This week, a colleague complained about a new pest in her home: drain flies. They’re a similar size to fruit flies, but fuzzier and more moth-like, and – if the name didn’t give it away – they tend to hang around the drains. These pests are notoriously difficult to get rid of and are just as likely to infest a clean and tidy house.
I did a little research and found out that drain fly activity spikes in the summer months, driven by the heat and humidity. But, given that it’s now almost September, why are they still around and how is it that they keep coming back? I spoke to Eliot Moakes, owner and pest control technician at Pest Control Leicester, to find out why drain fly activity is still going strong, and what you can do about it.
Why are drain flies suddenly surging?
‘Drain fly activity increases during periods of warm and humid weather, just like the UK has been seeing recently,’ says Eliot. ‘This is because the warmer temperatures speed up their breeding cycle. If we have a warm end to summer, then the conditions inside drains can remain suitable for them for longer than people might expect.
‘Warm and humid conditions that are combined with standing water and organic matter inside drains create an ideal environment for drain flies to breed.’
So, the hot, dry summer most of us have been having is to blame for the persistent drain flies. They’re on the hunt for residue inside our drains that can feed their larvae. That includes bacteria, rotting food, soap scum as well as hair – really any kind of organic matter that can lead to blocked drains. That means bathroom drains are as much at risk as your kitchen and utility drains.
Once a female drain fly finds a suitable drain – one filled with slimy residue – she lays up to 100 eggs at a time just above the waterline of the U-bend, which take up to two days to hatch and from one-two weeks to fully mature into adults. As adults, they feed on moisture or flower nectar. While drain flies won’t bite you, they can transfer bacteria from the drain to whatever surface they touch.
What attracts drain flies
Eliot continues: ‘Drain flies are attracted to damp areas containing decaying organic matter. They're not always necessarily coming into the house from the outdoors because I've found in many cases they're already breeding somewhere within the drainage system and coming through the pipes.’
So, closing windows and fitting fly screens might not help when it comes to stopping drain flies. They already have access to your home via your drains. And the slimy residue on the walls of your pipes is what’s luring them in.
‘Anywhere with drains that aren’t used regularly are the places I’d take a look at first, such as bathrooms, kitchens and utility rooms,’ advises Eliot. ‘The shower drains, floor drains and rarely used sinks can be particularly suitable because moisture and organic material are allowed to build up undisturbed.’
Standing water is a major attraction for drain flies because it means bacteria is more likely to thrive for larvae to feed on. If your home has any rarely used drains or even leaky pipes, roaming drain flies will take an interest. Mould and musty smells could be a key indication of dampness.
How to get rid of drain flies
Drain flies are a nightmare to get rid of because, even if you kill the adults, the larvae will survive and start the cycle all over again.
Eliot says: ‘The key is finding and removing the breeding material rather than just killing the flies you can see. The affected drain needs to be thoroughly cleaned, particularly around the inside of the pipe where organic build-up can accumulate. Pouring products down the drain without physically removing that build-up may only provide temporary relief.’
Boiling water will kill both the adult drain flies and their larvae, but it won’t remove the slime that’s feeding them. That means the problem can easily come back. We also wouldn’t recommend tipping boiling water down household pipes as it can damage the plastic components and joints. It's one of the many things you need to stop pouring down the sink.
It’s also illegal to pour insecticides down the drain, for risk of contaminating groundwater and harming aquatic life.
So, what should you do?
‘You need to keep drains clean and flowing properly, deal with standing water and regularly run water through drains that aren't used very often,’ Eliot surmises.
We recommend first removing obvious blockages using a long, thin drain snake. Once the pipe’s clear, you need to tip an enzyme-based drain cleaner down it to dissolve any remaining residue. This should clear the immediate slime from your pipes.
Going ahead, you need to keep stagnant water moving by making sure seldom-used toilets and drains are flushed regularly. You can also apply enzyme sticks to dissipate future grease, or alternatively there’s the option of tipping 125g of bicarb down drains, followed by 125ml of distilled white vinegar to refresh them. We recommend doing this monthly. If that doesn’t solve your drain fly problem, you may need to bring in a professional to help locate potential sources of stagnant water.
Drain fly removal kit
