One ancient type of wasp appears to have had an especially freaky way to trap prey 99 million years ago. It used a mouth-like structure on its backside, fossils now suggest.
“When you look at the head, the thorax and the wings, [this wasp] looks quite normal,” says Lars Vilhelmsen. But its abdomen is very different, the insect biologist points out.
Most stinging wasps, such as yellow jackets, have rounded abdomens that end in a point. The ancient wasp’s totally unique abdomen instead has flaps that lay on top of each other. He likens it to a plant — the Venus flytrap.
Vilhelmsen’s team shared its findings March 27 in BMC Biology.
“It’s significant and amazing,” he says, “that we can find something that looks like nothing that we see today.” Vilhelmsen works at the Natural History Museum of Denmark. It’s part of the University of Copenhagen.
Amber-jacketed surprise
Along with researchers at Capital Normal University in Beijing, China, Vilhelmsen examined 16 wasp fossils. All had been unearthed from a valley in northern Myanmar (a Southeast Asian country also known as Burma).
At first, Vilhelmsen couldn’t believe it. He thought an air bubble trapped in the amber might have caused the wasps’ abdomens to look so weird. But the amber in which they were encased had helped preserve their anatomy. And CT scans would confirm the abdomen truly was bizarre.
Entomologist Anderson Lepeco, too, was shocked when he first saw pictures of these wasps. “I’ve never seen something like that,” he says. Lepeco, who was did not take part in the study, works at the University of São Paulo in Brazil.
For a second, Lepeco thought the first wasp that he saw was deformed. But when all had the same anatomy, he became convinced that this species “was a really, really cool bug.”
Named for a monster
The scientists named the wasp S. charybdis (Kur-IB-duss) after a sea monster in Greek mythology. Why? The wasp’s abdomen reminded them of the mouth full of teeth depicted in some drawings of Charybdis.
The wasp’s abdomen is split into three flaps — an upper, middle and lower one. In a few fossils, the lower flap gaped far from the other two. In other specimens, the lower flap pressed tightly against the middle and upper ones. Because of this difference in position, the team thinks the flaps could grasp things.
The lower flap also had several thin hairs poking out of it. These hairs would likely trigger the flaps to shut when a critter brushed against them, the team suspects. That’s much like how the hairs on Venus-flytrap leaves trigger these leaves to snap shut, locking in a meal.
Predators usually trap prey. When a praying mantis catches its dinner, for instance, the prey is so close to its mouth it can dine quickly. But this wasp’s weird abdomen is far from its mouth. It is much closer to the insect’s egg-laying organ.
For that reason, the scientists suspect these wasps might have wielded their back-end traps to restrain other creatures so that they could lay eggs on or inside of them.
“I think it’s the most likely explanation,” agrees Lepeco. Parasitoids are insects that lay their eggs on or in other animals, he notes — and “all the insects in [this wasp’s] group are parasitoids.” When a parasitoid’s babies hatch, they’ll feed on the animals that are carrying them.
Lepeco studies a group of insects that use stingers to inject a paralyzing venom into their prey. Afterward, they lay their eggs on this victim. Lepeco suggests the newly discovered ancient wasps might have laid their eggs on other creatures to feed their hatchlings.
Scott Shaw is an entomologist at the University of Wyoming in Laramie. He agrees with Lepeco that the most likely reason for the weird abdomen was to restrain insects. He, too, believes the wasps likely laid their eggs on their hosts, rather than inside of them. But, he adds, clearly “no one has observed the behavior” in the now long-extinct wasp. So scientists can’t be certain of this.
Still, the mere existence of this feature is remarkable, says Lepeco. Like dinosaurs and saber-toothed tigers, insects of the past were very special, he says. “We forget that at the same time those species were alive, there were also insects — and the insects were also cool.”