I've noticed for the past few weeks that near a small fire ant nest near my house there will be a new concentrated "large" pile of dead fire ants every few days. I went and checked out the pile and noticed that one ant in the pile was very slowly moving so I moved it in front of a nearby ant to see if it would take it back to the pile. The ant immediately picked up the slowly moving ant and took it back to the nest, passing right through the dead pile I might add. I'm curious what would invoke this type of behavior among the ants. I'm also curious if fire ants dispose of all of their dead this way.
They do! It's called necrophoresis, and it's a way of keeping infections from spreading. A paper published in 2009 suggest that ants constantly produce "I'm alive" chemicals while they're alive; once they die, the chemical is no longer produced and the ants are carted off.