Drain Flies: Blocked Drain Causes and More Info


Drain flies, or moths or sewer flies, are small insects often found near drains, sinks, and other moist areas in homes and buildings. At first glance, the flies look harmless. However, they contribute to the formation of drain flies in blocked drain, leading to plumbing issues and potential health concerns. Understanding the biology and behaviour of drain flies is crucial in preventing and addressing drain blockages caused by these insects.

Understanding Drain Flies

Drain flies are typically 2-5 millimetres in size and have a distinctive appearance, with fuzzy bodies and wings that resemble those of moths. They are attracted to the moist, organic matter accumulating in drains, pipes, and other damp areas. Their life cycle includes eggs, larvae, pupae, and adults, all of which can contribute to the formation of blocked drains.

Drain Fly Reproduction in Blocked Drains

Drain flies are attracted to the moist, organic matter that can accumulate in drains, pipes, and other damp areas. In a blocked drain, these conditions are ideal for their reproduction. Females can lay up to 100 eggs simultaneously, hatching into larvae within 48 hours. The larvae then feed on the decaying organic matter, further contributing to the buildup in the drain. This cycle can repeat quickly, with the adult flies emerging in as little as 9-15 days, depending on the temperature. The rapid life cycle of drain flies allows them to establish large populations quickly, exacerbating the drain blockage problem.

How Drain Flies Contribute to Blocked Drains

Organic Matter Buildup

Drain flies feed on the slime, hair, and other organic matter that can collect in drains over time. As they lay their eggs and their larvae develop, they contribute to the buildup of this material, which can eventually lead to partial or complete blockages. The larvae of drain flies are particularly adept at breaking down organic matter, further exacerbating the problem.

Biofilm Formation

Drain flies can also help facilitate the formation of a slimy biofilm on the interior surfaces of pipes and drains. Bacteria and fungi are just two of the many microbes that make up this biofilm, which can exacerbate the problem by entangling more debris and blocking the water flow. The presence of drain flies can accelerate the growth and spread of this biofilm.

Clogging with Larvae and Pupae

The larvae and pupae of drain flies can physically block water flow through the drain, causing it to back up and overflow. As the larvae grow and develop, they can form dense masses that completely obstruct the drain, leading to water accumulation and potential flooding.

Common Causes of Drain Flies in Blocked Drain

These flies are most often the result of a clogged drain or sewer line, where the buildup of organic matter, hair, and other debris limits the wastewater flow. This stagnant water serves as the ideal breeding ground for these pests. Other common causes of blocked drains that can attract drain flies include:

1. Unused toilets

2. Refrigerator drain pans

3. Leaking pipes

4. Sinks and tubs with infrequent use

5. Improperly maintained septic systems 

Identifying and Addressing Drain Fly Infestations

If you suspect a drain fly problem in your home or building, look for the following signs:

1. Seeing small, moth-like insects near drains or sinks

2. Noticing a musty or sewage-like odour coming from drains

3. Observing a buildup of organic matter or a slimy film in the drain

4. Experiencing slow drainage or water backing up in sinks or showers

Drains More Prone to Blockages by Drain Flies

Certain types of drains are more susceptible to blockages caused by drain flies due to their design and the materials they are made of:

Older cast-iron or galvanised steel drains

These materials can rust over time, creating crevices and rough surfaces that allow organic matter and biofilm to accumulate. 

Horizontal or slow-moving drains

Drains with a gentle slope or low water flow are more prone to buildup and stagnation, providing ideal conditions for drain fly breeding. 

Drains in bathrooms and kitchens

These areas often have higher levels of organic matter, hair, and food debris, which can attract and sustain drain fly populations. To effectively address and prevent drain fly infestations, it is crucial to identify and address the underlying causes of blocked drains, such as poor plumbing design, infrequent maintenance, or improper waste disposal. Regular cleaning, drain maintenance, and prompt action when signs of an infestation appear can help mitigate the long-term effects of this persistent pest problem.

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