Rescue attempts by ants were first documented more than 100 years ago. Now Elise Nowbahari at the University of Paris–North and her colleagues report that such efforts are undertaken only for struggling colony mates.
The researchers used a nylon thread to tie a Cataglyphis cursor ant to filter paper, and partially buried the ant under sand. They found that only when active colony-mates were tied to the paper did other ants come to the rescue; chilled, motionless ants, or those of different colonies or species, elicited no aid.
The rescue ants dug sand until they uncovered the snare, which they then bit at. The sophistication of this snare-biting, the researchers add, far outdoes previously reported rescue activities such as sand-digging and leg-pulling, assumed to be responses to chemical alarm calls from any ant.