Tiny Black Worms in a Fountain: Midge or Caddisfly Larvae?

Quarter-inch, triangular-headed worms darting on fountain rocks when the pump is off? They're almost certainly insect larvae—harmless outdoors, but you may not want the adults indoors.

Likely Identifications

• Midge larvae (Chironomidae): Usually smaller (⅛–¼ inch), red or clear, no cases. Very common in still water.
• Caddisfly larvae (Trichoptera): Build portable cases from sand, plant bits, or silk. ¼–½ inch. Case-building behavior is a giveaway.

Are They Harmful?

No. Both are beneficial—filter feeders that clean water and feed fish. They indicate decent water quality.

Winterizing Concern

If you bring the fountain inside, larvae may pupate and emerge as flying adults (midges swarm; caddisflies are attracted to lights). Most will have pupated by late fall in temperate zones.

What to Do

• Leave them: If fountain stays outside, they're part of the ecosystem.
• Remove before moving in: Drain, scrub rocks, rinse plants. Or keep fountain in an unheated garage.
• ID confirmation: Photo helps. Check fishpondinfo.com/bugs.htm for more pond invertebrates.

Enjoy the biodiversity—it means your little fountain is a functioning habitat.