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Sticker of Trickling filter fly
Bug card No. 4424 of 4,939

Trickling filter fly

Psychoda alternata

The trickling filter fly is a tiny, fuzzy fly that you might spot in a bathroom near the drain. Its broad grey wings are covered in little hairy tufts, so it looks like a tiny moth. It is not a strong flier and mostly runs or hops about.

Lives in
First from North America, now around the world, near drains and sewage works
Length
4 mm (0.16 in)
Top speed
about 5.7 km/h (3.5 mph)
Flying, estimate
Can it hurt you?
Harmless
Harmless. It does not bite or sting. It is just a bit of a nuisance in the bathroom.
What does it eat?
Its larvae live in slimy ooze in drains and sewage pipes and feed on the rotting stuff there.
For real!Photo of Trickling filter fly
Picture by Victor Engel. CC BY-SA 4.0, via Wikimedia Commons.

How big is it?

How long is it?

Trickling filter fly about 4 mm long (0.16 in)A grain of rice about 6 mm (0.24 in)
small enough to sit on your fingernailcould fly across a whole football pitch in 66 secondsmoves 400 times its own body length every second

How big is Trickling filter fly compared to YOU?

Just maths in your browser. Nothing is saved or sent anywhere.

How fast is it?

cool stuff

Fun facts

1

Its larvae help clean dirty water. At sewage works, water trickles over stones covered in tiny living things, and the fly larvae are part of this cleaning team.

2

A female can lay up to 100 eggs, often in sticky little bundles.

3

The eggs hatch in about two days, and the larva grows up in about 15 days.

4

The males only live a few days, and the females about a week.

5

The grown-up flies hardly ever go far from the place where they hatched.

you asked

Most asked questions about Trickling filter fly

?Where do drain flies come from?

Their larvae grow up in the slimy ooze inside drains and sewage pipes.

?Are drain flies dangerous?

No. They do not bite or sting. They are only a nuisance.

For bug experts

Scientific name
Psychoda alternata
Group
Flies and mosquitoes
Family
Psychodidae
Classification
Insecta > Diptera > Psychodidae
Lives on
North America, Europe, Asia, South America
Also known as
Drain fly

Where the facts come from

  1. Psychoda alternata (Wikipedia, CC BY-SA 4.0): what it looks like, where it lives, what it eats, sizes and fun facts, retold in simple words.
  2. Picture by Victor Engel. CC BY-SA 4.0, Wikimedia Commons. The sticker of this bug is drawn from this picture.

If we got something wrong, sorry, we are bug fans, not a science journal. Tell us at [email protected] and we will fix it.

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