Why are there so many spiders in my house in September?

The Burke Museum's arachnology department has been correcting this one for years. House spiders have lived indoors since at least the Roman Empire and spread through egg sacs on furniture and building materials; they spend their whole lives inside. Outdoor spiders are cold-blooded, aren't attracted to warmth, and go dormant in winter with their own natural antifreeze (Burke Museum). The late-summer surge is males on the move. The females and juveniles stay hidden, which is why you suddenly see spiders in the tub and on the walls and then don't.

Spraying visible spiders in September kills a few males and changes nothing. A house with a steady spider population has a steady insect population feeding it, so the real levers are reducing the bugs they eat, sealing the gaps insects use to get in, cutting down clutter and cardboard in the basement and garage, and running a dehumidifier where it's damp. Sticky traps along baseboards tell you where the traffic is. Long Island has no medically significant spiders living in houses; the common ones are harmless.

Basements, garages, crawl spaces, and the wooded-lot homes of the North Shore carry the most spider traffic, and the September spike lands right when stink bugs, lady beetles, and cluster flies are also showing up. A general insect treatment of the perimeter and the basement in early fall handles the insects that feed them, which is the only spider control that lasts.