A drain fly infestation will become noticeable when a significant number of adult drain flies are present. In most cases, drain flies can be found resting on bathroom walls or near breeding locations. A drain fly infestation can easily become troublesome when the population becomes excessive.

Most drain fly infestations occur in moist areas and near organic materials. As the name would imply, drain flies are normally found in storm or home drains. However, compost piles and decaying logs are two other locations that make great breeding grounds for drain flies. Although homeowners can take action and try to remove a drain fly infestation, it might be a better idea to seek professional help.