Bats eat moths

Moths scream: I am poisonous!

Many insects use warning colors to convey the message: Don't eat me, because I'm poisonous. But of course this is useless against bats - the hunters of the night only rely on their hearing. Therefore, some species of moth have also developed a warning cry, researchers report.

Some insects, fish or the famous poison dart frogs have nothing in mind with camouflage; instead, they use the opposite strategy: their striking colors and patterns are intended to make it clear to potential predators that an attack is not worthwhile, because I am poisonous. Aposematism is the technical term for this widespread strategy in the animal kingdom.

The group of so-called tiger moths (Arctiinae) also use this concept - many species are colorful and striking. When eating, your caterpillars ingest toxins from plants, which they make inedible even as adult moths. During the day they convey this to birds and mammals through the warning colors, but these visual signals are useless against the nocturnal attacks by bats. Because these predators only use ultrasound for orientation and to catch prey.

Warning message conveyed twice

It was already known that tiger moths have a special organ with which they can generate ultrasound sounds themselves: Through extremely fast muscle contractions, these so-called tympanic organs are deformed in such a way that this sound effect occurs. Researchers at Wake Forest University in Winston-Salem have now for the first time documented through studies on wild moths and bats that the sounds represent a form of acoustic aposematism: They deter bats.

For their study, they examined the tiger moth species Pygarctia roseicapitis and Cisthene martini in connection with hunting bats. In some of the insects, the researchers blocked the tympanic organs so that they could no longer make sounds. It turned out that mute moths were attacked by bats almost twice as often as those who made sounds. Evaluations of camera recordings of the nightly actions also showed that the bats actively avoid “screaming” moths. This makes it clear: the tone replaces the message of the color during the day at night.

According to the researchers, the concept is a clever alternative to the elaborate evasive maneuvers that many other moth species perform when bats attack. Shouting “I'm toxic” may be more energy efficient, say the biologists.

Source: Wake Forest University

© - Martin Vieweg
17th May 2016