JUNE
2011

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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06-09-11

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Surf's Up, Insect Style


red fire ants stacked on each other and floating in water
Fire ant raft
photo credit: David Hu and Nathan Milot

To some people the cry, "Surf's up" means heading to the beach with a surfboard in tow. The thought of big waves breaking on the shore reminds most of us landlubbers of songs by the Beach Boys or even "California Dreaming" by The Mamas and The Papas.

Ocean beaches might be attractive destinations for vacationers, sunbathers and surfers but not insects. Only about 300 of the approximately 2 million described species of insects live around seawater. This is true even though people who visit the seashore sometimes conclude that insect numbers are very high there. That is because many of the insects that live near the sea are species that bite. To make matters worse these biters - mosquitoes, horse flies, deer flies, and midges - sometimes have high population numbers.

Neither saltwater nor freshwater are commonly used by insects as a habitat. About 3 percent of all insect species are aquatic in any life stage. That means that most insect species don't live in water, salt or otherwise, at any time in their life. A few such as dragonflies and damselflies do and because of that we call them aquatic insects. So what happens to all of those non-aquatic insects when they encounter water? It depends on circumstances. All insects need water to survive, normally in food such as plants, but an excess of free water generally is not a good thing.
 
So what happens to insects when the land floods? A lot of insects drown, that's what. A Johnny Cash song, "Five Feet High and Rising," includes the following lines:
"Well, the hives are gone, I've lost my bees
The chickens are sleepin' in the willow trees"

When floods inundate the land the animals that can avoid the water by running or flying have a good chance to survive. But animals that can't run or fly often become flood victims.

A few animals, including some insects, survive flood conditions by emulating human surfers. These creatures hitch a ride on floating debris, such as sticks or living plant material.

The overall champion of the flood survivor competition for the insect world has to be that notorious pest the fire ant. All ants are social insects, and most species live as a colony located in a nest in the soil. As you might imagine, underground colonies of ants are susceptible to being wiped out by prolonged floods. However, fire ants exhibit a behavior that allows a colony to survive floods. They use their bodies to create a floating raft of ants.

People who live in fire ant country have often witnessed these ant rafts floating on the water during floods. But no one knew exactly how the process worked until a couple of engineering professors and a graduate student at Georgia Institute of Technology decided to research the process.

Here's what they found. When submersed in water, groups of the ants link their feet together to form a ball. Because of air trapped by tiny hairs on the bodies of the ants, the insects can breathe, and the group of ants becomes buoyant. Once on the surface of the water the ants rearrange themselves into roughly a two-layer raft. This is the floating structure of ants so familiar to people in fire-ant country.

Individual ants don't want to be in the underwater portion of the raft anymore than surfboarders want to be hanging onto their board while underwater. So the ants are continually rotating their position from the bottom to top of the raft. Because of the air trapped near the ant's body, the individuals located underwater can still breathe.

Ants are social insects; therefore, the survival of individuals is meaningless. It is the colony that must survive. So when a fire ant nest is threatened by flooding, the worker ants gather up eggs, pupae, and the queen and head to the surface of the ground where they are prepared to form a living raft. The assemblage allows the ants to survive for many days. When the waters subside the six-legged flood-farers can again establish a nest underground.

Fire ants heed the call of waters rising. Surfboarders respond to the call, "Surf's up!" In both cases, it's a chance to ride the waves. One for survival, the other for fun!

 

Writer: Tom Turpin
Editor: Olivia Maddox