Drain Flies

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. 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 can 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 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.


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 it’s worth studying their 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.



Drain Fly Larvae

It is not uncommon for homeowners to report black or dark-colored worms in their sink drains or toilet bowls. These are actually not worms at all but the larval maggot form of the drain fly. Drain flies are known for their love of moist environments. Adults are drawn indoors because they detect a water source; contaminants in that water source such as bacteria, fungi, decaying organic matter, sediment and the like are one of the principal food sources of the drain fly, so contaminated; standing water is a favourite breeding ground for drain flies.



The easiest way to remove drain fly larvae from the toilet bowl is to simply flush the toilet. But keep in mind that something in the toilet water drew the drain flies in the first place, and a re-infestation is likely if you don't take steps to remove the water contaminants the attracted the adult flies to breed in the toilet water. After flushing the larvae down the toilet, monitor the toilet water for a few days to see if adult flies breed in the water again. If they do not, the infestation was likely a one-time occurrence. If drain fly larvae appear in your toilet water again, however, further action is required.


Preventing Future Infestations

First, deep clean the toilet bowl and surrounding surfaces and see if the drain flies return to breed in the toilet again. If they do, there may be decaying organic matter or another water contaminant deep in the toilet drain. Use a long-handled toilet brush or plumber's "snake" to clear out any contaminants that are deeper in the toilet drain. You may also need to use a bacteria complex cleaning agent such as DF 5000 gel to breakdown organic matter that may be attracting he drain flies.


Other Considerations

Drain fly infestations are more common during extended periods of inactivity that leave puddles of water standing for some time. For instance, homeowners often report drain flies in the home after having been on vacation, during which puddles of water have collected in kitchen and bathroom sink drains and have been left standing long enough to be contaminated. Therefore another important component of preventative drain fly control is to make sure water is not left standing in the home for any period of time.