How to get rid of sewer drain flies?

You’ve likely never heard the term “Psychodidae,” but you’re probably familiar the pest that’s been assigned this scientific moniker. Most homeowners know these pesky insects as drain flies, sewer flies, moth flies, sewer gnats or sink flies. They’re short and furry, giving them a moth-like appearance, and while they’re native to humid climates, it’s not uncommon to find them in plumbing drains and sewage systems throughout Chicagoland.

And while these pests are mostly harmless (some asthma sufferers have reported flare ups due to contact with them), they’re definitely annoying and almost always an unwelcomed guest in the home. So, what causes sewer flies, and more importantly, how do you kill drain flies?

Identifying drain flies

There are millions of species of insects out there today, so it can be confusing trying to find out which one is bothering you. For example, fruit flies are perhaps the most common pest you’ll find in your kitchen, but they’re more attracted to your fruit out in the open and your trash than your drains. There’s also the fungus gnat, which has similarities to drain flies, but are more likely to be found in your potted plants.

The drain fly is light gray or tan and has a dark border around its wings. It’s only an eighth of an inch long, but it has distinctive moth-like antennae that are fuzzy. Their bodies are fuzzy as well.

Where to find them

Drain flies lay their eggs in your drains where sludge/organic material accumulates. The larva will feed on the material, grow there, and once matured, the adults will crawl out of your drain(s) and fly to a nearby wall or ceiling. Sewer flies in the basement, sewer flies in the bathroom, sewer flies in the toilet – it doesn’t matter which room or what drain – given the proper environment, they’ll breed and thrive.

Females lay between 30 and 100 eggs in drain water, and the eggs hatch within 48 hours. The pupal stage for the fly lasts around 20 to 40 hours. They don’t feed in this stage, but remain submerged in water close to the surface. Adults are only half the length of the larvae, but they are broader. Adults live for about 20 days, which is plenty long enough to get on the nerves of homeowners whose drains are infested with them. Now, deciding on a sewer flies treatment strategy is in order.

Best way to get rid of sewer gnats

When you’ve determined that you indeed have a drain fly problem, you need to take the right course of action to get rid of drain flies. Some homeowners prefer using an enzyme that is poured into the drain. It eats away at the organic matter that brought you your drain fly problem in the first place. The enzyme essentially removes the food source, but they generally take several hours to work. The bonus is that once you’ve removed the organic material, you’ve also prevented future clogs from occurring and future drain flies from proliferating.

If you’ve got several drains throughout your home as most homeowners do, routine maintenance will help you from experiencing reoccurring problems. If you’ve got drains where hot water isn’t usually run, you’re going to see more drain fly action, which means regularly treating the drain with cleaner followed by a hot water flush should help alleviate the problem.

How to kill them, fast

To get rid of drain flies fast, slowly pour boiling water into your drain. Be careful because boiling water can have adverse effects on plastic pipe material. The hot water is fairly efficient at wiping out larvae and eggs, but entomologists (scientists that study insects) have reported that this is likely just a temporary fix and that the flies will multiply again in short order.

Another quick fix is to pour drain cleaner down the affected pipes. This will remove the clogs and slime where drain flies lay their eggs. However, drain cleaner isn’t cheap, and if the first treatment doesn’t wipe them out, you have to reapply the cleaner until it does.

How to get rid of drain flies naturally

If you’re focused on finding a green, more organic method or natural way to get rid of drain flies, consider a natural remedy, which is the old-school swatting method. While this will rid you of the adult flies, you still have to get at the root of the problem – the eggs and larvae.

To do this, use a metal pipe brush and clear away the accumulated, hidden debris in your pipes. The brush will scour away the slime, grim and debris in which the eggs are laid. Just move the brush up and down and run hot water to flush out the matter. You can also use a plumbing snake to get deeper into your pipe system. Also, for those looking into how to get rid of drain flies naturally, try using a vinegar and baking soda solution for a thorough drain flies removal method.

How to prevent drain flies from returning

A drain fly-free home is one where the pipes are completely clean. While cleaners and hot water can do an “okay” job at eliminating sewer flies, these insects are covered by water-repellent hairs and can’t be drowned. Furthermore, the eggs are resistant to chemicals and thermal assaults.

What kills drain flies? Sure, drain fly killer chemicals can be part of the solution, but the best pest control method is a thorough cleaning of your drainage system, which is often only possible through the services offered by a professional plumbing contractor. In many cases, their drain fly treatment involves a complete and thoroughly deep cleaning of the pipes in the sewer system.

Eliminate sewer and drain flies with our drain treatment services

The best way to get rid of drain flies and to keep them away is to call in a plumber. Valley Fire Protection, we’ve got the tools necessary to eliminate sewer flies. For example, our jet rodding services completely remove all organic materials from your pipes, even deep within the plumbing system. This not only removes everything that a drain fly needs to proliferate, it also keeps your plumbing clog-resistant for the foreseeable future.

Contact us today and let’s schedule a thorough cleaning of your pipes and drains. If these pesky flies are showing up at home, please contact our residential plumbing division.

Related Topics: Plumbing Problems // Sewer Flies
By: Tom Hartel
I acquired my expertise by directing day-to-day operations of the business for over 20 years. Continuous hard work helped me become a nationally recognized speaker and expert on fire protection, fire sprinklers, special hazards, and plumbing systems. In this blog, I share my knowledge that will hopefully help you make better decisions for your projects.


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