Small Red Worms in Ponds & Filters (Info & Removal)

Whether you’re an existing or prospective pond owner, at some point you’ll likely come across tiny bright red or reddish-pink worms in your pond, and particularly in your filters when you clean them. They’re commonly known as bloodworms, and are the aquatic larvae of non-biting midge flies. As larvae, their blood is rich in hemoglobin, lending to their distinct, and sometimes alarming, blood-red coloring.

These kind of midge flies are commonly found in Europe, South America, Africa, and North America. The adults lay their eggs on the surface of freshwater habitats, such as your pond, and upon hatching the larvae will attach themselves to solid surfaces within the water (chiefly on the undersides of rocks and inside of your filters). 

They usually construct tiny tubes to encase themselves for protection from predators out of mud and small bits of sediment and algae, and feed on any minuscule bits of food matter that float by – this is why they find filters particularly appealing, since an easily accessible feast of food matter is sucked into the filters from the pond!

Are Bloodworms Good or Bad for Ponds?

Overall, these little guys aren’t bad for your pond. In fact, most fish, birds, and frogs will gladly eat them, and can be used to supplement their diets since bloodworms have a high iron content and are over 50% protein. In addition, the larvae can also aid in cleaning the water by consuming excess nutrients and algae that would otherwise diminish the water quality.

However, midge fly adults often die in large masses and can form a thick, unappealing layer over your pond that will also contribute to waste. You’ll need to use a skimmer or net to remove the dead adults and prevent oxygen depletion in the water as they decompose, but they can simply be set aside to be eaten by birds, raccoons, voles, and plenty of other opportunistic terrestrial critters looking to pack on the pounds during the plentiful summer months.

If you have too many bloodworms, they can reduce your filter’s effectiveness so be sure to check your filters frequently during the warmer months and scrape off the bloodworms if there appears to be a large number of them. You can then either feed them to your fish, move them to the underside of some rocks in your pond (if you don’t mind having a few bloodworms around), or place them in moist soil.

Bloodworm Life Cycle – How Long Do They Live?

As young bloodworms continue to develop, they’ll enter a pupal stage for a few days, then swim out of the water and inhabit terrestrial locations such as tree holes and soil, eventually becoming adult midge flies. These look quite similar to mosquitos, but don’t actually bite. There are other species of midges that do bite, though the varieties – known as Chironomidae or commonly called non-biting midges or lake midges – that produce bloodworm larvae do not – which is lucky for us!

Afterwards, in a span of about three days, the adult midge fly will mate, lay eggs, and then die. From egg to larva (bloodworm) to pupa to adult, the lifespan of a non-biting midge fly is typically anywhere from 10 days to about a month, though larvae that hatch in late autumn are sometimes able to overwinter in their protective mud shells until the following spring. The bloodworm portion of the life-cycle lasts at least a week, and sometimes several weeks if they are not able to obtain enough food to fuel an efficient metamorphosis into adulthood.

1) Manual Removal Methods

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Bloodworms can be removed simply by scraping them off of your filters and rocks (and cleaning your filters more regularly in general), using an aquatic vacuum to remove both eggs and larvae from the bottom of the pond, and a skimmer to remove any that are floating about in the water itself.

To keep adult populations in check and thereby reduce the number of eggs and larvae in your pond, place a couple of bug zapper lights around your property (away from your pond so as to not attract them to the water). You’ll need to clean these light traps out, though, to prevent them from shorting out or malfunctioning due to a buildup of dead midge flies.

2) Biological Control Methods (Natural)

Another useful, natural method is to incorporate more fish into your pond that will eat the bloodworms (bottom feeders such as catfish and koi work best), as well as planting floating and marginal aquatic plants within and along the shore of your pond that will attract dragonflies, damselflies, frogs, and birds that enjoy eating both the larvae and adults. What other fish eat bloodworms? Quite a few, actually! Check here for a full list of fish that eat all different types of pond larvae, including bloodworms and mosquitoes.

If the above methods aren’t working to your liking, multiple larvicides exist that will specifically target aquatic insect larvae, such as mosquitos and midge flies. Currently, the only EPA approved larvicide explicitly for midge flies in the United States is Aquabac Xt – and it doesn’t harm the rest of your pond.

This purely biological, natural larvicide contains a bacteria called Bacillus thuringiensis israelensis that the bloodworms are unable to digest. When consumed by the larvae, the bacteria form a thick protein crystal that kills the bloodworms soon after ingestion.

If you’re unable to get hold of Aquabac Xt, you can also find the same bacteria strain, although in lower concentration, products designed for mosquito larvae, such as mosquito dunks and bits. Although intended for a different kind of larvae, the products contain the same active bacteria ingredient, so should be just as effective against bloodworms. They’re also 100% natural and safe for use in fish ponds!

3) Chemical Control Methods (Licensed Use Only)

Alternatively, there are also larvicides available that utilize chemicals as well as bacteria to increase the efficiency of the treatment. However, they are also have the potential to be very harmful to the environment, your fish, and your overall water quality. As such, try using the natural methods listed above first, as controlling with bacteria-based products would be a safer option, especially for fish ponds.

If natural methods do not produce the desired results, look into insect growth regulator larvicides such as Altosid that will kill adult midge flies, and organophosphate insecticides (the latter can only be applied by a licensed professional in much of the United States, as these insecticides also damage other aquatic organisms).