Before These Parasitic Wasps Finished Devouring Live Flies, They Became Fossils

https://www.nytimes.com/2018/08/28/science/wasps-parasites-fossils.html

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Wasps are the horror-flick killers of the insect world. Sure, their stingers are scary, but it’s their parasitizing practices that really send a shiver down the exoskeleton.

“They are insects that eat other insects alive,” said Lars Krogmann, an entomologist at the State Museum of Natural History Stuttgart in Germany. “They don’t just kill them, they want to keep them alive for as long as possible.”

Known as parasitoid wasps, these types of wasps are much smaller than the yellow jackets that make people panicky at picnics. With needlelike ovipositors, parasitoid wasps lay their eggs into or on top of other insects. As the young wasps grow, they devour their hosts and eventually kill them, sometimes by bursting through their abdomens like in the movie “Alien.”

Nearly every insect species has at least one species of parasitoid wasp that specializes at murdering it. The emerald cockroach wasp, for example, injects a mind-controlling cocktail into a cockroach’s brain that turns it into a zombie and host for its eggs. Spiders too can fall victim to a hungry wasp larva that forces it to weave webs to protect its cocoon. There are even parasitoid wasps that lay eggs in other parasitoid wasps.

Now, scientists have found direct, concrete evidence, published Tuesday in Nature Communications, that these insects have honed their grisly tactics over the course of millions of years. Using synchrotron X-ray imaging, researchers from Germany found parasitic wasps lurking inside more than 50 fossils of developing flies that were 30 million to 40 million-year-old.

“It’s the first time we definitely have proof of a developing parasitoid wasp inside its host in the fossil record,” said Thomas van de Kamp, an entomologist from the Karlsruhe Institute of Technology in Germany and lead author. Researchers previously had uncovered ancient parasitoid wasps entombed in amber, but most were without their hosts.

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Dr. van de Kamp, Dr. Krogmann and their colleagues made the discovery while re-examining a collection of immature flies that fossilized during their pupa phase, which is a cocoon-like period that occurs between the larval and adult phases.

The pupae fossils measure only 3 or 4 millimeters long and resemble grains of rice, but are as hard as stone. Most were found in the 1890s and early 1900s in southwestern France. In the 1940s, a Swiss entomologist named Eduard Handschin studied and described many of the fossils, after which they remained relatively forgotten.

At first Dr. van de Kamp examined 29 ancient fly pupae using the X-ray imager, which “unwrapped” the fossils in front of the scientists in real time. The first nine were empty, just stones. But the tenth was special.

“I was getting bored. It was like ‘O.K., stone. Another stone. O.K., another stone.’ And then it was ‘Wow!’” said Dr. van de Kamp. “It was immediately clear there was a wasp inside.”

The find prompted him and his colleagues to re-examine more museum samples. Over the course of a week they took images of more than 1,500 fossilized fly pupae and found 55 with parasitoid wasps.

Dr. van de Kamp surmised what happened about 30 million years ago when an animal died and its rotting carcass attracted the flies. Inside the decomposing flesh, the flies laid their eggs. The eggs hatched and became larvae that feasted on the dead remains. The maggots began their pupal phase in hopes of leaving as flies.

Enter the wasps.

The insects most likely laid their own eggs inside the pupae, disrupting the fly’s development. As the wasp larvae ingested the pupae, they grew into adult wasps. Then at some point before the adult wasps had the chance to emerge, they died and the entire thing — host and parasitoid — was fossilized.

The team identified from the specimens four newly discovered wasp species. Two of the species, Xenomorphia resurrecta and Xenomorphia handschini, they named after the gut-busting Xenomorphs in “Aliens.” Fitting for creatures so frightening.