r/BatFacts • u/remotectrl 🦇 • Jun 25 '22

The adult form of the woolly bear caterpillar, the isabella tiger mother (Pyrrharctia isabella), produces sounds to discourage bat predation. Video

https://youtu.be/EXgio0fBdgM
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u/remotectrl 🦇 Jun 25 '22

As we currently understand it, there are 3 major reasons tiger moths produce sound. The first is to warn predators that they are chemically defended (also the subject of a future journal entry); we call this "acoustic aposematism" in the biz. The second reason is to mimic the warning signals of other tiger moth species; we call this "acoustic mimicry", and often the mimics can be dishonest cheaters looking to present themselves as being more dangerous than they really are to bats or birds (or curious biologists). The third reason is to disrupt the echolocation signals of bats; we call this "sonar jamming", but this requires a certain level of complexity in the moth sounds. The acoustic characteristics which generate a "sonar-jamming effect" are currently a hot topic of investigation in my work and the work of other researchers. An additional complication is that all three of these functions could be working at the same time; we say these are "non-mutually exclusive functions".

Pyrrharctia isabella is one of the many tiger moth species which produce sound. They click in response to physical restraint and in response to bat echolocation. You would never know this by grabbing one of these moths from your sheets and listening. Why? Because even the lowest pitch they produce is well above 20,000 Hz, the oft-cited frequency threshold for humans. At 29 years old, my hearing threshold is only 16,500 Hz, so typically humans do much worse than 20,000 Hz. Instead of listening for the sounds, you can look for the physical action of the sound-producing organ; we call this organ the "tymbal". I'll have a special post about this in a future journal entry.

And they produce a lot of sound! I won't go into the details of how we quantify these signals (maybe another journal entry?), but I personally believe that the woolly bear is capable of jamming the echolocation of its bat predators. That's a big deal because that behavior has really only been confirmed for one tiger moth species, Bertholdia trigona. I'm currently investigating this possibility in conjunction with other researchers. Your contributions to this project are really important to push this work forward!

From The Woolly Bear Project

2

u/natureboy-sickflair Jun 26 '22

Appreciate this!!! Cool post, thank you!

1

u/ElizaIsEpic Jun 26 '22

Fascinating!! I actually gasped when I heard it!