Offloading Ant Rafts

Fire ants

Fire ant raft
Photo: PNAS

How do fire ants in a raft transition from floating on water to walking on dry land? Fire ants don’t wait until the water sinks to the level of the land. Leaves, branches and tree roots often dangle into the water forming a bridge from the water to dry land. Upon a raft colliding with a bridge, the workers on the bottom that are facing the bridge will grasp the bridge and anchor the raft. Workers riding atop the raft are the first to leave the raft and explore the bridge and the dry land. Workers identify a suitable site for a nest and lay pheromone trail between the raft and the site. Over a period of hours, ants leave the raft and congregate at the new nest site.

Ants in the raft that have more than 2 links to other ants or the bridge do not disengage. The ants on the outside with two or fewer links are the ones that disengage and walk atop the raft to the bridge. This behavior unloads the raft from the side opposite the bridge and maintains the link between raft and bridge.

A queen will only leave the raft after a suitable number of workers have established on dry land. The queen is the most valuable ant on a raft. By leaving the raft in the middle of the process, a queen will always be surrounded by defenders. The last individuals to leave are those that are connected directly to the bridge.

This orderly process, governed by simple behaviors of the individual ants, ensures the safe relocation of the queen and the maximum number of workers.

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
This entry was posted in behavior, by jjneal. Bookmark the permalink.

One Response to Offloading Ant Rafts

  1. Pingback: Offloading Ant Rafts | Entomo Planet

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