This should go without saying - BUT I'm going to say it anyway.
Make sure that your formula container is closed all the way. I was making DD a bottle yesterday morning and noticed two ants in there. I guess DH didn't close it well enough and ants got in. I threw it out along with her cereal.
**We have the sugar container not far from the formula container. I guess some sugar spilled and attracted the ants**
Re: Ants in formula