Tips and Ideas

Control of Midge Flies

Posted: Friday, November 06, 2009
By: Control ideas assembled by Ron Altmann

Below are a few suggestions for controlling Midge flies. I can't say there is any "one" good way of controlling the pesky flies, and what works at one wastewater plant, may not for another. I'll admit some ideas don't sound very practical (such as adding defoamer) but I did include them just incase someone could find an application. Good luck.

Bacillus Thuringuensis (BT) bacteria
Christopher Helgestad provided a wealth of information on a biological agent that uses bacillus thuringiensis bacteria (BT) to disrupt the reproduction cycle. The product he used is called Mosquito Dunks manufactured by Summit Chemical out of Baltimore, MD. Chris bought a card of twenty disks for $40.00 (2003 price), from a distributor in Wausau (phone: 715-849-1043) and provided a national distributor out of Columbus, Nebraska (phone: 1-800-228-8508). I have heard of this product before and there seems to be more then one manufacturer of the bacteria. Some are floating disks and others are rectangles. To apply BT in wastewater plants, place them within small cages or tie the disks to a rope and put them in filters, clarifiers, and aeration splitter boxes. They slowly dissolve their active ingredient and dose the water.

Wastewater operators have had success with this product. Others are afraid to use it because it is a chemical agent and may cause failure of WET testing. One operator could not get his area DNR rep. to sign off on the products use. Application at Oconomowoc was suggested at 3 lbs. to each filter a month. A supplier was given by Dick Bacon at the Oconomowoc WWTP: Smith Ecological Systems in Rockford, Illinois (phone: 815-968-8079). They will help with your questions and dosage rate.

Adding a defoamer
This has worked for mosquito control and has been suggested for midge flies, but I don't know of anyone that has had success. Possibly, it could be added to a clarifier surface and with the skimmer raised it could help in control. If you give it a try please let us know if it works. The theory is that the defoamer changes the surface tension of the water so the mosquito larva cannot penetrate the surface to breathe and thus drown.

Wastewater plants have used chlorine and hosed the surface of the water with this solution. Others have thrown in HTH (I suppose a floating device could be made so the HTH would dissolve on the surface). Some have stopped the flow to a filter or clarifier while dosing for a better kill and to give time for the chlorine to dissipate.

Commercial grade 7-Dust
This product comes dry and is made into a slurry then hosed or sprayed on the ground. The midge fly must somehow be attracted to it and die. It is not permitted for use where the effluent may contact the water supply. Sorry to say that's all the information I have on the product. If you know more please send an e-mail.

Electric bug zappers
This has been successful in covered clarifiers.

Turning off outside lighting
Of course, the tiny flies are attracted to light. When conditions are bad, some plants turn off the outside lighting, especially in the early evening.

Fathead minnows and goldfish
These have been used in traveling bridge sand filters and in clarifiers. As with attracting bats and swallows, this is a natural way of controlling midge flies. The addition of chemicals can kill off natural enemies that feed on the midge larvae.

Mixing the upper level of the clarifier
Midge files have a life cycle of; 4 days larvae, 3 days worms, and 4 days adult. In the adult stage they only fly around, reproduce, and become a nuisance. When in the larvae stage, they can live in the upper levels of a clarifier where there is not much water movement. You may notice high populations of midge larva in your clarifier and after high flows or a windy day they are gone. They are being moved out of the clarifier by the water movement. If the upper layer of the clarifier stratifies, it's midge heaven. With warmer temperatures and no currents, the upper layer also promotes algae growth. This provides food and oxygen for the larvae. Breaking up that layer may help "push" them out of the clarifier (and into your sand filters). Using a water hose to break up the stratified layer may help.

Bat houses and swallows
A plant put up bat houses and had success with attracting bats to control the flying midges. Search the Internet for "Bat houses" if you need more information on building them. Brockton Wastewater plant in Massachusetts tried to import a genus of swallows. This wasn't very successful after a few years. (Guess the swallows flew the coop.) Again, this is a natural way of controlling midge flies. Chemicals can kill off natural enemies that feed on the midge larvae.

Some Midge fly facts:
- Larvae resemble worms and are bright red. That's why they are called bloodworms.
- The adult midge fly beats its wing 950 time per sec. (Hummingbirds only beat their wings at 75 beats per sec.)
- The adult fly is attracted to light
- Midge larvae feed on algae