Why Do Insects Crawl Up the Bathtub Drain?

Insects that travel indoors and take up residence in a home are a common problem of homeowners. Insects appear frightening and offensive to some people, they can transmit disease and bacteria, and some can even present safety risks to the human residents of a home. At one point or another, you are likely to find insects in the bathroom, and understanding why they go there in the first place can be a critical part of effectively controlling and removing them.

Bathrooms and Insects

According to Iowa State University entomologist Donald Lewis, a common misconception of many homeowners is that insects are more common in the bathroom than in other rooms because insects live in the sewer and crawl up sink drains, toilets and shower drains. This is unlikely, because filters on plumbing are far too fine for insects to crawl through. Additionally, most insects that might travel indoors would not be able to survive for very long in water-filled sewer systems. An insect observed in the bathroom, then, even if it is staying near the bathtub drain, probably did not crawl up through the bathtub drain.

Common Bathroom Insects

However, there are insects that are more likely to be found in the bathroom than in other rooms, whether they made their way into the bathroom via the tub drain or any other route. Many insects prefer the moisture and shelter that residential bathrooms provide; in fact some insects, such as cockroaches and silverfish, will seek out the most moisture-rich rooms in the house. Insects that travel into the bathroom in turn attract other insects that prey on them as a food source.


So, if insects crawl up tub drains only very rarely, the question remains of how they get into the bathroom if not through the drain. Insects make their way indoors through cracks and holes that serve as entrances from outdoors. Insects do not travel inside unless they have a good reason -- namely a food source, shelter, a source of water or better yet, all three.

Control Methods

Knowing what draws insects indoors in the first place can go a long way in designing an effective insect control program. Cleaning dark, secluded areas that humans do not frequent can eliminate sources or shelter for the insects. Sealing any cracks or openings that serve as an entryway indoors for insects is also effective. If insect problems become a serious nuisance in the bathroom, and regular cleaning does not alleviate the problem, treat with approved insecticides, or lay a few insecticidal bait traps in the bathroom.

Eoghan McCloskey

Eoghan McCloskey is a technical support representative and part-time musician who holds Bachelor of Arts degrees in English and political science from Texas State University. While at Texas State, McCloskey worked as a writing tutor at the Texas State Writing Center, proofreading and editing everything from freshman book reports to graduate theses.