Acoustic Aposematism: How Tiger Moths Produce Warning Signals to Deter Bats

For million years, moths have been subjected to tremendous hunts by echolocating, insectivorous bats. Due to this, moths have undergone series of selective evolution in order to survive the harsh environment.

While birds and other mammals use visual aposematism signals, such as bright and highly contrasting patterns, to warn their predators of their toxicity, moths can utilize such method in surviving their battle against bats, which hunts during the night. In order to cope up with echolocating bats, moths developed an acoustic warning signal to deter the bats.

According to a new study published in the journal PLOS ONE, tiger moths have the ability to produce ultrasonic signals to warn bats that they don't taste good. These signals are produced by the moth's tymbal organs which have the ability to answer bat echolocation cries with high-intensity, broadband clicks.

Early observations and laboratory experiments have suggested that the tymbal sounds of some species can serve an acoustic aposematic signal, advertising the presence of noxious chemicals sequestered in the larval stages.

In addition to the aposematic function of the tymbal sounds, previous studies also suggests that aposematic clicks could serve a sonar jamming or weakly jamming function.

"This means that in evolutionary history these moths first evolved these sounds for use in warning bats of their toxicity and then sometime later, these sounds grew in complexity in certain species to perform a sonar jamming function," said Nick Dowdy, a biology graduate student at Wake Forest University and co-author of the study, in a statement.

In order to better understand the mechanisms behind the behavior and its efficacy, the researchers observed two types of tiger moths, the Pygarctia roseicapitis and the Cisthene martini, using multiple infrared cameras to reconstruct bat-moth interactions in three-dimensional (3-D) space.

After analyzing the collected data, researchers found out that tiger moths with intact tymbals were 1.8 and 1.6 times less likely to be captured by bats relative to those rendered silent. They also discovered that C.martini has employed lesser evasive flight, solely relying to aposematic sound production to avoid predation.

These findings imply that certain species may have evolved to rely on their warning sounds instead of the evasive maneuvers common to most eared moths.