Ant nests have great undertaker capacity. Workers detect the dead and haul them outside to a pile of debris and corpses, often within an hour after death. Here a worker carries a young ant in the pupal stage to the refuse pile.

When an ant dies, other ants move the dead insect out of the nest. Sometimes, the dead ant gets moved away very soon — within an hour of dying. This behavior is interesting to scientists, who wonder how ants know for sure — and so soon — that another ant is dead.

One scientist recently came up with a way to explain this ant behavior. Dong-Hwan Choe is a biologist, a scientist who studies living things, at the University of California, Riverside. Choe found that Argentine ants have a chemical on the outside of their bodies that signals to other ants, “I’m dead — take me away.”

But there’s a twist to Choe’s discovery. These ants are a little bit like zombies. Choe says that the living ants — not just the dead ones — have this death chemical. In other words, while an ant crawls around, perhaps in a picnic or home, it’s telling other ants that it’s dead.

What keeps ants from hauling away the living dead? Choe has an answer for that question, too. He found that Argentine ants have two additional chemicals on their bodies, and these tell nearby ants something like, “Wait — I’m not dead yet.”

So Choe’s research turned up two sets of chemical signals in ants: one says, “I’m dead,” the other set says, “I’m not dead yet.”

Other scientists have tried to figure out how ants know when another ant is dead. If an ant is knocked unconscious, for example, other ants leave it alone until it wakes up. That means ants know that unmoving ants can still be alive. Many scientists, like Choe, think there must be a chemical on a dead ant’s body.

Choe suspects that when an Argentine ant dies, the chemical that says “Wait — I’m not dead yet” quickly goes away. Once that chemical is gone, only the one that says “I’m dead” is left. When other ants detect the “dead” chemical without the “not dead yet” chemical, they haul away the body. This idea — that some chemicals fade away — was Choe’s hypothesis, or idea to test, for his experiment.

To test his hypothesis, Choe and his team put different chemicals on Argentine ant pupae. A pupa is the stage of an ant’s life just before it becomes an adult. When the scientists used the “I’m dead” chemical, other ants quickly hauled the treated pupae away. When the scientists used the “Wait — I’m not dead yet” chemicals, other ants left the treated pupae alone. Choe believes this behavior shows that the “not dead yet” chemicals override the “dead” chemical when picked up by adult ants. And that when an ant dies, the “not dead yet” chemicals fade away. Other nearby ants then detect the remaining “dead” chemical and remove the body from the nest.

Understanding this behavior may help scientists figure out how to stop Argentine ants from invading new places and causing problems. Choe would like to find a way to use the newly discovered chemicals to spread ant killer to Argentine ant nests.

The ants’ removal behavior is important to the overall health of the nest. Their behavior is not so different from ours: When a human dies, the body is usually buried or cremated within a few days.

“Being able to quickly remove dead individuals and other possible sources of [disease] … is extremely important for all animals living in societies, including us,” says Patrizia d’Ettorre of the University of Copenhagen. “Think about all the effort and money that we invest daily in waste management.”

Power words: (from Yahoo! Kids Dictionary)

Hypothesis: A tentative explanation for an observation, phenomenon or scientific problem that can be tested by further investigation.

Chemical: A substance with a distinct molecular composition that is produced by or used in a chemical process.

Going Deeper:

Researchers have now found that microbes living under the ocean floor appear to produce propane and another gas called ethane. These microbes chew up ancient organic material, such as leaves and twigs buried in the sand, and they generate the gases as waste products.

That’s a surprise. Scientists had thought that propane and ethane could be produced only in the same way that petroleum is—by great heat applied to ancient, buried material.

Kai-Uwe Hinrichs examines a sample taken from a cylinder of sediment drilled out of the ocean floor.

Ocean Drilling Program Leg 201 Science Party

A team led by Kai-Uwe Hinrichs of the University of Bremen in Germany went on a research ship equipped with an enormous drill that dug out cylinders of sand or rock thousands of feet long. When the researchers examined these cylinders, they found traces of ethane and propane locked in the sediment.

Normally, to generate these gases, Earth’s heat cooks organic material in sand for many thousands of years. This can happen only at spots above cracks in Earth’s crust, where heat can leak out from inside Earth, and where thick layers of sediment would act like a blanket.

But the samples that Hinrichs and his coworkers had looked at contained thin layers of sediment. Some cylinders had also been obtained from places far from any cracks in Earth’s crust. So where could the gases be coming from?

Scientists already knew that microbes could break down organic material to produce a related, simpler gas called methane. So, undersea microbes were the only thing that made sense.

“When you can’t come up with any geologic source, then biology is an obvious candidate,” Hinrichs says.

The finding may someday lead to practical applications. Propane is valuable as a fuel, and ethane is used to make plastics. Pulling propane and ethane out of sediment is too difficult to be practical. But if scientists can better understand how microbes create the gases, they might be able to use the microbes’ methods to make ethane and propane directly from organic material.—J. Rehmeyer

Going Deeper:

Rehmeyer, Julie. 2006. Gassy bugs: Microbes may produce propane under the sea. Science News 170(Sept. 30):213. Available at http://www.sciencenews.org/articles/20060930/fob4.asp .

You can learn more about propane at en.wikipedia.org/wiki/Propane and ethane at en.wikipedia.org/wiki/Ethane (Wikipedia).

Cutraro, Jennifer. 2006. Microbes at the gas pump. Science News for Kids (April 12). Available at http://www.sciencenewsforkids.org/articles/20060412/Feature1.asp .

Sohn, Emily. 2006. Plant gas. Science News for Kids (Jan. 18). Available at http://www.sciencenewsforkids.org/articles/20060118/Note2.asp .

______. 2004. Drilling deep for fuel. Science News for Kids (Sept. 29). Available at http://www.sciencenewsforkids.org/articles/20040929/Note3.asp .

ScienceFairZone
Harvesting Biogas from Manure
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20050504/ScienceFairZone.asp