Engineers are grappling with a problem army ants solved ages ago: how can we design massive, coordinated networks that don’t topple when one individual fails? While it seems like big groups need one, centralized commander calling the shots, nature demonstrates otherwise. Simple rules followed by individuals, independently, produce incredible group-level behaviors. An April 2021 study published in PNAS turned to Eciton burchellii, predatory Central American army ants, to learn how they become greater than the sum of their parts. 

E. burchellii hunt in massive swarms, hundreds of thousands of ants strong. When faced with slippery slopes, they team up to form living structures called “scaffolds,” making footholds for the ants coming up behind them.

To model how ant colonies shape their behavior to the environment, researchers traveled to Barro Colorado Island, Panama. They built a moveable platform that could be tilted from 20 degrees (mostly flat) to 90 degrees (completely vertical), set the platform along the ants’ path, and watched. The steeper the slope, the denser the scaffold. Why? Selfish behavior. 

If an ant slips as they're climbing a precarious surface, they will dig in, gripping the underlying surface. Their body acts as a foothold, making the climb less slippery for the rest of the swarm. As more ants slip and catch themselves, their bodies add to the scaffold. As the surface becomes easier to grip, fewer ants slip, and scaffold construction winds down to a halt. This is an example of proportional control, where a system responds in proportion to the amount of error it detects. The rate at which bodies are scaffolded (the system’s response) decreases as fewer ants slip (the error it detects). 

Ants and their remarkable collective behaviors can inspire us to improve our own infrastructure. Mechanisms inspired by E. burchellii scaffold-building, which robustly and quickly respond to change, could be used to design self-healing fabrics, build better traffic control systems, and more.