When you live underground, rain and flooding can be a real problem.
Imagine you are one of the 200,000 or so ants living in a fire ant nest. Then imagine it rains for two days, the river floods, and your formerly dry underground network of tunnels and caverns is suddenly underwater.
For fire ants, which are native to the floodplain forests of the Amazon, figuring out how to survive the rise of the big river during the rainy season was critical to their evolution. The trick they came up with was to jump on a life raft and float away, a living raft made up of all the ants in the colony.
This evolutionary tactic has been well known for years. Here in the United States, which has been thoroughly conquered by Brazilian fire ants in the last 80 years, the site of balls of ants floating in flood waters is well documented.
But it was only recently that scientists figured out how the ants do it. The problem facing the ants is that their bodies are heavier than water, which means they sink. How then do tens of thousands of ants manage to cling together and float? Sometimes for months at a time!
The riddle was finally solved a few years ago by a scientist named David Hu at the Georgia Institute of Technology. Working with his colleagues in the Hu Biolocomotion Lab there, Hu threw a bunch of ants in the water, waited for them to ball up, and then froze them with liquid nitrogen.
I interviewed Hu about his discovery a few years ago. At the time, he said that the ants had essentially created a waterproof fabric with their bodies.
“The ants are basically a waterproof surface the world hasn’t seen before … it is a great mechanism to deal with a deluge, one that took millions of years to evolve,” Hu said during that interview. “It is the same principle that Gore-tex works on. It’s highly porous fabric that has lots of air pockets. The water has to do a lot of work to penetrate the fabric.”
Hu found the frozen ants formed the fabric by biting and grabbing onto each other. The fabric formed by their tightly woven bodies helped trap air bubbles, as did the tiny hairs on the ants’ bodies. Those air bubbles helped keep the raft afloat.
They also serve as a life support system for ants on the bottom of the raft, providing air to breathe. Hu’s team filmed various experiments with the ant rafts, including pushing them entirely underwater, where an air bubble formed around the entire pile.
You can read more about Hu’s work here,