HA HA HA I had same problem, they only hung out 1 or 2 plants for some reason, and seemed to like congregating in 1 of the trays that the pot sat in
I firstly, sat in my grow room like kerate kid, cathing em mid air then humanley eiliminating them out of existence
Then plan 2, i got a normal household lighter, and tinkered with it, until it became a flame thrower, then bust into my room when there are not expecting it, and fuk up there little meeting in the tray.
Put it this way i won in the end, i think there may arround 3 clever ones left. I'll get em tho!
Show no mercy, as the ones you spare, will regenerate that little swarm in no time!
Good luck