Drain Fly Larvae In Toilet

Have you ever noticed a black or white film on the surface of your toilet bowl? Chances are you have encountered drain fly larvae. These insects are known as drain flies, moth flies, or sink flies, and unfortunately, they can end up in places where you don’t want them.

Drain fly larvae in toilets is a common problem, especially during spring and summer. They are pests that can damage your health and property. The larvae prefer areas of human waste such as toilets and drains, which are dark, warm, and provide a sufficient supply of food for them to breed. It’s crucial to catch the source of an infestation early and eliminate it. We also recommend regular checks of your plumbing system by a professional plumber.

The insect infestation is often hidden deep in your system. In this article, we discuss how they come to invade your home and, importantly, how you can get rid of these larvae so that they never come back.

What Are Drain Fly Larvae?

Drain fly larvae are the immature stage of drain flies. They are a similar size to gnats and fruit flies -1/4 inch to 1/2 inch long- and are identified by their tiny, moth-like wings and round, fuzzy bodies.

These little creatures tend to hop rather than fly. They have a lifespan of eight to twenty-four days, and the female can lay around three hundred eggs in forty-eight hours.

What Causes Drain Fly Larvae in Your Toilet?

The plumbing system is the most common way they find their way into your home. Clogged or overflowing toilets that don’t flush properly cause excess waste to accumulate in the tank, which can grow mold and become an ideal breeding ground for these pests. Which makes toilets, drains, sewers, and septic tanks a perfect breeding ground. Hence their common name “drain fly.”

They are also attracted to areas that contain nutrient-rich organic matter. Moth fly larvae can survive on decaying matter, organic debris, standing water, and food waste.

How Do I Check If I Have Drain Fly Larvae?

Use the following checklist to determine whether you’re dealing with an infestation.

  • Flies lay their eggs in clogged sinks, tubs, and toilets. Check the toilet bowl regularly (every week or two) after use; if there are traces of human waste or tissue paper, drain fly larvae could also be present. If you suspect a drain fly infestation, using a torch, inspect your drains by looking for larvae or adult flies.
  • Drain flies lay their eggs in garbage disposals and drains where there is rotting food or other organic material. When they hatch, they go through a series of stages as they mature. The final stage of their life cycle is when they become adults and mate before dying off within a few days after hatching from the larvae. These eggs produce the odor you smell as they grow into adults within your plumbing system.
  • Check around the rim of your toilet bowl. That’s where the flies lay their eggs. If you find any eggs, remove them immediately with a cloth or wire brush and flush them — they can cause problems if they hatch and start growing inside the toilet.
  • If you are unsure whether you have a drain fly infestation with a flashlight, check the sides of your outside drains for thin, tube-like larvae. If you don’t find any here but are sure there is an infestation, this could mean that the eggs have been laid deeper within your pipes.

Can Drain Flies Live In Toilets?

Yes, they can! They are not just living there but breeding.

They feed on the fluids exuded by hair, skin, and other organic material. The uric acid smell, the byproduct of urine, is also an attraction to these moth flies. It can pool in your toilet bowl and attract them to hibernate. The toilet itself is not a perfect environment for these insects to breed.

They are also attracted to light and often come out at night or when you turn on the bathroom light. They might seem harmless, but they threaten the health of you and your family. If you see any bugs in your toilet or sink, ensure you get rid of them immediately by flushing them.

How To Get Rid Of Drain Fly Larvae

  • A homemade cleaning solution of baking soda, salt, and vinegar is a great way to clean all your outside and indoor drains. This natural cleaning mix will remove buildup in your pipes and kill the fly larvae in them.

Combine one part baking soda, one part salt, and two parts vinegar, and then just before heading off to bed, pour the solution down your drain. Let the mixture foam up overnight. In the morning, flush boiling water into your drain to clear away any foam and wash away any buildup.

  • You could also pour a recently boiled kettle of water down your drain one to two times daily for a week. This method is more effective for killing larvae inside the pipes than dealing with adults that can fly. Repeating the process will ensure these pests won’t return if the first pour didn’t remove all the organic material.
  • To clean PVC pipes, use pipe brushes and cleaners designed for kitchen and bathroom drains.

Cleaning these pipes manually and removing the sludge inside them eliminates the drain flies’ food source and prevents them from laying more eggs.

Let your hot water run down the PVC pipe, then insert your vent or snake brush as far up or down the pipe as possible to dislodge eggs, larvae, and buildup. If you’re cleaning your sink’s pipe, remove the U-trap under the sink and clean out any additional buildup.

  • Wherever you see a mass of adult drain flies, you can make a vinegar trap to dispose of them. After pouring some apple cider vinegar into a jar covered in a plastic wrap. Pierce a few holes into the wrap using a needle or scissor tip; the flies will be attracted into the trap through those holes but cannot escape.

To make the flytrap even more effective, add some ripened fruit to the vinegar. Add a small amount of dish soap to the mixture to make it more difficult for the flies to escape.

  • Enzyme cleaners are the best way to deep clean your drain. Run some warm water down the drain, stick a metal pipe brush as deep into it as it will go, and remove it to dislodge any buildup. Then, pour in your enzyme cleaner and let it sit for several hours (check the instructions on the bottle for details). Effective enzymes will break down any organic residue, preventing it from causing clogs in the future.

Flush out the residues by running some more water through the drain. Enzyme drain cleaners are non-toxic, environmentally friendly, and safe for kitchens. Once cleared of buildup and larvae, flies will stop appearing.

Enzyme cleaners such as Drain Fly Trap or Bio-Clean Professional Drain Cleaner are also available, specifically created to eliminate these pests.

  • If you need to catch a few drain flies, try putting duct tape over your drain (sticky side down) overnight to trap and kill the adult insects. 
  • Finally, ensure that you throw out your food waste in covered bins, with a mesh covering the opening to keep pests out.

Frequently Asked Questions

Are Drain Fly Larvae Harmful?

They do not bite or transmit disease to humans, but they can cause asthma in some people, and the larvae can lead to myiasis, an infection in which the larvae actually grow inside human tissue like muscle or skin.

Can Drain Fly Larvae Be a Sign of an Underlying Plumbing Issue?

If you have a drain fly infestation, it’s important to know that they are not a sign of an underlying plumbing issue. In fact, the presence of the larvae itself is often the problem.


The most significant indicator of an infestation is adult drain flies. If you see any drain flies around your home, there is likely to be a pool of standing water, moist decaying organic waste, or food leftovers nearby, encouraging them to breed and eat.

However, ultimately, the ideal solution is prevention.

We recommend regular checks and maintenance of your toilets, drains, sewers, and septic tank. Ideally, you would call a professional plumber to check your plumbing system, including any PVC or metal piping.

Place all food waste in covered waste bins, perhaps even with a wired mesh to seal the opening. Habitual house cleaning of the bathroom, toilet, and kitchen areas with sanitary products would limit the occurrence of these pests.

As discussed, there are many ways to eliminate drain flies and their larvae. The best way depends on what works for you. Try one method at a time and then move on to the next if you don’t see results.

With the help of the advice and tips in this article, hopefully, you’ll get rid of or prevent drain fly larvae once and for all.

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