I recently listened to a talk which I found particularly delightful. Dr. Akito Kawahara from the University of Florida was giving a virtual presentation to the Entomological Society of Washington. He highlighted his research into how moths use sound to defend themselves against bats, and along the way, he also reminded me that insects and plants were interacting with each other LONG before humans were a twinkle in the eye of the cosmos.
Here’s a summary of the facts which I felt were most awe-inspiring:
Moths Have Ears
The evolution of hearing in moths is one topic explored by Akito’s research. The original hypothesis was that moths had evolved hearing in response to pressure from their major predators, bats, who use sound to hunt. However, Akito’s group used fossils and genetic analysis to show that moth ears had actually evolved long before bats did.
Giant leopard moth with wings removed to show ears. Photo credit: Donald W. Hall
Moths Can Scream
In order to jam the sonar signals which allow bats to track prey, moths can make noises of their own. For example, hawk moths can stridulate their genitals extremely quickly and essentially create a wall of ultrasonic noise that confuses any bats hunting them. Tiger moths use a membrane on their thorax to create clicks, and some toxic moths also advertise their distastefulness with specific sounds.
Details of the sound (a) and genital structures (b-d) that hawkmoths use to deter predatory bats. Figure credit: Barber and Kawahara
Moths Create Illusions
Some moths prefer to disappear when bats are chasing them. Giant silk moths have long “tails” on their wings which spin like fans behind them as they fly, scattering sonar signals. These make it hard for bats to tell exactly where they are, and an incorrectly-aimed attack is less likely to be lethal. If you’ve ever tried to produce quality audio for a concert or podcast, you know that soft surfaces absorb sound. Moths use this principle to their advantage and grow soft “fur” all over their bodies. By absorbing any incoming sonar, less signal makes it back to the bat, making it seem like the moth isn’t there at all.
This video by Boise State researchers shows a bat aiming at the long "tails" of an African moon moth, then a luna moth. The bat manages to rip the tails off, but the moths, which can fly without them, skirt away to safety. Video credit: Jesse Barber Lab.
Moths are older than dinosaurs
The latest estimate puts moths at 300 million years old. In case you’re counting, this means moths were flying around for 50 million years before dinosaurs showed up. Even more bizarrely, the earliest moths had chewing mouthparts. A nectar-sucking proboscis (which is the standard now) wouldn’t have done moths any good before flowering plants existed! Butterflies, which are a subset of moths, appeared on the scene relatively recently, around 100 million years ago. They are primarily active during the day, which is another tactic for avoiding hungry bats.
A sphinx moth unfurls its proboscis to drink nectar from a flower. Photo credit: IronChris, CC BY-SA 3.0, via Wikimedia Commons
what about Moths in human-dominated landscapes?
Earlier this year, our lab published a review on how urbanization might change insect behaviors. Research has shown that human use of artificial light at night impacts many animals, including moths. Considering how critical sound is to their anti-predator defensive behaviors, moths are likely impacted by human-created noise as well. Until we know for sure, it is recommended that we all do our best to limit light and sound pollution at night. Akito published an article titled “Eight simple actions that individuals can take to save insects from global declines” which is definitely worth a read if you care about protecting our wondrous moths.
Kelsey McGurrin, lab manager
P.S. the Burghardt lab space at UMD was previously occupied by Dr. Charlie Mitter, Akito’s PhD advisor. Small world! (For humans, at least. We’ve been on earth less than half a million years.)