Moth Flies Identification Guide
Psychodidae (Family)
Moth flies are small, fuzzy, moth-like insects that breed in the organic buildup inside drains and other moist areas. Also known as drain flies or sewer gnats, they are a common nuisance pest in bathrooms and kitchens.
Taxonomy
Moth Flies Coloration
Common color patterns to help identify moth flies
Moth Flies
Seasonal Activity
When moth flies are most active throughout the year
Where Moth Flies Are Found
Hover over states to see their names. Green regions indicate where moth flies have been reported.
Moth Fly Identification Guide
Physical Characteristics
Moth flies are small insects, about 2 to 5 millimeters long. Their most noticeable feature is their fuzzy, moth-like look. Both body and wings are covered with tiny hairs. This gives them a furry texture that sets them apart from other small flies.
When resting, moth flies hold their leaf-shaped wings like a roof over their bodies. The wing veins run parallel from base to tip. This pattern is unique to the Psychodidae family. Their color ranges from pale gray to tan or brown. Some species have small white spots on their wings.
These flies have long antennae covered with fine hairs. Their large eyes stand out on their small bodies. Despite having wings, moth flies are weak fliers. They make short, hopping flights and prefer to walk or run across surfaces.
Common Species in North America
The most common species in homes is Clogmia albipunctata, also called the bathroom moth fly or filter fly. This species is found across North America. It thrives in warm, humid bathrooms and kitchens.
Another common species is Psychoda alternata, which has similar habits. The Psychodidae family includes over 2,600 species worldwide. Only a few are common household pests. About 112 species live in the United States.
The Psychodidae family also includes sand flies, which bite and live mainly in tropical areas. However, the moth flies found in North American homes do not bite. They are simply a nuisance.
Moth Fly Behavior and Biology
Life Cycle
Moth flies go through four life stages: egg, larva, pupa, and adult. In warm conditions (68 to 86 degrees Fahrenheit), the full life cycle takes just 8 to 24 days.
Females lay 30 to 100 eggs in the slimy film inside drains. They place eggs just above the water line in moist organic matter. In warm conditions, eggs hatch within 32 to 48 hours.
The larvae are legless and see-through. They have a dark breathing tube at their rear end. They use this to get oxygen from the surface since they cannot breathe underwater. Larvae grow through four stages over 9 to 15 days. They feed on bacteria, fungi, and organic matter in drain slime.
The pupal stage is short, lasting only 20 to 40 hours. Adults can breed within hours of emerging. Adult moth flies live about two to three weeks. Females may lay several batches of eggs during this time.
Habitat Preferences
Moth flies live in moist areas with decaying organic matter. The larvae need a film of organic material to grow. This makes drains their most common breeding site in homes.
Adults are most active at night but may come out during the day in shaded areas. They are drawn to light and may gather near windows or light fixtures. During the day, they rest on walls and ceilings near their breeding sites.
Moth flies stay close to where they hatch. If you see them in your home, the breeding source is likely just a few feet away. This makes finding and treating the source easier than with other pests.
Breeding Sites
Moth flies can breed anywhere with moisture and organic matter. Common breeding sites in homes include:
- Bathroom sink, shower, and bathtub drains
- Kitchen sink drains and garbage disposal units
- Floor drains in basements, laundry rooms, and garages
- Condensate drains from air conditioning units and refrigerators
- Sump pump pits and basins
- Septic tank vents and damaged sewer lines
- Infrequently used drains where water has evaporated
- Areas with hidden leaks or water damage behind walls
In commercial settings, moth flies often breed in floor drains, grease traps, mop drying areas, and condensation pans beneath refrigeration equipment.
Treatment Methods for Moth Flies
Effective moth fly control focuses on eliminating breeding sites, not just killing adult flies. The larvae develop in organic biofilm, so treatments must remove this material to achieve lasting control.
Source Identification
Before treatment, find all breeding sites. The tape test works well: place clear tape over drains overnight, sticky side down, with small gaps for air. If moth flies breed in that drain, you will find adults stuck to the tape in the morning.
Test multiple drains over several nights since moth flies may not emerge every day. Check less obvious spots like air conditioning drip pans, sink overflow drains, and floor drains in utility areas. Water stains or musty odors may point to hidden moisture problems where moth flies could breed.
Mechanical Cleaning
Removing the organic film is the most important step in moth fly control. Chemical treatments alone cannot get rid of the slimy layer where larvae grow.
Use a stiff drain brush to scrub inside drain pipes. Focus on the drain opening, the crossbars of the drain cover, and the first few inches of pipe where buildup collects. For garbage disposals, run the unit with ice cubes and coarse salt to clean interior surfaces.
For floor drains, remove the grate and clean both the trap and visible pipe surfaces. Flush all cleaned drains with hot water to wash away loosened debris.
Biological and Chemical Options
Enzymatic or bacterial drain cleaners can supplement mechanical cleaning. These products contain bacteria that break down organic matter in pipes. They work over several days and are most useful as ongoing maintenance after the initial cleaning.
Insect growth regulators and residual insecticides can be applied to surfaces where adult flies rest. However, these treatments only provide short-term relief if breeding sites remain. Products containing Bacillus thuringiensis israelensis (Bti) can target larvae in breeding sites.
Avoid using bleach or harsh chemical drain cleaners as your main treatment. They may kill some larvae on contact, but they do not remove the organic film. Repeated use can also damage pipes.
Prevention Strategies
After getting rid of an active problem, regular maintenance keeps moth flies from coming back:
- Run water through all drains at least once a week to flush organic buildup
- Clean drain stoppers, strainers, and overflow holes often
- Use enzymatic drain treatments monthly to prevent buildup
- Fix plumbing leaks quickly to remove moisture sources
- Make sure air conditioning drip pans drain well and clean them regularly
- Fix any moisture issues in basements, crawl spaces, or behind walls
When Professional Help May Be Needed
If moth flies continue after thorough drain cleaning, the breeding source may be hard to reach. Broken sewer lines under the foundation, damaged septic parts, or buildup in main drain lines may need a professional inspection with a camera to find and fix. Moisture problems inside walls or under floors may also need professional help.
References
Other Flies
Explore other species in the flies family
Commonly Confused With
Moth Flies are often mistaken for these similar pests
Where Moth Flies Are Found
Hover over states to see their names. Green regions indicate where moth flies have been reported.
Common Questions about Moth Flies
What are moth flies?
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Moth flies are small, fuzzy flies in the family Psychodidae that look similar to tiny moths. They are also commonly called drain flies, sewer gnats, or filter flies. These insects breed in the organic film that builds up inside drains and other moist areas.
Why are they called moth flies?
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Moth flies get their name from their fuzzy, moth-like appearance. Both their bodies and wings are covered with tiny hairs, giving them a furry texture that resembles small moths. However, they are true flies with only two wings, not moths.
Do moth flies bite or spread disease?
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No, moth flies do not bite humans or pets. They are primarily a nuisance pest. However, in large numbers, their shed body scales and wing hairs can become airborne and may trigger allergic reactions or respiratory issues in sensitive individuals.
Where do moth flies come from?
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Moth flies breed in the slimy organic film that accumulates inside drains, pipes, and other areas with standing water and decaying organic matter. Common breeding sites include bathroom drains, kitchen sinks, floor drains, and air conditioning drip pans.
How do I get rid of moth flies?
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The most effective way to eliminate moth flies is to remove their breeding source by cleaning drains thoroughly with a stiff brush. Simply pouring chemicals down the drain will not remove the organic film where larvae develop. Regular drain maintenance prevents reinfestation.
How long do moth flies live?
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Adult moth flies typically live for about two to three weeks. However, their complete life cycle from egg to adult takes only 8 to 24 days depending on temperature, allowing populations to grow quickly when breeding conditions are favorable.
Can moth flies infest my whole house?
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Moth flies typically remain close to their breeding sites and do not spread throughout homes like some other pests. If you see them in multiple rooms, there may be multiple breeding sites such as different drains or hidden moisture problems that need to be addressed.
Are moth flies the same as drain flies?
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Yes, moth flies and drain flies are the same insect. Both names refer to members of the family Psychodidae. They are also sometimes called sewer gnats, filter flies, or sink flies depending on the region.
With five years of hands-on experience in the pest control industry, George Schulz is a registered technician with the Virginia Pest Management Association and a proud third-generation professional in a family business that's been protecting homes for over 57 years. He manages and trains a team of service pros while also leading internal research efforts—recently spearheading a deep-dive review of thousands of documents on pest control materials to hand-pick the most kid and pet friendly, most effective solutions tailored specifically for homes in the DC metro area.