Lagoon Bloodworms: How to Control Chironomids and Midge Flies

lagoon midge flies

Lagoon bloodworms are the larvae of midge flies and are common during warm summer temperatures. Midge flies swarm and can drive local residents indoors. Lagoon bloodworms provide insight into lagoon conditions and their effect on effluent quality. Read on to learn why they appear, what they indicate about lagoon conditions, and how to control them.

Lagoon midge flies hatch from bloodworms

An operator in Georgia shared with us the following video, which shows lagoon sludge swarming with wriggling bloodworms.

Bloodworms or red worms are the larvae of midge flies. Midge flies or chironomids are also called “blind mosquitoes” because they resemble mosquitoes but don’t bite. According to Wikipedia, they have a number of regional nicknames, too: In Canada, they’re called lake flies; near Green Bay, Wisconsin, they’re called bay flies; around the Great Lakes, they’re called muffleheads or muckleheads; and in Florida, chizzywinks. No matter what you call them, they’re a nuisance.

lagoon midge flies

Although they don’t bite like mosquitoes, midge flies swarm, in masses of tens of thousands per square meter. They create a nuisance by congregating around light fixtures and screens, flying into mouths and noses and eyes and ears, staining the surfaces they land on, and driving people indoors. While midge flies don’t transmit disease, they can cause an allergic reaction, especially in sewage workers. A wastewater lagoon breeding midge flies near a residential area is going to have unhappy neighbors.

Midge fly larvae can also end up in the water supply, as some residents of Texas learned in the summer of 2015, when tiny bloodworms emerged from faucets and sprinkler heads.

Why are midge flies attracted to lagoons?

A wastewater lagoon is similar in many ways to a natural aquatic environment and, hence, is attractive to bloodworms and midge flies. Facultative lagoons, especially ones that are in poor condition, are heaven to midge flies and can cause them to reproduce to bothersome levels.

Midge flies like to lay their eggs in quiet waters, so a floating algae or scum mat at the edge of an insufficiently mixed or circulated lagoon is perfect. If the lagoon is not optimally maintained, so much the better: the overgrowth of plants and vegetation interferes with the wind and wave action across the surface of the water that could disrupt them.

The clumps of midge eggs either attach to the surface mats or in-lagoon fixed media, or sink to the bottom of the lagoon, where the hatchling bloodworms feed on bottom sludge and bacterial floc. This floc consumption can derail treatment, as outlined in a profile published in TPO Magazine of an activated sludge package plant with a bloodworm infestation.

In addition, bloodworms either outcompete or consume nitrifying bacteria, which can cause effluent ammonia levels to spike. (While Triplepoint’s NitrOx Process uses media to cultivate nitrifying bacteria, the media are in constant motion and thus don’t provide a habitat for bloodworms.)

After a couple of weeks, the bloodworms pupate and emerge from the surface as midge flies to begin the reproductive cycle again.

What do lagoon bloodworms reveal about conditions?

Like other lagoon conditions we’ve discussed, such as color and odor, the presence of midge flies and bloodworms offers clues to the overall health of the lagoon system.

Mats, sludge, and floating solids: If you can see bloodworms, you’re also going to see algae or rotting plant matter, sludge, or scum. Midges lay eggs on mats of algae or scum on quiescent waters, often at the edges of facultative lagoons. Turbulence at the surface, even from wind and wave action, keeps midge larvae in check. Bloodworms consume algae, sludge, and decaying vegetation, so offering them a buffet encourages them to reproduce.

Odors: The conditions that encourage midge flies to breed, namely decaying algae mats, floating sludge, and stagnant water, are also the conditions that create foul lagoon odors.

TSS: Algae is the main contributor to high Total Suspended Solids in lagoon effluent, so if you have enough algae to create a haven for midge flies, you likely have a TSS issue. In addition, midge flies are prolific reproducers and lay thousands of eggs at a time in a gelatinous, sticky mass, which can further contribute to effluent solids.

DO: The presence of bloodworms doesn’t provide much insight into dissolved oxygen conditions. They enjoy the high DO near the surface, but are tolerant of low DO at the bottom.

Nutrients: Midge fly larvae like nutrient-rich environments, so rampant bloodworm populations may flag high Ammonia and Total Nitrogen levels in your lagoon. (Read our blog on Wastewater Lagoon Nutrients: The TL;DR of TMDL for more on this subject.)

How to prevent or remove lagoon midge flies and bloodworms

To prevent bloodworms and midge flies from taking over a lagoon, prevention is key. Clear away any vegetation or structures that are preventing wind contact with the water’s surface.

For severe infestations, biological augmentation or chemical intervention may be necessary. In The Biology and Troubleshooting of Facultative Lagoons, author Michael Gerardi recommends Bacillus thuringiensis to control midge and mosquito larvae, but cautions that larvicides should only be used as a last resort, and only with the permission of regulatory agencies. He also suggests predatory bottom-feeding fish like carp and Gambusia to consume midge fly larvae.

The Wisconsin Wastewater Operators’ Association offers a number of additional suggestions for midge fly control, including bug zappers and predators like bats and swallows.

lagoon midge flies
Surface turbulence prevents midge flies from reproducing in the lagoon.

The best way to avoid bloodworm infestation is to make sure the lagoon is properly mixed and circulated. Robust mixing and surface turbulence create an inhospitable environment for midge flies to breed, and prevent the algae growth that serves as their food source.

Download our Ares Aeration®­ brochure to learn more about how aeration and mixing can prevent the conditions that lead to poor effluent quality.

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