Booger Beetles and Fecal Shields
Entomologist Dr. Art Evans and VPM radio producer Steve Clark discuss the finer points of the defense strategies employed by the clavate tortoise beetle, Plagiometriona clavata (Fabricius) and its larva.
Steve Clark: I'm Steve Clark with Dr. Art Evans, entomologist, and this is What’s Bugging You. How is it that we're coming to talk about boogers today?
Art Evans: [laughing] This is public radio. Well, as you know, people approach me with identification questions, and my wife Paula and I were walking down the street one evening and my good friend and neighbor, Marshall, pulls up beside us and says, “Hey, I've got something you need to look at.” And he was very serious, which is totally unlike him. And he says, “It looks like a booger.” [laughing] And I thought, okay, and nothing is coming to mind, absolutely nothing. And I'm thinking, “What does this have to do with me?” It doesn't even sound like an insect. So I assured him that we would swing by the house on our way home and take a look. One of his friends had taken a photograph of a beetle they had found on a screen or something like that. And I recognize it right away. It was the clavate tortoise beetle. I can see why he called it what he did. It looks like a little crusty, clear and dark blob. In its native surroundings, it would be on a leaf.
Clark: If an oyster were black, that's what it would kind of look like.
Evans: Yeah, it has kind of a shiny, soupy . . . It looks like anything but a beetle, which I think is how it defends itself. It has this dark central pattern, and then the sides of it are what we call explanate. They're very thin and wide and translucent, so it has a very unusual appearance. And if you look at it from the side, it's cone shaped and it has sort of a peak over the top of it. The larvae are even more fascinating, I think, because they protect themselves with a fecal shield.
Clark: What is that? Evans: I'm so glad you asked. [laughing] Instead of disposing of their waste material, they save it on an anal fork, and then they hold it over their body as a protective shield, and presumably it makes them less appetizing because it might have chemicals in it to discourage predators. And it makes them less visually apparent as well. They don't look like a beetle larva. They just look like a pile of stuff. These beetles belong to a group of beetles known as tortoise beetles, because they're sort of tortoise-shaped. They have a very uniform outline, and they tend to be sort of convex. Some of them are smooth, some of them are spiny, some of them have translucent windows, and many of these species do protect themselves as larvae with very intricate fan-like shields that are made up of cast exoskeletons, previous larval instars and/or bits of fecal material.
Clark: How widespread are they?
Evans: Tortoise beetles are found worldwide. You have species that are only known from the New World, species that are indigenous to the Old World. Here in the New World, they're primarily tropical, but we have several different species here in the East, and some of them have the ability to change their colors too. There's one that's on morning glories that's brilliant gold, but they have the ability to shift fluids in the layers of their exoskeleton, and suddenly they'll turn dark brown.
Clark: Another fascinating story from the world of entomology.
Evans: You bet.
Clark: From Dr. Art Evans, he’s a research associate at the Virginia Museum of Natural History. You’ll find photos, audio, and links to the museum and Art’s Facebook page at vpm.org/bugs.
Dr. Arthur V. Evans teams up with VPM Radio producer Steve Clark for a weekly feature, “What’s Bugging You?,” which airs during NPR’s Morning Edition. The program takes its name from another of Evans’ books “What’s Bugging You – A Fond Look at the Animals We Love to Hate.”
Tune in each Tuesday at 8:45 a.m. or at 5:44 p.m. on VPM News.