If you refering to fungas gnats they can harm and kill a seedling. An adult plant not so much just a pain in the ass.
However if your referring to Springtails they do not harm the plants typical and eat decaying organic matter in the medium.
This is what springtails look like zoomed up real close
growdiaries.com/diaries/129773-grow-journal-by-m0use/week/740420
growdiaries.com/diaries/129773-grow-journal-by-m0use/week/740420
In any case BTi or some beneficial nematodes should be able to clear that up real fast for yea.
Good Luck & Happy Growing!
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