Is This Caterpillar Trying to Look Like a Velvet Worm?
As many scientists will tell you, despite there being 7 billion of us humans spread to all corners of the globe, we have so much left to explore.
Case in point: Nina Zitani, Ph.D., curator of zoological collections and assistant professor of biology at Western University in Ontario, took a team of graduate and undergraduate students to the Amazonian cloud forests of Ecuador for field courses in 2014 and 2015, and they came back with a double dose of unique, perhaps never-before-seen discoveries.
As reported in the Summer 2018 issue of American Entomologist, while studying the arboreal bryosphere—the thick mosses that grow on trees in the cool, wet, cloudy conditions at elevations above approximately 6,500 feet—Zitani and her students found nine specimens of velvet worms, arthropod relatives so different from most other animals that they’re classified in their own phylum, Onychophora.
Setting onychophorans apart is their “elastohydrodynamic squirt-system,” a mechanism they use to shoot a web of slime at their prey to immobilize them. Velvet worms had previously been documented living in moist soils, mosses, leaf litter, and rotting logs on the ground and in the outer layers of epiphytic tank bromeliads, but their discovery in mosses on living tree trunks constitutes an expansion of their known habitat.
But that’s not all Zitani’s team found. Alongside the velvet worms they found another creature that bore a notable resemblance to the velvet worms but was clearly a caterpillar. After further examination, Zitani and her team have proposed that the caterpillar is a Batesian mimic of the velvet worms—an insect larva that has evolved to look like a velvet worm as a method for scaring off potential predators.
“Co-author Jenna Shulz found the onychophoran and the caterpillar in one of her samples from the cloud forest arboreal bryosphere, and we put the two critters into a white pan for observation,” says Zitani. “They began crawling around and, well—trying not to sound too cliché—my first reaction was ‘OMG get the camera!'”
A velvet worm (lighter in color)—an arthropod-relative so unique that it is classified within its own phylum, Onychophora—and caterpillar of unknown species (darker in color) interact after being found near each other in the Amazonian cloud forest in Ecuador. The caterpillar is proposed to be a Batesian mimic of the velvet worm. Both were discovered by a team of researchers and students from Western University in Ontario and reported in the Summer 2018 issue of American Entomologist. (Video originally published supplementary to Zitani et al, American Entomologist, Summer 2018)
In their report, Zitani and co-authors note the caterpillar’s “pair of prominent tubercles on its head that were similar in size, shape, and surface texture to the antennae of the onychophoran.” The resemblance was hard to miss, Zitani says.
“I found my first onychophoran in the wild in Costa Rica in 1995, and have been interested in them ever since,” she says. “So, at the time of our discovery I was well aware of the conserved morphology within the Onychophora, of the extreme variation in morphology found across the larval (and adult) stages of Lepidoptera, and that onychophorans are, despite their cute appearance, frankly vicious predators. My nearly immediate thought was that the caterpillar could be a Batesian mimic of the onychophoran.”
She and her students documented the specimens but did not have permits to remove them from the habitat, and so as of now both the onychophorans and the potential lepidopteran mimic remain of unknown species, though Zitani speculates the caterpillar may have been of a butterfly species in the family Nymphalidae. She says she hopes to return to region for further research and to identify the caterpillar and velvet worms.
“My favorite part of this project was discovering the novel habitat for Onychophora,” she says. “Another question I have is, how far up the tree trunks do the onychophorans occur? I would like to sample the arboreal bryosphere much higher up on the trees. This gets tricky with the need to transport ladders, et cetera, but of course it can be done. I would also like to know how widespread the onychophoran population is and sample different patches of forest than the ones we have already done.”
The next time around, she’ll take with her a new batch of students, but the ones who went the first time—undergraduates Jenna Shulz, Mitchell Hoyle, and Theodor Steipe and graduate students Yanina Sarquis-Adamson, Yeritza Bohorquez Ruiz, and Andrea Wishart—can vouch for the experience of field work in the Amazon.
“Do not underestimate the value of including undergraduate students in research, nor the value of field courses as experiential learning in science,” Zitani says.