What’s an ant to do when it finds a food item that is too large to carry back to the nest?
Army ants, which forage in groups, will form teams that cart the food item back. Workers of other species will just start dragging the large food item until other workers stumble across the scene and pitch in to help. Or, they may break off a bit of the food, carry it to the nest, return for another piece, and continue that way until help arrives or they’ve finished the job.
Pachycondyla chinensis ants have a different solution. If a P. chinensis worker locates something too big for one ant to deal with, it goes off to find a nestmate — and carries that second ant in its jaws as it returns to the food. Once deposited at the food site, the second ant joins the first in dismantling the item and bringing it back to the nest. Interestingly, the ant being carried remains “totally passive” while in transit.
Researcher Benoit Guenard of North Carolina State University noticed this behavior while observing foraging habits of P. chinensis.
To find out more about how the ants decided whether or not they required help, Mr Guenard placed dead cockroaches in two boxes, or “foraging cells”, close to the nest. One of the cells contained lots of small cockroaches that could be carried individually and the other contained one very large cockroach.
“They quickly learned to bring another worker to the cell that contained the large cockroach,” explained Mr Guenard. “But then we tricked them by switching the cells around.”
Within five minutes, the ants had learned to carry another ant to the correct cell.
This is cool. It also boggles my brain a bit, as I think about how this behavior is encoded. Somewhere in the DNA of P. chinensis, there is a series of instructions that goes something like this:
IF food item is way too big
THEN go find buddy, grab her and bring her back in my jaws
IF buddy grabs me in her jaws
THEN remain perfectly still until I am released at food site
According to Guenard, this buddy-recruiting behavior is something new in the ant research world, unique to this species (that we know of). And that’s precisely why biology is so much fun. Even now, in the age of instant information, it’s still possible to go outside, crawl around on your hands and knees while watching some ants, and learn something completely new to science.
Photo of tandem foraging ants by Benoit Guenard.