Leaves being eaten

I notice this on a regular and everytime I try and find these little pesky buggers I cant I must turn over almost every fan to find nothing its so strange but I think i know whats happening. IF you have cold air intake you maybe pulling in flys or odd little critters with your air. now most of these are not going to harm your plant they have a little nibble then die out as there are no partners to mate with in your grow room. I mean flowering plants will always attract wasps and bees as they have evolutionary senses that help them find pollenating plants I have noticed a could of wasps in my tent in the summer time and I dont kill them they just die cause they cant get out. Hope this helps if you think its something more serious then checking the underside of fan leaves is the best best and also the main stems.