Because ants are attracted to protein and fructose, "feeding one's ants" means masturbating to the point of ejaculation such that the expelled semen attracts a swarm of ants
Black: "Dude, I've been feeding my ants to Rik's pictures"
Bil: "Why are there ants crawling on my keyboard?"
Mei: "You've been feeding your ants, haven't you? >=\"