Discover the Complete Life Cycle of Drain Flies

Drain fly gnat on white floor.
Cherdchai Chaivimol/

Written by Crystal

Published: February 17, 2023

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Drain flies get their name because they hang out around sinks and drains. Sometimes called sink flies or moth flies, these insects have tiny hairy bodies that are usually less than 5 mm long. Females can lay as many as 100 eggs at a time, and within 48 hours, they’ll begin their fast and strange journey to adulthood.

What is it like to be a drain fly? Let’s find out. Follow along as we explore the complete life cycle of drain flies.

Drain Fly Lifecycle

The drain fly’s life cycle breaks into four main categories: egg, larval, pupal, and adult. A normal life cycle takes 21 to 27 days to complete. However, warm temperatures can accelerate the drain fly’s life cycle. Let’s start by exploring the egg stage.

Stage One: Egg

The first stage of the drain fly’s life cycle is the egg stage. This is when the female deposits a large egg mass into wet soil or the sides of drains.

Wherever the eggs are deposited, there has to be moisture. Without moisture, the eggs won’t survive. Sometimes egg masses can contain as many as 100 at a time. However, females are more likely to produce 15 to 40 eggs with each mass.

Drain fly eggs are less than 1 mm in size. These small eggs are also completely transparent. Once temperatures reach 70° F, the eggs will hatch. Typically, the egg masses hatch in less than two days.

Stage Two: Larvae

If you’ve seen mosquito larvae, you’ll have a good idea of what drian fly larvae look like. These small drain flies are slender and have a creamy brown color. Even in the larval stage, there’s a distinct head with developed mouthparts.

In total, drain fly larvae have 11 segments in their body. The last two segments have breathing siphons. The breathing siphons are kept safe by four tracheal papillae, a type of fleshy appendage.

The larval stage is the longest part of the drain fly’s life cycle. When temperatures are right, the larval stage can last as many as 15 days. If it’s too warm, the larva stage lasts only eight days.

Ideal temperatures for larvae drain flies are right around 70° F. Once it starts to get closer to 85° F, it’s hard for the drain flies to thrive.

What do these larval drain flies do all day? The larva usually hangs out in the topsoil. They stay toward the top of the soil so that they can breathe. They also find organic material to feed on. Waterlog soil is known for being full of drain fly larvae. They can also dive deep into sewage filter beds or trapped air bubbles.

Stage Three: Pupae

The pupal stage is a shorter part of the drain fly’s life cycle. Pupay only needs 24 to 48 hours before transitioning into the adult stage. A drain fly pupa is easily identified by its yellow-brown color and trumpet-like horns. The small horns come out of the top of their head.

Stage Four: Adult

Drain fly gnat on white floor.

Adult drain flies have fuzzy brown heads and wings. On average, females are bigger than males.

Finally, the drain fly will arrive at the final stage. Males transition into the adult stage before females. However, they only live for a few days. Females who haven’t laid eggs can live as long as seven days.

Adult drain flies have fuzzy brown heads and wings. On average, females are bigger than males. While males are usually 3 mm long, females have an average length of 4.5 mm.

Typically, drain flies begin emerging as adults at the beginning of spring. Peak populations happen in late summer. However, fluctuating temperatures can change when the adult populations peak.

Do Drain Flies Come from Drains?

Drain flies come from the outdoors. They enter drains through small holes when they smell organic matter. These flies are most active when they gather around sink drains during the evening, a behavior similar to that of fruit flies.

If you see drain flies in your house, you must eliminate any standing water. Run the water in your sinks and flush all of the toilets. This will help get rid of any drain fly habitats.

If that doesn’t work, it’s time to call a pest control specialist. Drain flies have hairy legs that can help them avoid being washed away with water. Sometimes special chemicals are necessary to eradicate an infestation.

Final Thoughts on the Life Cycle of Drain Flies

There you have it, the complete life cycle of drain flies. To recap, a normal lifespan moves through four stages and lasts about 25 days, with females outliving males. Finally, warm temperatures play a big role in how these flies develop. The warmer the temperatures, the shorter the life cycle.

You can learn more fun fly facts with the articles below.

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About the Author

Crystal is a dedicated writer at A-Z Animals, focusing on topics related to mammals, insects, and travel. With over a decade of experience in the world of research and writing, she also fulfills the role of a skilled video and audio engineer. Residing in sunny Florida, alligators are Crystal's favorite animal.

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