News > January 22, 2004

By Justin Stevens

Contributing Reporter

William Conner, a professor of biology, and graduate student Nickolay Hristov have made some groundbreaking discoveries about communication between bats and moths.

When bats are hunting, they send out high-pitched squeaks, which bounce off of objects and help the bat locate its prey. In response to these so-called echolocation pulses, certain types of moths emit a clicking sound back to the bat.

There has been much speculation in the science world as to the purpose of the moth’s clicking. One theory suggests that the moths are attempting to startle the predator long enough to evade it. Another says the moths are trying to disrupt the echolocation process with the clicking, much like submarines that stay hidden by jamming sonar.

Conner and Hristov, however, have gathered new evidence that suggests a third theory: the moths may be speaking to the bats.

Their work has not been published yet, but it is slowly wrapping up. “It’s extremely exciting,” Conner said. “We’ve been at this for six years.”

Conner’s theory was a derivative of the work of Kenneth Roeder, who in the 1950s and ’60s produced a lot of what we now know about moths and the evolution they went through to develop ears.

Each moth ear consists of a single neuron, compared to tens of thousands in humans. Studies have shown that moth ears are particularly adept at hearing a certain frequency, between 35 and 40 kHz. This is the exact frequency of a bat’s echolocation cry. Biologists deduced that these ears that moths had developed were, essentially, bat detectors.

The work that Conner and Hristov have done focuses on a certain species of moth known as Arctiidae, or tiger moths. These insects are very brightly colored and often poisonous to predators, like bats. What was most interesting to Conner was that they had developed tymbals on either side of their thorax, which made little clicking sounds every time they detected being hit by bat sonar.

From this premise, Conner theorized that the tiger moths were actually sending a message to the bats telling them not to eat the tiger moths because they were poisonous.

In their lab at the university, Conner and Hristov began conducting experiments to try to prove this communication theory, which is known as aposemitism. The experiment that they designed used four types of tiger moths that either made the clicking sound or did not and that were either poisonous or not. They cultivated bats in the lab that had never tasted tiger moths and then observed how they learned to adapt when tiger moths were suddenly thrust into their environment.

Before the experiments began, the scientists made up several graphs that predicted how the bats would react based on aposemitism, jamming and the startle theory.

It was immediately evident that the other two theories would not hold. If the moths were trying to jam the signal, one would expect that moths that click, even without poison, would not get eaten as much. However, as Conner observed, “They ate them up like popcorn.”

The experiment is performed over a period of seven days. The resulting graphs consistently match up with the predicted graph the scientists had made for aposemitism. This proved that the moths were in fact communicating with the bats.

Such behavioral studies of the animal kingdom can have many practical uses. The study of predators and prey that use sonar detection could lead to new stealth devices capable of avoiding sonar detection. The chemical aspect of the studies could lead to new pharmacological capabilities and the discovery of new medicines.

For Conner, however, the goals are much simpler. “I want to know the answer to this evolutionary puzzle,” he says. “That’s what drives me.”

That puzzle continues to unfold. The new discoveries that Conner has made from Roeder’s research are already generating another interesting idea. Now that the moths have developed the ability to communicate with bats, they may be using their new ears and tymbals to talk to each other.

Moths have been documented using the clicking sound as a mating call and they are not alone. Many insects, including beetles and preying mantises, have been found to have ears for detecting bats.

One day we may find that this tool developed for survival has evolved into a language of the insect world.