HomeIPM Plans
Drain Fly

Drain Fly

This document contains information about the biology and management of flies that commonly live in the gelatinous material that collects on the sides of drains and other areas high in moisture and organic material. A range of management options is listed. From this list, the IPM Practitioner can choose options to develop a unique management plan for each particular customer site.

General Information


Management Objectives for the Pest at the Particular Site

What do you want/need to accomplish at the site in regard to the pest flies?

The answer to this question will vary, depending on the site and the customer. Some examples are

  • Reduce fly complaints in the building and work with occupants to prevent future complaints
  • Keep flies out of food handling and food processing areas
  • Help customer comply with Health Department regulations


Drain Fly Identification

  • These flies are in the family Psychodidae and are also called “moth flies” or “filter flies”.
  • Adult drain flies are tiny (less than 1/4” long), and fuzzy-looking.
  • Adults hold their fuzzy wings over their bodies like a tent.
  • Adults are poor fliers and fly only a few feet at a time.
  • The wormlike larvae (maggots) of drain flies are legless, gray, and about 3/8”.


Why Drain Flies are Considered Pests

  • In small numbers, drain flies are mainly a nuisance pest.
  • The larvae are considered beneficial because they are an important part of the group of organisms that break down and recycle organic matter.
  • In large numbers, drain flies can fall onto and contaminate food, eating utensils, and food preparation surfaces.
  • In large numbers, their constant presence can be annoying.
  • Although they are of no significant medical importance, they can cause respiratory problems in people who must live and work in clouds of flies.


Special Regulatory Conditions

California Health and Safety Code Sections that relate to cleanliness in food establishments:

114010. “All food shall be prepared, stored, displayed, dispensed, placed, transported, sold, and served as to be protected from dirt, vermin, unnecessary handling, droplet contamination, overhead leakage, or other contamination.”

114030. “A food facility shall at all times be so constructed, equipped, maintained, and operated as to prevent the entrance and harborage of animals, birds, and vermin, including, but not limited to, rodents and insects.”

114040. “The premises of each food facility shall be kept clean and free of litter, rubbish, and vermin.”

114050. “All food facilities and all equipment, utensils, and facilities shall be kept clean, fully operative, and in good repair.”

Biology and Behavior

To be successful, management strategies must take into consideration the biology and behavior of the pest. Understanding the biology of a pest can reveal weaknesses and vulnerabilities that can be exploited when trying to manage the pest.

General Biology of Drain Flies

All flies have 4 distinct life stages: egg, larva (commonly called maggot), pupa, and adult.

  • An adult female drain fly lays irregular masses of 10 to 200 eggs in areas with moist organic material suitable for larvae to feed on, such as:
  • drains
  • areas where broken drains have leaked
  • garbage disposals
  • condensate pipes for air conditioners
  • condensate lines for icemakers
  • toilets, especially if used frequently
  • loose tiles in kitchens where water and debris collect
  • moist or wet and dirty garbage receptacles
  • moist mops and mop buckets
  • sauces under potted plants
  • moist compost
  • clogged storm drains
  • damaged or faulty septic lines
  • septic tanks
  • sewage filtration tanks
  • areas with sewage leaks or back-ups
  • areas where water collects and mold and algae grow (condensate pans under refrigerators, low lying areas next to buildings, beneath air conditioning units on roofs, tree holes)
  • Eggs can hatch in less than 2 days.
  • Larvae are capable of surviving temperature extremely and low-oxygen environments.
  • In 9 to 15 days when the maggots are ready to pupate, they do so on or in the material they have been eating.
  • Adults live only 3 to 4 days without food.
  • Adults can live for weeks if nectar, polluted water, or other liquid carbohydrates are available.
  • Adults are small enough to pass through ordinary window screening
  • Adults can breed in large number at sewage treatment plants, and then, carried on the wind, can invade other sites up to a mile away.


Feeding Behavior of the Drain Flies

  • Adult drain flies feed on nectar or other liquid carbohydrates.
  • Larvae feed on bacteria, fungi, algae, and other microorganisms associated with decaying organic matter.


Factors that Favor Drain Flies

  • Unclean drains where gelatinous film is allowed to accumulate
  • Very moist or wet food residues left in garbage cans and dumpsters
  • Poor sanitation in kitchens and bathrooms where broken or loose tiles, holes in baseboards and floor, or other conditions provide areas for organic matter to collect
  • Broken or leaking sewage or drain pipes
  • Allowing excess moisture to collect in combination with organic matter
  • Poorly cared-for compost piles or bins can produce many kinds of flies.


Monitoring and Record Keeping

The purpose of monitoring is to track pest activity in order to catch small problems before they become overwhelming. Monitoring makes it possible to pinpoint pest activity so treatments can be targeted. Monitoring also makes it possible to properly time pest management actions and to evaluate the effectiveness of those actions. Records are kept to document the methods and products used and to record information that can be used to fine-tune pest management methods and plan future actions.

  • Black light traps and visual inspection of likely breeding sites are useful monitoring techniques.
  • A glue board can be set atop a cylindrical collar and then placed over a drain to monitor for the presence of drain flies. This should be done at night when the flies are most active and the drains are not being used.


Tolerance Level

The “tolerance level” is the number of flies that triggers action to control the pest. The tolerance level is site-specific and differs depending on the customer, the location, and other factors. Determining the tolerance levels for a site helps prioritize work that must be done to control the pest.

Management Strategies

To manage drain flies, it is most effective to concentrate on eliminating conditions that support the immature stages (maggots). This involves proper maintenance, sanitation, and disposal of food wastes as well as keeping waste receptacles clean and dry. Many of these sanitation practices will prevent problems with other insects as well.

Habitat Modification

To limit availability of food

  • Discuss the importance of sanitation with the appropriate people.
  • Keep kitchens and bathrooms clean; periodic deep cleaning is recommended, especially for kitchens and food preparation areas.
  • Keep kitchens and bathrooms in good repair to eliminate loose tiles, holes, cracks, and crevices that can accumulate organic matter.
  • Drain food wastes before placing in a plastic bag for disposal in a waste receptacle or dumpster.
  • Use plastic liners in all waste receptacles that might collect food garbage; seal the plastic liners before placing in outside dumpsters or garbage cans.
  • Remove garbage containing food wastes from the building before nightfall or tie a knot in the plastic liner.
  • Store garbage in closed, rodent-proof dumpsters or garbage cans outside the building and away from doors.
  • Keep waste receptacles and dumpsters clean and dry; use a high-pressure stream of water or a brush and soapy water. Rinsing with a mild solution of borax or baking soda and water will eliminate odors.
  • Allow to dry thoroughly before using.
  • Inventory drains in the building and make a cleaning schedule. Clean drains with brushes, steam, and/or water.
  • Promptly fix drains or electric garbage disposal units that leak or drains that allow food waste to accumulate under sinks or floors. This food waste will attract many different kinds of flies.
  • If drains or garbage disposal units do leak food waste, remove all the food waste and clean the area thoroughly.
  • Keep toilets clean, especially those that are little used.
  • Promptly fix septic or sewer lines that are faulty or broken.
  • Hang mops and booms on a rack on the wall to dry; do not leave on the floor or in a bucket.
  • Keep mop buckets clean and dry when not in use.
  • Maintain compost piles properly, otherwise they can produce large numbers of many kinds flies.
  • Prevent excess moisture from accumulating and standing for long periods.


Chemical Controls

  • Chemical controls are not recommended for drain fly control.


The IPM Partnership


The PCO-Customer Partnership is Very Important

IPM works best when the customer and Pestec form a partnership to tackle the pest problem. Drain flies cannot be managed satisfactorily without the cooperation of the customer, especially in the area of sanitation. Pestec will discuss the findings of the initial inspection and any subsequent monitoring sessions with the customer to determine which issues and tasks will be the responsibility of Pestec and which will be the responsibility of the customer.


Information is a powerful tool in IPM. Information can help change people’s behavior, particularly in how they store food and dispose of waste. Changing these behaviors is a necessary part of managing flies. Occupants of buildings and homeowners can also help in the early detection of pests so that Pestec can be alerted before the problem is severe.

Pestec’s highly trained and knowledgeable staff can provide pest management education or training sessions for facilities managers, risk managers, building occupants, homeowner associations, and others.