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Fire ant life’s expert in USF

Researcher Deby Cassill says ants and humans have a lot in common.
Dr. Deby Cassill has spent 30 years researching the lives of fire ants.
Dr. Deby Cassill has spent 30 years researching the lives of fire ants. [ CLIFF MCBRIDE | Photo: Courtesy University of South Florida ]
Published Jul. 24

Times Correspondent

Dr. Deby Cassill, an associate professor in the Department of Integrative Biology at the University of South Florida, describes her main research as “the origin of altruistic behavior among individuals across the animal kingdom.’' She is best known for her 30 years of research into the behavior of fire ant colonies, where thousands of sterile female workers guard the nest, fight the enemies, forage, feed the queen and fertile offspring and take care of the young.

“I feel that academia is such a privileged career,’' said Cassill, 74, noting that she gets “to work with students in a field that I love, explore and never be bored.’'

She talked with the Tampa Bay Times about the lives of ants.

Ants and humans have the same hormones in their brains?

They do. It’s a surprising finding that all animals with a nervous system have nerve cells that communicate in the same language, and that it has been conserved, that language with which nerve cells talk to each other. And it’s all chemical – melatonin, serotonin, oxytocin, dopamine, these are some of the more familiar hormones. …

But all animals, evolving from about 450 million years ago, have nerve cells that communicate with the same language with minor variations. It’s been conserved because it’s essential for animals to be able to find food, avoid becoming food and find a mate and care for young.

You showed a film of a queen in labor and being very gentle with the offspring.

It’s stunning to me that there are contractions. The egg doesn’t just pop out. It takes a couple of minutes sometimes. … She then lifts it up with her forelegs. She has little opposable thumbs on her forelegs that are different than her middle or hind legs. She’s able to rotate the egg, licking it, and carries it over to where the other eggs are. And she guards it. I’m doing a study on newly-mated queens because they are likely full of oxytocin. … What it does, it’s the love hormone, that sense of well-being and calmness and adoration for something that is now apart from your own body.

Some ants work harder than others?

I put 20 of them in a small home. Over a six-hour period, I filmed them and I gave them four jobs to do. What turned out with those 20 ants – and I replicated this several times – is that about 10 percent, so two out of the 20, would do all four jobs that I gave them at very high rates. And I called them workaholics. And then another two at the bottom did very little to nothing, kind of hung out with the family, the sisters. … And the other ants would maybe take one or two of the four jobs and do that very well but not the others.

You’ve studied ant abdomen-wagging. Why do they do this?

My goal right from the beginning was to look at ants at a human scale, meaning up close and videotaped, so that I could see individuals, maybe five individuals at high magnification. It looked like little people. And with these videos, I would ask a question, set up an experiment: (I’d) give them food of low quality sugar water, like 3 percent sugar water, 10 percent sugar water, 25 percent sugar water, which is like a really sweet lemonade, and filmed them to discover who went to get what and how they communicated information about the quality of sugar back in the nest with the other workers.

And I noticed this wagging, it’s like a tail wag on a dog, and couldn’t find any work on it. … What we found was…they waggled like crazy when they ingested food and when they were caring for the brood. … Until somebody comes up with an alternate explanation, my interpretation is that it was just a show of pleasure, recognizing a family member or really good food.

Ants can chirp, like crickets do?

Ants have those same stridulations on the back of their thorax, the middle section segment, and have a little pointed thorn-like protrusion at the beginning of their abdomen. And if they move it down, it’s a “prrrrrrt,’' which we could hear with a stethoscope. And it is emitted by ants that are buried when the nest is damaged by another animal, anteater or cow stepping on it. And the ants above, on the surface, will actually start digging and rescue their sister.

What is flagging?

Flagging is when the back legs are reared way up in the air; it’s moving their abdomen straight up at a 90-degree angle from the ground. The stinger is out and there’s a droplet of venom. They’re not injecting it in anyone yet, but they have detected a stranger. ... Usually, and this is fascinating, usually it’s another fire ant family. And they have territories and they cross each other and find each other at the edge of their territory and they then immediately start shaking the droplet to communicate, and they have many different types of oils that they can produce and eject out the stinger. ... It’s such a dramatic change of posture that the ants around them can see it and they can smell because they are atomizing the alarm chemical. ... And that’s an indicator to start looking around for an enemy.

In battle between colonies, some ants play dead, then get up and run when the danger is over?

When they are newly hatched, their jaws are weak, their stingers are weak, and they’re easily killed.

So here is what we observed. ... If the ant played dead and did not move, the invading ant would stand over it, tap it with the antennae and keep a leg on it and sniff around to see if there were any other ants, but would not bite or inject venom as long as the focal ant didn’t move. … And it would lay there as long as the other ant was watching over it. But within a minute, sometimes less, the other ant’s like, okay, it’s not moving. It’s dead. I don’t want to shoot it, waste my bullets and my venom on it. So I’m going to move on and find somebody else to fight.

It’s exactly what we do. We’ll kick an enemy. We may shoot it… to make sure they’re dead. But we don’t want to waste ammunition in a war on something that appears to be dead.