This Ancient Wasp Might’ve Used Its Butt Flaps To Trap Prey

FLORA LICHTMAN: This is Science Friday. I’m Flora Lichtman.

Entomologists report a new fossil find, a prehistoric wasp that had one of a kind attack method. It seemed to grab its prey with its butt flaps, capturing its booty in its booty like a tuchus flytrap. And then once the wasp had its prey in tail, it injected its parasitic eggs into it, which would then hatch and slowly devour the victim from the inside out.

Here to tell us more is Lars Vilhelmsen, curator at the Natural History Museum of Denmark in Copenhagen. Welcome to Science Friday, Lars.

LARS VILHELMSEN: Thank you very much.

FLORA LICHTMAN: Give us a character sketch of this wasp. When did it live?

LARS VILHELMSEN: Yeah, it’s a 100-million-year-old wasp from the Cretaceous at the same time as we had dinosaurs still living on the Earth. It’s well preserved in amber. It’s from what is known as Myanmar amber.

FLORA LICHTMAN: Myanmar amber?

LARS VILHELMSEN: Yeah so it was probably living in a forest area. And, in fact, we found 16 specimens of this very particular wasp, so we were able to study its anatomy in greater detail than we would normally be able to.

FLORA LICHTMAN: Would you agree with my assessment that it captured prey in its butt flaps?

LARS VILHELMSEN: That’s what we write in the paper, so that’s how we imagine that this could have happened.

FLORA LICHTMAN: I’m certain didn’t use the term butt flaps in the paper.

LARS VILHELMSEN: No, we’re talking about abdominal flaps, sixth and seventh segment of the abdomen of the wasp.

FLORA LICHTMAN: And how do they seem to work? Are they triggered mechanically? How do they actually trap a victim?

LARS VILHELMSEN: Yeah, we imagine that this wasp was– it doesn’t seem to have been able to move very fast. The legs are not very long. And so we imagine it would probably wait like an ambush with the trap open. And on the edge of the lower flap of the trap, there’s very elongated hairs extending fan-like, and we imagine these served as trigger hairs.

FLORA LICHTMAN: And this is how a Venus fly trap works, the trigger hairs.

LARS VILHELMSEN: Yeah, yeah, more or less. The Venus fly trap, the trigger hair sits inside the flaps, so the fly or whatever the plant has to catch has to move all the way in between the leaves. That might not have been necessary for the host of this wasp. So when a potential victim or host moved just behind the abdomen of the wasp, the wasp could sense it and then quickly lunge backwards and grasp the host in the flaps.

FLORA LICHTMAN: You wrote in the paper that this apparatus is unlike anything previously reported in any insect known to us.

LARS VILHELMSEN: None of us have seen anything like it before. At first when we saw this, we thought it must be some kind of artifact, some kind of deformation of the specimen, which is not uncommon.

FLORA LICHTMAN: Oh, you didn’t even think it was real?

LARS VILHELMSEN: No, not at first glance. And as far as we know, you can never know for certain what an extinct organism lived like, how it used its anatomical features to go around its daily life. So what you do, you compare with organisms living today, and the further back we go in time, the more weird insect life becomes and the further we have to look for modern parallels. In this case, we had to go outside the animal kingdom to find something that we thought resembled what we were looking at.

FLORA LICHTMAN: Do you think that insects get overlooked? If you found a dinosaur that used its butt to capture prey, I feel like it would be headline news?

LARS VILHELMSEN: For sure. And this is– it’s very unusual for me to have a paper getting so much attention. This has never happened to me before. So I certainly feel that insects are overlooked in general, but they basically invented everything that humans could think of and usually millions of years before humans.

They have invented agriculture. You have leafcutter ants doing that, and, yeah, almost everything you could think of.

FLORA LICHTMAN: What’s this wasp’s name so we know what to call it in our nightmares?

LARS VILHELMSEN: Yeah, it’s Sirenobethylus charybdis. This is a fancy name, of course. Charybdis refers to a monster in ancient Greek mythology which almost swallowed Odysseus when he was traveling the world. And, yeah, Sirenobethylus was– a siren was also a monster that lured sailors to their death. But it’s also because there’s a group of mammals, sea cows and manatees, and the tail of a manatee in outline actually looks like the flap of this wasp also. So that was another reason to name this species like this.

FLORA LICHTMAN: I love it. Thank you, Lars.

LARS VILHELMSEN: You’re welcome. Thank you.

FLORA LICHTMAN: Lars Vilhelmsen, curator at the Natural History Museum of Denmark in Copenhagen.

Copyright © 2025 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/