Science: Living bridges

A very interesting group of ants are the army ants. Instead of having a colony like most ants, army ants are nomadic. They basically set up camp, called a bivouac, of which the ‘tent sail’ consists of living ants. From there, they conduct raids every day on the surroundings. Once they practically wiped out much of the life in the surroundings, they migrate to a new place and set up camp again. Rinse and repeat.

Eciton burchelli bivouac. You can see the surface of the 'camp' consists of living ants

Eciton burchellii bivouac. You can see the surface of the ‘camp’ consists of living ants. Picture by Alex Wild (www.alexanderwild.com)

While raiding, they will make a big highway, kill everything in its path, and bring it back to the camp. These highways are on the forest floor. This means they are not nicely paved, but contain a lot of holes and irregularities. Furthermore, many many many ants walk over these highways at the same time. However, it would greatly reduce efficiency (and thus the food intake of the colony) if the ants had to wait in a traffic jam.

Eciton burchelli 'highway'. Note the soldier on the right that stands guard

Eciton burchellii ‘highway’. Note the soldier on the right that stands guard. Picture by Alex Wild (www.alexanderwild.com)

Scott Powell and Nigel Franks found an interesting way in how these ants solve this problem. Once an individual finds a hole in the highway, she will assess how big the hole is. If the hole is the right size for her body, she will plug the hole with her own body. This enables other individuals to just run fast over the highway, instead of slowly navigating over the holes.

Here you can see how the ants plug holes in the experiment of Powell and Franks

Here you can see how the ants plug holes in the experiment of Powell and Franks. Copyright Animal Behaviour (Elsevier)

In this way, the ants ensure that they can catch and bring back as much prey as possible in the time they have, and thus ensure a faster growth of the colony!

Source:
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

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