Slavery was outlawed in 1865 with the Thirteenth Amendment to the United States Constitution, but apparently ants did not get the memo.
ant relishing honey dew from aphid
Ants will often farm (AKA keep them as slaves) and protect aphids. In return for their guard duty the ants relish the honey dew which is excreted by the aphids. The ants stroke the rear of the aphid with its antennae and this causes the honey due to be expelled. This is then eaten and regurgitated in the nest for the developing larvae and queen.
If that is not enough, here is a video for your enjoyment:
to read more go here.
getting older & wiser... 
There is a species of ant here in Arizona that engages in yet another kind of slavery. They raid another species’ colony, steal their young, and then bring them back to their colony to be nurse-ants, provisioning and raising their brood. Crazy, no?