New Species of Parasitic Wasps Found Inside Fossilized Fly Cocoons

parasitoid wasps
Of the 1,510 fly pupae scientists X-rayed, 55 were found to contain well-preserved parasitoid wasps, including four new species. Nature Communications

Scientists named a fossilized wasp after Xenomorph XX121 — the vicious creature lieutenant Ripley battles from the 1979 movie "Alien." And like that fictional killer, this actual (albeit prehistoric) insect reproduced in a way squeamish people might find disgusting — but it worked.

In 1944, Eduard Handschin, a Swedish insect scientist, wrote a paper describing hundreds and hundreds of odd, oval-shaped stones that had been found by some French phosphorite miners five decades earlier. Capsule-like in appearance, each specimen was roughly 3 millimeters (0.1 inches) long.


Radiometric dating showed that they were between 34 and 40 million years old. The curiosities eventually found a home at the Natural History Museum of Basel, Switzerland.

Handschin recognized that they were the fossilized pupae of prehistoric flies. A pupa is like a housefly cocoon; it's a hard case in which squirming maggots transform into adult flies. But sometimes, a rather unfortunate thing interrupts the metamorphosis.

While Handschin was studying his pupal fossils, he cut a few of them up into thin slices. One cross-section revealed an eye-catching blot inside a pupal fly's abdomen area. Handschin thought — but couldn't prove — that this smudge was the body of a parasitic wasp.

Around 50 percent of all extant animals are regarded as parasites by scientists. It's one of the most common lifestyles on the planet, and it comes in many forms. An especially unsettling group of parasitic organisms are the "parasitoids" — insects whose larvae develop inside a host that they eventually kill. Delightful.

Parasitoid wasps make up 10 to 20 percent of the world's living insect species. Given their modern success, there's no reason to doubt that they were also a big component of many prehistoric ecosystems. Since parasites rarely fossilize however, scientists don't know much about their evolutionary pasts.

Now we've learned that a motherlode of parasite fossils was staring us in the face this whole time. On Aug. 28, 2018, Nature Communications published a new study about the pupa remains that Handschin looked over back in the 1940s. Led by insect expert Thomas van de Kamp, an international research team X-ray scanned 1,510 prehistoric fly pupae. (Some were being housed at the Basel museum, others resided in the Swedish Museum of Natural History.)

This was a huge collaborative undertaking, one that required biologists, paleontologists, physicists, computer scientists and mathematicians to join forces. But boy did it pay off. Of the 1,510 pupae they looked at, 55 were found to contain well-preserved parasitoid wasps.

Unfolded wings and intact antennae were clearly visible on several of the parasites. The degree of preservation was so good that van de Kamp and his colleagues were able to identify four new species of long-extinct wasp on the basis of these specimens.

"The most numerous species we named 'Xenomorphia ressurecta,'" van de Kamp explains in a blog post. "The genus name refers to the Xenomorph creature of the 'Alien' media franchise, which was discovered in old eggs and also develops as a parasitoid (at the expense of an unfortunate human host, though)." Hey, all the best science fiction leans on scientific fact.