Drain Flies & Drain Mites

Drain Flies or Drain Mites are a very small fly that feed on waste matter within sewers and drains, they can however infest a property given the correct circumstances and no amount of fly spray will halt the infestation unless you can find their point of ingress or their food source and do something about it.

Click the image to the right and you will see a short video file showing the activity downstream of a partially blocked drainage system.

The vast majority of domestic drainage systems are fairly clean in as much as they are designed to carry waste from one point to another and there should not be any waste sitting in the system, but due to defective pipe work or partial blockages this can happen providing a food source for the pests. However drainage systems are also designed so that no matter what occurs below ground these flies should not have access to your property and sinks, baths, toilets etc are fitted with water traps to prevent smells and pests from leaving the drainage system and entering your home.

So if you have an infestation of drain flies within your bathroom there are usually a couple of things happening, firstly waste matter is building up either within or outside the drainage system allowing the flies to feed and breed, if this is occurring within the drainage system they are also finding an open vent out of the system and into your property. The life span of these pests is pretty short but they will lay eggs in your property and before long the next generation are swarming over your bathroom fixtures and fittings.

Typical Drain Fly Infestation Scenarios

The most common and probably the most disturbing for the home owner is when you have an internal rest bend at the base of a soil vent pipe or downstairs toilet, the rest bend fractures or becomes displaced and after every flush a certain amount of water and waste escapes into the sub-floor. The matter builds up and the flies have a food source, they will then access the property above through any small gaps between floor boards or gaps local to skirting boards.

The above can also occur when small diameter waste pipes from sinks are suspended from joists in sub floors, if these pipes become disconnected or leak there is enough food stuff, grease & fat in the water for the flies to feed off.

Disused branch lines on drainage systems can often hold waste matter if the system has blocked or partially blocked at any time, because of its location below ground the waste will not dry out immediately and this can provide a steady and prolonged food source for the mites. If this disused branch line runs beneath and extension or conservatory and it has not been capped off properly the flies will find their way into the property.

Leaking and broken pipe work outside of the property can also allow the flies to enter the house, a cracked collar at the base of a soil vent pipe (see image to the right) or a fractured gully pot that cannot maintain its water level will allow the flies to surface at ground level, if this occurs local to an air brick they have access direct into your sub-floor and wall cavity.

Restaurants and industrial kitchens can be prone to this kind of infestation due to the amount of food stuffs that can directly enter the drainage system and the worst case of infestation i have seen was at a hospital. This was partly due to a construction worker leaving a drain open within the building and partly due to the fact that hospital staff used the bed pan macerators for the disposal of excess food instead of using the appropriate food bins supplied.

How To Stop Drain Fly Infestation

Its critical that you find the source of the problem rather than just trying to exterminate each wave of the blighters, they don't tend to move too far from the point of access so its worth studying there movements , if you have a sub-floor its always worth lifting a couple of boards and checking for standing water and waste matter. Get the drainage system checked out and cleaned, a drain camera inspection can also locate any defective pipe work or any disused connections.

Once the source of the problem has been located and dealt with you can get the problem area fumigated to deal with the remainder of the enemy, safe in the knowledge that they will not return.