At the base of the Alps and Pyrenees mountains are flood plains where, in the right weather, water can cover the ground for days. That's a problem for the Formica selysi ants that make their nests in this area; they have to evacuate their whole colony, saving the queen and larvae by building a raft  with nothing but their bodies. Researchers collected some of these ants and watched them form rafts in the lab. (The video shows a raft being built as water is rising, filmed from underneath.) Queens were placed in the safest place in the center of the raft, but the researchers were surprised to find that the young were put in what seemed like the most vulnerable position at the bottom of the raft. Flotation tests showed that this is actually a great strategy for survival: The bottom of the raft is not a dangerous place for them after all , the team reports today in PLOS ONE. Young ants that were part of a raft survived and later matured at the same rate as young that stayed on dry land. Further experiments showed that the young are more buoyant than adults, which makes them able to support the raft like pontoons on a boat. If the results hold true in the wild, it seems drowning isn't a major problem for the ants; the dangers of rafting are more likely to include being an easier snack for predators like fish.
Video: Ants Build Rafts on the Backs of Their Young