HCA: Hermit Crab Association

Hello! I have black fungus nats in my tank. I’ve done a lot of research but I want some personal experience and suggestions. Will they harm my hermit crabs? Do I actually have to dump the sand and add new sand? Will they go away after summer? I have wet food (I know now that it attracts them), moss and coconut fiber. Should I remove this or will they go away eventually?

I don’t know if they’re fungus nats or phorid flies, but when I looked at the forum they look like fungus nats but online phorid flies look the same! They may be a shore fly, I’m so confused.

But they’re all black and round, they can fly

Phorid flies have a prominent hump and will climb and fly around. They tend to go after rotting meat or insects the most, so will be found on wet crab food. Controlling the food source will stop them, given enough time.

Fungus gnats run around the substrate and sort of hop around more than fly. They like the tank because of the wet cocofiber, because their offspring will hatch and live in it. Letting the surface dry out a bit and allowing for air movement will at the very least slow down their numbers. A full substrate change shouldn't be necessary and won't help longterm if they're around to lay more eggs. Some vivarium keepers are using Bt crumbles in the soil for fungus gnats control. This is new with hermit crabs but is likely to be harmless to them, although the Bt bacterium can colonize crustacean digestive tracts and has only been studied in species that live less than two years. Just an option to consider if things get bad.

Neither type of gnat will harm living hermit crabs, though both will consume dead ones on the surface.

Thank you so much! I always see them in my hermit crab food because I put in dehydrated vegetables (which is wet) and they have insects for food. They usually hop and crawl on the surface once I remove the food. Hopefully they’ll go away, they aren’t out of control but they’re annoying. Thank you for the tips!