They're weird looking, they're tiny, and they're blood-red - or at least a creamy pink color. What are they? They're non-biting midge fly larvae, also known as bloodworms. Though they're an unsettling infestation to see in your filter, they're actually a sign that your pond is happy and balanced.
What's in a Name
Midge flies hail from the family Chironomidae, which includes more than 10,000 different species worldwide. Some varieties appear bright red in color thanks to a hemoglobin-type substance that helps them live with oxygen-depleted water, giving them their "bloodworm" nickname.
As adults, midge flies resemble mosquitoes, but they have fluffy antennae and no blood-sucking proboscis. Large numbers of them can be a nuisance as their droppings can cause damage to paint, brick and other surfaces. And when their tiny corpses pile up, they can cause a stink.
Feasting in Your Filter
These insects thrive in freshwater aquatic and semi-aquatic environments. In their larval stages, they live in tree holes, plants, rotting vegetation, soil and artificial containers - including filtration systems, infesting Media Pads where there's an abundance of organics from debris and fish waste. They spend their time attached to the container's solid surface and eat as food floats by.
Midge flies lay their eggs in water, preferring it to be still, clear, dark and safe from critters like fish and frogs that nosh on the larvae when they emerge. To protect themselves, the bloodworms actually create and live in tiny half-inch tubes they build from mud, algae and other naturally occurring resources. Look closely in your filter, and you'll probably see some of these worm-sized mud huts.
A Tasty Fish Treat
Don't worry: These little guys won't harm your pond or your fish. In fact, if one wriggles its way into your pond, it will be a welcome treat for your fish. Goldfish and other smaller fish will gobble them and their little mud homes; koi and other larger fish will treat them as tasty hors d'oeuvres.
Bloodworms are quite nutritious for fish. In fact, the insects are about 55 percent protein - which is a key nutrient fish need to grow and reproduce. So rather than balk at the tiny worms, scoop them out of your filter and give them to your pond dwellers. They'll thank you for them!
Last Updated: February 2, 2023