i also killed them when young, before i learn Buddhism.
ants are said to be the most stubborn of all. u kill them they
still reborn as ants. so the karma of them hating u is not as much
as human do. ants are too ignorant.
intention also important. if don't know like u boil water or
driving or walking will accidentally kill a lot of small creatures.
just keep a non-hatred heart/mind. and be mindful. recite Amituofo.
wish they all reborn in higher realms. then the karma is
transformed positively.
/\
I young use brain I put sweet in cup to tempt them come
then pour water drown them.
I killed countless. My childhood mates also. We even compete who
kill more.