If you walk into your bathroom and spot small, brown worms swimming around in your toilet, then your bowl is likely housing either horsehair worms or drain fly larvae. Although neither of those moisture-loving worms bites or spreads diseases to humans or pets, their presence can still be quite startling. Identifying the worm and following the proper sanitation and exclusion methods can get rid of the unsightly wigglers and help prevent future worm problems.
About Horsehair Worms
Although just one horsehair worm (Gordius spp.) can show up in your toilet bowl, they frequently appear in masses of more than 100 worms, forming a twisted, knotted ball that looks like a Gordian knot, hence the nickname "Gordian worms." Adults have pale to deep brown bodies that reach 4 to 14 inches long, but only about 1/25 inch around, or about the width of dental floss. (ref 2, ref 5, ref 1)
Adult females lay as many as several million eggs in 12- to 24-inch strings in water. The larvae hatch two to four weeks later and search for a suitable insect host to parasitize. Common hosts include crickets, grasshoppers and beetles, but dragonflies, millipedes, centipedes and cockroaches can serve as hosts as well. The host feels compelled to find water about 90 days after ingesting a young worm. Once it does, the mature horsehair worm emerges and swims off.
About Drain Flies
Adult drain flies (Psychoda spp.), sometimes called moth flies, only reach about 1/6- to 1/5-inch long and have dark, overly large wings that make them look like tiny moths. The flies feed on the organic matter and bacteria that cause slime to develop in drains and pipes, and breed in shallow, contaminated water sources.
Adult females lay clusters of 10 to 200 eggs in moist organic matter, such as that found inside toilet tanks or beneath the toilet bowl rims. The legless, gray larvae emerge in less than 48 hours The worms only reach about 1/2 inch in length, feeding on the organic matter for nine to 15 days before pupating into adulthood.
Controlling Toilet Worms
Horsehair worms are considered beneficial since they parasitize insect pests, so no chemical control is needed. However, if you can't handle the sight of worms swimming around in your toilet bowl, simply scoop the wigglers out of the water and throw them in the trash.
Controlling drain fly populations requires removing the gelatinous buildup inside of drains and pipes. Carefully pour a pot of boiling water down drains to help loosen the slime. Follow up with a commercial drain cleaner, following the instructions and safety precautions exactly.
Deter adult flies looking for a food source or breeding ground by thoroughly cleaning your toilet using a disinfecting toilet bowl cleaner and a long-handled scrub brush. Take special care to completely remove any slime or gunk that developed under the rim of the bowl. Examine the inside of the toilet tank, using a scrub brush and disinfecting cleaner to remove any film or slime that you find.
Preventing Future Infestations
Horsehair worms that appear in your toilet are likely from infested insects seeking water or from one you stepped on and tossed into the bowl. Throw dead host insects away in an outdoor garbage can. Prevent both insect hosts and drain fly adults from entering your home by caulking or covering any potential entry points, including around windows, doors, vents and air conditioners.
Drain flies often appear in toilets that don't receive much use, so flushing infrequently used toilets every few days can keep water moving through the bowl and pipes, which keeps the pests from moving in.