Fungus gnats are a common pest in pet isopod, millipede, other invertebrate, reptile, and amphibian enclosures. Fungus gnats are generally not harmful, but can be annoying,,and can sometimes cause problems. Here are so,e tips, based on my experiences, that can help you control fungus gnats.
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These gasket-sealed locking bins can help keep fungus gnats out: https://amzn.to/2WUHH2R
They are not enough to do the job on their own, however:
Fly ribbons will effectively trap fungus gnats, without pesticides: https://amzn.to/3bEzhC8
These cards are another type of fungus gnats trap: https://amzn.to/2WVXChp
Mosquito bits are a bacteria-based biological control of fungus gnats: https://amzn.to/2AphZvz