Drain Fly/Moth Fly

Drain Fly/Moth Fly

Scientific Name: Family Psychodidae

How to identify a drain fly

Drain flies are also known as Moth flies, sink flies, filter flies, sewer flies, or sewer gnats.

Adult drain flies are tiny (4-5mm long), fuzzy, dark or greyish insects with the body and wings densely covered with hairs. They have long antennae. Wings, appearing too large for the body, are held roof-like over the body when at rest, giving a moth like appearance. They are weak fliers and make irregular, hesitating flights covering only a metre or so in short, jerky lines and are most active during the evening.

Where are drain flies commonly found?

Adult flies may become very numerous at times indoors especially around drains, in urinals, on toilet/bathroom walls and around showers and bathtubs and often as a result of blocked or broken drains. Drain flies can also be found in sewers, piles of compost and damp leaves, grass and decaying trees.

Why are drain flies considered a pest?

They do not bite, sting, or spread diseases, but their decaying bodies may cause allergic reactions. They can also spread bacteria from trash, decaying vegetables and fruits. Drain flies breed in areas that are moist and have a lot of organic matter. They are more of a nuisance pest than anything else.

What is the biology and lifecycle of a drain fly?

Drain Fly undergo complete metamorphosis during their life cycle. Eggs, laid by females hatch into pale-colored larvae. Following a feeding period, larvae pupate and soon emerge as adult flies. Adults live only 3 to 4 days without food, but they can survive for weeks if nectar or other liquid carbohydrate food sources are available. Typically, drain flies complete their life cycle in 21 to 27 days but this accelerates at higher temperatures.

Management Tips for Drain Flies

  • Inspect drainage for problem – ensure there is no broken or blocked drains.

  • Cleaning drains using products that contain enzymes will remove mould and organic matter from drains so eliminate breeding sites for drains flies.

  • Pouring boing water down drains several times a day for a couple of weeks

  • Physically clean the drains in some way


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