Imagine that you're driving along a country lane. As often happens, the road suddenly transforms from a well-paved street to a pothole-ridden nightmare. As your suspension and your stomachs start to tire, your friends in the back suddenly force you to stop the car.
To your amazement, they jump out and lie across the potholes, beckoning you to drive your car over them. It may seem like a far-fetched scenario, but if you were an army ant, such selfless behaviour would be a matter of course.
Army ants are some of the deadliest hunters of South America. Amassing in legions of over 200,000 ants, they become a massive predatory super-organism that fan out across the jungle floor leaving dismembered prey in their wake.
Behind the killing front, the corpses of the ant's prey are taken back to the nest by foragers. But the route back home is not a smooth one. At an ant's size, small twigs and leaves can be the equivalent of a bumpy, unpaved motorway.
Scott Powell and Nigel Franks from the University of Bristol found that at least one species of army ant (Eciton burchellii) solves this problem with living paving. Certain workers stretch their bodies over gaps in the forest floor, allowing their food-carrying sisters to march over them.
The ants carefully size-match to the holes that they plug. Powell and Franks stuck planks with different sizes of hole in the path of the ant column, and found perfect matches between ant and hole.
By smoothing the trail home, they ensure that other workers can return food to the colony as fast as possible. Powell and Franks calculated that this increase speed means that the colony as a whole gets more to eat, even thought the plugging ants cannot carry any food themselves.
It may seem that the plugging ants have a hard lot in life. But they are ultimately rewarded for their temporary sacrifices. When the foraging trip finally ends, the pluggers can look forward to a hearty meal when they return home. By taking on a specialised role, these ants improve the performance of the colony as a whole.
Reference: Powell & Franks. 2007. How a few help all: living pothole plugs speed prey delivery in the army ant Eciton burchellii. Animal Behaviour doi:10.1016/j.anbehav.2006.11.005