Mini Ants are very week and will not attack you but if you step on it or hit an ant, it will attack you and it will call for help. Any other ants within 32 blocks will respond to this call and will attack you too.
There is a flag that you can change using config file that turns on the ant ability of take the item that you are holding when it attacks you. This will happens randomly, but when it happens, the ant will run away from you very fast with your item.
 

Care should be taken:

When an ant find an item on the floor, it will pick the item and run away. Five seconds after this, a new ant will spawn at the location where the first ant found the item. Every time an ant picks an item, a new ant will spawn at that location. In a few seconds you will see a lot of ants carrying items from on side to another and you can't do anything about this because if you try to kill one of them, a lot of ants will attack you and this is very bad.
 

Destructive Ant:

There are special ants and "special" in this case is not a good thing....
Normal ants can carry items that they found over the floor but Destructive ants can harvest blocks to carry and this means that your house is not a safe place!

Don't forget that ants can climb walls and they are very very fast!!