food arrives. Doorways, porches and the wall under a light are where you see the result.

Moving the light away from the door, switching to a warmer-toned bulb, or putting it on a sensor rather than a dusk-to-dawn timer makes a genuine difference within weeks. It is free, and it does more than most treatments.

Harbourage: Somewhere to Sit Still

Spiders need somewhere undisturbed with structure to anchor a web. Clutter stacked against garage walls, boxes under a bed, a cellar full of stored things, ivy on an external wall, log piles by the door, and the corners of a conservatory roof are all ideal.

A cluttered garage with a light by the door is close to a purpose-built spider habitat, which is why garages generate more of our spider calls than living rooms do.

Ways In

Gaps under doors, unsealed vents and airbricks, gaps around loose-fitting window frames, and trickle vents left open. None of those can be sealed completely and no honest company will claim otherwise, but a brush strip on a door genuinely reduces the traffic.

The Season That Is Not About Any of This

Late summer and early autumn, large house spiders appear indoors for two or three weeks. Those are males wandering to find a mate. They are not living in your house, they are not a sign of an infestation, and they stop on their own.

If that is what you are seeing, no treatment is worth buying. We will say so.