Why is my cat eating ants? And will it hurt him?

Just today, I was walking into my kitchen and found my cat hunched over, licking the floor. When I looked closer, I saw a sparse line of moving black dots. I picked up my cat (because he was really going crazy about eating the ants), and was about to put down some ant powder when I realized that my cat might end up eating the poison if it was stocked with dead ants. Also, if I let my cat eat the ants, will the problem go away?