Fungus gnat larvae are supposedly wormy things up to 1/4" long. I had them through several grows, although I never actually saw the larvae, just the adults flying around the top of the pots. My seedling survival rate got very low, like 1/3 or 2/5. They'd sprout and then rot before the cotyledon could open, or if they survived they wouldn't start to grow 'til the 2nd or 3rd week above ground. I hope I have them under control now, with mosquito bits and yellow sticky cards, a break between grows, new intake filter, and new coco on the next grow.