I Have a Question

Yesterday when I was giving exam at exam hall. I saw many red ants there.
Here in our India commonly there are two type of ants found
1. Red
2. Black
I have always notice that red ant always bite everyone and has very slow speed when they walk or run.
But on the other hand black ants doesn't bite and they run very fast as compare to red ants.
My question is why they both are different from each-other?