Larvae In Pond Filters / What Are These Worms?

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Larval caddisfly on filter box material

Larval caddisfly on filter box material

The guy:

My name is B___K___ from Cookeville, Tennessee. I attended your talk at Splendor Koi in Marietta Ga, the other month.

I have a question concerning my pond. My pond is about 10,000 gallon with 25-30 fish. Chuck helped me to set up this pond and provided all hardware and filtration.

My question is this spring I have noticed a type of bug that attaches itself to all the filter components, skimmer baskets, skimmer filter racks.

I have several pictures that should help you identify the problem. I would like to hear your recommendations to solve said problem.

My Response:

Hi B____!

Larval caddisfly on filter box material

Larval caddisfly on filter box material

Those are the larval form of some fly, like a caddisfly, or Mayfly. They won’t be a year round thing.
Young koi will eat them on sight.
Hence they should only be in fishless areas e.g. filter boxes, infrastructure.
They’re harmless although certain species can be a liability to fry (very baby fish).
They’re not a symptom of anything.
They need no address or remedy.
If you dislike them, a couple Bream in the filter box will consume them readily.

From the Guy:

Thank you for your response.
The fish are doing fine so it was not an issue to them.
In the filters I also find worm / larva. With a high pressure washer, they get blown off and out of the plastic filters and racks and baskets. Every two to three weeks I take the pressure washer down the creek bed and over the water fall to remove algae. I also use algae-away to reduce the algae propagation.
Again thank you for your response.

B____ K______

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Dr Erik Johnson

Dr Erik Johnson is a Marietta, Georgia Veterinarian with a practice in small animal medicine. He graduated from University of Georgia with his Doctorate in 1991. Dr Johnson is the author of several texts on Koi and Pond Fish Health and Disease as well as numerous articles on dog and cat health topics.