Army ant bodies are designed to stick to each other. Scoop up an individual worker and you’ll often find yourself pulling away a string of dozens. Army ants are clingy creatures, they adhere to each other as though magnetized.
All ants have little hooks on their feet, the tarsal claws, but those of army ants are especially large. These hooks allow individuals to link together.
This talent for self-engineering is especially useful for the nomadic army ant lifestyle. When the time comes to encamp, they can string together living curtains of ants in a matter of minutes. Army ant bivouacs are made from the ants themselves, a vibrant structure that protects the vulnerable brood and maintains temperature within a single degree of optimal.
But ants don’t link together just for bivouacs. They also make living bridges to smooth their foraging trails.
Myrmecologist Scott Powell- who occasionally contributes to Myrmecos Blog- recently studied the logistics of trail-smoothing. The gains are not trivial. Scott performed a set of experiments varying the substrate characteristics and estimated that the amount of prey funneled back to the bivouac as a result of the smoother surfaces was greater than had those same hole-plugging ants been engaged in prey retrieval. In other words, the colony gets more food when some workers abandon foraging for road work.
Scott also worked out how an ant decides to fill a hole (assess hole size and amount of ant traffic), and how it decides to move on (no traffic for 5 seconds). Perhaps if we’re lucky, he will drop by and tell us more.
- Franks, N. R. (1989). Thermoregulation in army ant bivouacs. Physiological Entomology 14: 397-404.
- Powell, S., Franks, N. R. (2007). How a few help all: Living pothole plugs speed prey-delivery in the army ant Eciton burchellii. Animal Behaviour, 73: 1067-1076.