What kind of ant is this?

Ive never seen them in my back yard before. I saw what people call a "fire ant", its big and it has an orange/red color to it but then i noticed a few feet away about 50 ants way smaller than it that had abdomens the same color but the rest of their bodies were black. these ones were about the size or normal ants. Any one know what kind of ants these are? thanks :) btw idk what category to put this under so i put it in zoology lol