Preventing a Bloodworm Invasion

Midge fly infestations can pose considerable challenges for activated sludge systems and lagoons. Also known as Chironomids or bloodworms in their larvae stage, these insects resemble mosquitos without the blood sucking proboscis. Adult males can be distinguished from females based on their feather like antennae. After dormancy in the winter, midge flies emerge in the summer ready to lay between 100 and 3,000 eggs per female.

Though midge flies do not suck blood like mosquitos, they disrupt communities in other ways. Swarms annoy both local residents and operators by flying into unsuspecting mouths and flooding outdoor lighting. A study by Selden et al. (2013) found that wastewater operators can develop allergic reactions from midge fly exposure. Chironomids can also cause quite a startle to the public when bright red larvae make their way into drinking water systems.

When it comes to maintaining treatment systems, wastewater operators may be most concerned with the larvae stage of midge flies. Their sticky red bodies cling to suspended solids encasing them in a cocoon of decaying organic matter. Under the protection of these cocoons, they can consume considerable amounts of sludge, bacteria flocc, and nitrifying bacteria. An infestation will cause sludge clumping, rising solids, or foaming issues. In one small town a bloodworm invasion wreaked havoc on an activated sludge plant over a single weekend. The wastewater operator found sticky clumps of eggs had congested the system’s pumps while larvae had eaten away at his mixed liquor suspended solids (MLSS).

Facultative lagoons and secondary clarifiers are a favored breeding ground for these pests. Midge flies prefer to lay their eggs in still, high-nutrient water with fixed media, floating scum, or algae. Once the eggs hatch, larvae will likely sink to the bottom to feed on organic matter and sludge. The hemoglobin that gives bloodworms their red color also allows them to live in low dissolved oxygen (DO) conditions.

To avoid bloodworm infestations, operators should focus on encouraging circulation and limiting food sources. Systems can start midge fly control with mixing, limiting surface scum and algae, installing bug zappers, attracting bats and swallows, or turning off lights at night. Introducing a predatory fish can also help. Lagoon operators can encourage circulation by cutting back overgrown vegetation. Any dead spots in circulation should be addressed. When these methods don’t work, some systems will use larvicides and chemical agents as a last resort. Operators should check that the control methods they’ve selected are approved by their local regulatory authorities before use.

When summer starts make sure your treatment system is kept clean and free of obstructions to circulation. With good preventative maintenance, you can spare yourself the nightmares of a bloodworm invasion.