I was admiring another new butterfly that showed up in my backyard last week when this stunning creature landed on a flower right in front of me. I took several pictures and then ran inside to look it up. So now I know this is a Polka Dot Wasp Moth. Its name comes from its coloration which (I suppose) looks like a wasp. Evolutionarily speaking, it must look enough like a wasp to predators or this striking coloration wouldn’t still be part of their phenotype (visible aspects of an organism’s genetic makeup).
The Polka Dot Wasp Moth is actually a moth. You can see the feather-like shape of its antennae in this photo. It also has the characteristic spread out resting wing shape where a butterfly would fold its wings up over its back. Although most moths are nocturnal, the Polka dot wasp moth is diurnal (active during the daytime).
These moths are native to the Caribbean region – from northern South America up through Central America, Mexico, and up into southern Florida. They occasionally make their way further north but are less common and usually don’t survive the winters. The host plant of this species is the Oleander plant which was introduced by the Spanish in the 17th century. The original host plant is thought to be the flowering vine, Echites umbellata Jacq. As the native host plant became increasingly rare, the Polka dot wasp Moth switched over to the Oleander plant as its primary host plant (McAuslane, 1997). Now, this insect is more commonly know in its larval stage as the Oleander caterpillar and is thought of as a pest because of its ability to consume enormous amounts of the ornamental plant.
Both the original host plant and the oleander plant contain highly toxic compounds called cardiac glycosides that the caterpillars ingest and absorb into their tissues where it remains in the adult moth (Raupp, 2015). This toxin makes them inedible to most potential predators – the exception being the predatory stink bug and the red imported fire ant (McAuslane, 1997).
Unlike most moths, the Polka dot wasp moth doesn’t find its mate through pheromones. Instead, the female moth uses ultrasonic sound to attract a mate. The sound is generated by vibrating plates called tymbals on the sides of her thorax (her midsection just behind the head) creating a rhythmic clicking sound that cannot be heard by humans (Raupp, 2015).
Like light, sound exists on a spectrum, some of which humans can perceive and some not. Ultrasound is regular sound (in terms of its physical properties) just with a higher frequency than what humans can hear. Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz. (Wikipedia) This means a sufficiently sensitive recording device should be able to capture ultrasonic sound and the frequency could be slowed down enough for humans to hear it. It wouldn’t be a true auditory experience, but I’ll take some part of the experience over none any day!
So, when I read about the ultrasonic mating calls of the Polka dot wasp, I was curious to see if I could find a recording. I was able to find an image of the sound wave produced by the male and female Polka dot wasp, but no audio recordings.
Then I found this recording featuring the ultrasonic soundscape of the tropical forest slowed down to 1/20th the original speed to make it audible to humans. You’ll hear the ultrasonic singing of several species of katydids and, in the distance, the echolocation call of a bat searching for prey.
McAuslane, Heather. April 1997. Latest revision: September 2016. Latest review January 2020. Featured Creatures: oleander caterpillar, Syntomeida epilais. University of Florida. Publication Number: EENY-9. https://entnemdept.ufl.edu/creatures/orn/oleander_caterpillar.htm Accessed: November 2, 2021.
Ramanujan, Krishna . September 27, 2018. Listen to an ultrasonic forest soundscape. Cornell Chronicle. https://news.cornell.edu/stories/2018/09/listen-ultrasonic-forest-soundscape. Accessed November 5, 2021.
Raupp, Michael J. January 5, 2015. Doubling down on defense: the polka-dot wasp moth, syntomeida epilais. http://bugoftheweek.com/blog/2015/1/5/doubling-down-on-defense-the-polka-dot-wasp-moth-isyntomeida-epilaisi. Accessed: November 2, 2021.
Sanderford, M.V., Conner, W.E. Courtship sounds of the polka-dot wasp moth, Syntomeida epilais . Naturwissenschaften 77, 345–347 (1990). https://doi.org/10.1007/BF01138395
Wikipedia. Ultrasound article; paragraph one. https://en.wikipedia.org/wiki/Ultrasound. Accessed November 5, 2021.