first of all, they don't seem to spawn at night
ph's seem to be any of the bats...
so you are all alone? or noone else is killing in the area? fine, tag and train all the bats you see to the little helpful guards at the wall...
sit and med up and tag the wasps that spawn, eventually you will get your wing(s) for the bug collection quest. it seems fairly rare. keep training the bats til you get your drop(s)