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Four groups of insects and other arthropods are commonly found in bathrooms. Here’s why they’re there.

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Editor’s Note: This article was reprinted with permission from Techletter, a biweekly training letter for professional pest control technicians from Pinto & Associates. To subscribe, visit

Do you have customers who always seem to have an assortment of pests in their bathrooms? There are basically four groups of insects and other arthropods that are found in bath-rooms. They include:

  1. Moisture Lovers. Most insects need moisture to survive and, generally, the more humid their environment, the better they like it. German cockroaches prefer a humidity of 90 to 95 percent. Other high-humidity pests found in bath-rooms include silverfish, springtails, psocids and fungus beetles. Occasional invaders will often end up in a bathroom, especially if it is on the ground level.
  2. Those Attracted to Lights. Bathrooms often have bright lights above the sink and night-lights on when no other lights are on elsewhere in the house. Flying insects attracted to lights will find their way to the lighted bathroom while residents sleep. In the morning, mosquitoes, moths, midges and others will be waiting.
  3. “Resident” Bathroom Pests. Drain (moth) flies can live and breed in bathrooms. The larvae feed and develop in the scum down inside sink, shower and tub drains. Emerging adult flies may remain in the bathroom, lazily circling around or sitting on walls and then laying eggs once again in the drains.
  4. Predators. Predatory insects and other arthropods end up in bathrooms because their prey are attracted by all the reasons listed previously. Predators such as spiders and house centipedes are always looking for an insect meal, and the bathroom is a good place to find one. When insects end up in a bathroom, predators will find their way there, too. These predators don’t mind the extra moisture found in a bathroom either.

Insects are probably more likely to end up in bathrooms with windows, especially if the bathroom is lit at night. Advise customers to check bathroom windows, and maybe doors, for gaps that let pests in. Bathroom windows should be closed and covered with curtains at night to block light. Night-lights should use a motion sensor or have the light dimmed or shielded. Keep bathroom doors closed at night, if possible, to avoid drawing insects from elsewhere in the house. If bathrooms remain too damp, residents should consider installing a dehumidifier or additional ventilation. If drain flies are the problem, scrub and treat drains with a bacterial or enzyme cleaner.

The authors are well-known industry consultants and co-owners of Pinto & Associates.