By Christopher Ingraham
In addition to widespread suffering and devastation, Hurricane Harvey has brought a plague of floating fire ants to the Houston region.
"Floodwaters will not drown fire ants," explains Paul Nester, an extension specialist at Texas A&M, in a pamphlet titled "Flooding and Fire Ants: Protecting Yourself and Your Family." Instead, entire colonies of the aggressive biting insects - eggs, larvae and all - will "emerge from the soil, form a loose ball, float, and flow with the water until they reach a dry area or object they can crawl up on."
For the uninitiated, a fire ant resembles a regular ant in roughly the same way a wolf resembles a golden retriever. They're aggressive, territorial and venomous. Among vulnerable individuals, their stings can be fatal. "Most people hate fire ants without reservation," Florida State University entomologist Walter Tschinkel wrote in a book about the insects in 2006.
Some areas around Houston are reportedly seeing dozens, if not hundreds, of these colonies come ashore in the wake of the flooding there.
Researchers have extensively studied this behavior to find out how, exactly, the ants do it. A 2011 paper by David Hu and colleagues at Georgia Tech found that when you drop a clump of fire ants on a surface of water, they will cling to each other and distribute themselves into a pancake-shaped disc.
The ants can do this because their bodies partially repel water, or, in scientific terms, they are "hydrophobic." When water comes in contact with a fire ant, it beads up into droplets, the same way it does on a car window treated with Rain-X.
"An advantage of being hydrophobic is the ability of ants and semiaquatic insects to trap a plastron layer of air around their bodies, without which they would sink," Hu and his colleagues write. In other words if you try to sink an ant, its hydrophobic body will trap an air bubble with it as it submerges.
These trapped bubbles allow ants at the bottom of their flotillas to survive being partially submerged.
If one ant is mildly hydrophobic, an entire colony of them is even more so. This makes a floating ant flotilla particularly hard to sink, as this video demonstrates: If you push down on a fire ant raft, surface tension pushes the water away with it. (Meanwhile, angry ants will start crawling up the thing you're prodding them with.)
If you somehow succeed in pushing the raft under, the ants will take a massive air bubble down with them.
These properties allow a colony of fire ants to survive on the water for weeks. But that doesn't mean they're invincible. In fact, they have an Achilles' heel: dish soap.
Spray a bit of soapy water on an ant raft and it will break apart and begin sinking almost instantaneously. "As soon as ants become even slightly soapy, they immediately release their grip with each other, which is shown by the disintegration of the raft and its submergence underwater," Hu and his colleagues found.
The soapy water not only makes the ants unable to grab their neighbors, it also prevents the formation of air bubbles around a submerged ant. An experiment conducted in the 1990s found that the application of a mildly soapy solution kills off anywhere from 80 to 90 percent of a floating ant colony within 10 minutes.
Dish soap isn't a large-scale solution for dealing with floating fire ants. "It only spreads so much and it also [has] an effect on helpful organisms like water striders, which eat pests on the water surface," Hu explained in an email.
Spraying an individual floating colony with soapy water also requires getting close to both the water and the ants, which should be avoided at nearly all costs in an extreme flooding situation.