If you're washing the dishes and you start noticing fuzzy flies about the width of a shoestring shooting of your kitchen sink like fireworks on the Fourth of July, you might have a drain fly problem. And as their name implies, drain flies do live in drains.
Like most flies, drain flies are around 1/16–3/16 inches (1.5-5 millimeters) long with six legs, a pair of wings and antennae. Their bodies are light gray or tan. Their distinguishing characteristic is the hair that covers their body, antennae and wings, giving them a fuzzy — some could even argue adorable — quality. That's also why they are sometimes called moth flies because they resemble the fuzzy appearance of moths.
Frank Meek, technical manager with Orkin and a board-certified entomologist, notes they are also called sewage flies or filter flies. "These names stem from places or situations that represent typical breeding and development sites for the pest," he explains via email.
Moist locations — preferably covered with their favorite entrees like food scraps, sewage, decomposing plant life and other nutrient-dense organics — are hot spots for these flies. That makes your sinks, storm drains, shower drains, septic tanks, compost piles, as well as any pile of dog feces in the backyard, seem like a gourmet buffet.
Like all insects, drain flies don't stick around to nurture their young. They are happy to leave their eggs in the same places they eat: food waste, feces, logs and in your sink. But their favorite spot in and around your home is usually soil.
"Moist soil is their favorite breeding ground, either in premixed soil, a pre-potted houseplant, or underneath your home. Since this activity occurs out of sight, homeowners often don't notice a problem until fully grown drain flies appear in kitchens and bathrooms," Meek says.
Once the eggs hatch into tiny white larvae, it takes about 8-24 days to fully mature. As adults, their life span is a measly two weeks, compared to a housefly that lives up to a month.
What to Do if You Have Drain Flies
Meek points out that you're most likely to see them resting on walls because flying isn't their strong suit. "Drain flies are weak fliers, so indoors, they are usually seen crawling on walls or other surfaces," he says. If you suspect you have drain flies, try keeping a close eye on your kitchen after dinner. "Their greatest activity is in the evening when they may fly or hover above drain opening indoors or sewage filter beds, outside."
The good news is that if you have drain flies, it doesn't mean you're living in filth. It most likely means you have a slow, clogged drain.
"Drain flies gather, mate, and lay eggs in moisture or standing water. The slimy film that forms in sewers and drains is a favorite breeding spot and food source. Putting off regular cleaning and maintenance of these areas may attract the pests and offer them a place to feed and develop," Meek explains.
Despite rare cases where inhalation of drain fly body parts causes bronchial asthma, these pests aren't known to spread any serious diseases to humans or large animals, Meek says. However, it's no reason to put off removing them. Drain flies can land on your charcuterie board and spread bacteria; that's a bit much even for a blue cheese fan.
How to Remove and Prevent Drain Flies
If you notice these fuzzy flies sprouting out of your drain while washing your dishes, it's time to clean house. Here's what to do:
- Look for the breeding site. "A thorough inspection is required to find the fly's breeding site, so you should look at a variety of places – drains, dirty garbage cans, saucers under potted plants, birdbaths or feeders, clogged roof gutters, clogged storm drains, air conditioners, cooling towers, moist compost and rain barrels," Meek says. Check also around your sewer or septic tank if you have one. "Once organic material is removed (along with the larvae), the problem is solved, except for the adult flies. They will live about 20 days but will have no place to lay eggs to continue their life cycles," he adds.
- Clean your drains. But your typical drain cleaner won't fix the problem, according to Meek. "Foaming enzymes applied by pest control professionals break down the film coating that drain flies are eating and may also target drain fly eggs, thus helping to prevent future breeding. This treatment is not dangerous and does not harm plumbing," he says. Another tactic is to use an ultra-low volume (ULV) fogging machine to kill the flies, but this doesn't address the issue of the breeding site(s) and so doesn't provide long-term control.
- Resist the urge to pour bleach down your drain. "While this chemical might get rid of some larvae, bleach passes quickly down the drain and does not penetrate the thick buildup where eggs are deposited by the female drain fly. As a result, in most cases, bleach does not get rid of drain flies," says Meek. It's also corrosive and can damage old pipes, he notes. And whatever you do, don't mix bleach and ammonia down the drain. This can create chlorine gas, which can be fatal if inhaled.
Natural Solutions to Get Rid of Drain Flies
Here are some ways to remove and prevent drain flies that don't involve chemicals, courtesy of This Old House:
- Pour boiling water down your drain two times a week to remove buildup.
- Leave a baking soda, salt and vinegar solution in your drain overnight. Then, pour boiling water down the drain the next day.
- Try a vinegar, soap, sugar and water combo left out in bowl on the kitchen counter. The flies will be attracted to the sweet, sugary temptation (aren't we all?) and drown in the sticky soap.
- If all you've got is apple cider vinegar, that could work, too. Pour it into a container and tightly cover it with plastic wrap. Puncture a few small holes into the plastic so that flies can get into the container, but not out.
You'll still need to find the breeding site and deal with that so as not to have a recurrence of drain flies.