Every time I have seen a spider at home, in the bathroom, whether it was in a house or in apartments, whether on the bottom or upper floor, I always immediately assumed that it had come "through the pipes"; that is, crawled up through the drain pipe leading into the bathtub, or the drain hole in the floor which takes care of any water that spills out on the floor.

Or even that it had swimmed all the way up through the water toilet.

Luckily, it hasn't happened for quite some time now (knock on wood...), but this thought was especially present in my mind when the spider was sighted in the actual bathtub.

My question is: do spiders actually crawl up such pipes, into homes? Or is this a false assumption? Don't spiders tend to come in from opened doors and windows? Not through pipes?

I mean, it's not like the drain pipes lead directly down underground with dirt and creatures living there. It's still connected to the bigger sewage pipes, no? I cannot imagine any creature surviving not only the oxygen-less, long trip through these large sewage/water pipes, but to also have the strength to stop and actively push themselves up and keep crawling all the way up to my apartment/house's bathroom.

But maybe I underestimate those vile creatures of pure evil.

On the other hand, it seems unlikely that a spider would come from the outside, though a window or door, only to find itself crawling into the bathttub and be sighted there, so that talks against my theory that it's impossible for insects to enter through these drain pipes...

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    $\begingroup$ you see spiders in the bathtub more than other places because once there they often can't escape, and when there, they are always found. $\endgroup$ Apr 13 '20 at 8:07
  • $\begingroup$ The drain pipes in houses are not full of water. $\endgroup$ Apr 13 '20 at 10:32
  • $\begingroup$ @morbo but the u-bends on sinks, baths, showers and toilets do provide water traps that are full of water... $\endgroup$
    – Solar Mike
    Apr 13 '20 at 12:25
  • $\begingroup$ @SolarMike pretty sure you know both of us know that, and the OP has the misconception that the pipes are full. $\endgroup$ Apr 13 '20 at 12:26

No, they come in through all the gaps and cracks in the building frame. They also come when you have a window open for ventilation or through ventilation grills.

They are not swimming against the sewage and coming up through the plug hole.

  • $\begingroup$ The gap under external doors is another point of entry. $\endgroup$
    – Fred
    Apr 13 '20 at 12:16

The concept of a spider navigating a gravity driven sewer system is not realistic. The water flows downhill and the spider that could swim against the water current would be all legs (and our overloard). Water surface tension would mean any spider would have difficulty getting out of the water.

All plumbing systems have a vent stack through the roof so they could get in to the plumbing system, but they cannot get past water traps in the plumbing system meant to keep sewer gas out of homes.

Dryer vents or bathroom exhaust fans would be more realistic entry points.

Odds are most spiders are coming in on a person's clothes or something brought into the home. Laundry drying on clothes lines is a common entry point (for me - catch and release).

They end up in tubs because they cannot get out of them due to slippery vertical slopes. A healthy spider would not fall into a tub, but without a source of food...


Unlikely but possible, they easily enter under doors and other places. However , I had a scorpion enter once through the sewer. A state Parks and Wildlife guy told me the drop down the stacks ( sewer vents) on the roof. No swimming needed, air all the way to the bathtub and sink vents.I put screens over all my stacks.


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