Ancient Parasitic Wasps Ate Their Victims From the Inside Out

Scientists probing more than 1,500 ancient fossilized fly pupae have discovered four species of wasp that used these growing insects as a home for their own babies.

Sophisticated scans of the fossils, which hail from the Paleogene some 66 to 23 million years ago, revealed numerous invading wasps encased inside fly pupae. The creatures would have sapped nutrients from the growing flies as they developed inside their hosts.

When maggots develop into flies, they swaddle themselves in a cocoon-like bundle. Safe inside, their bodies develop from tiny little worms to complex winged creatures. This developmental phase is called the pupal stage.

Eventually they emerge from their pupal case as adult flies, just like a butterfly emerges from a chrysalis. But in 55 of the cases examined by scientists writing in the journal Nature Communications, invading wasps got in the way. Female wasps, researchers think, pierced the pupae and laid eggs inside, leaving baby wasps to develop and feed off their fly hosts.

Imaging revealed the ancient smuggled cargo in stunning detail. Although the pupae are only around the size of a grain of rice, you can clearly see the developing wasps down to the hairs on their bodies.

Researchers named the four newly-discovered species Xenomorphia resurrecta, Xenomorphia handschini, Coptera anka and Palaeortona quercyensis.

If you're a movie buff, some of these might sound familiar. Xenomorph is the name of the bloodthirsty creatures that hunt terraforming space explorers in the Alien films. Squid-like face-suckers lay Xenomorph offspring inside live human hosts. The baby aliens gestate as parasites until they outgrow their puny hosts and rip their way out through their victims' chests.

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X-ray imaging reveals concealed parasitoid wasps inside mineralized fly pupae. The image shows the photograph of a 30-40 million year old fly puparium and a digital section of the same specimen, revealing a wasp, which developed at the expense of the host fly. Georg Oleschinski/Thomas van de Kamp

It's incredibly rare to find a fossilized parasite still embedded inside its host, so researchers didn't think they would find such a large haul. "We didn't really expect to find these parasites inside," study author Thomas van de Kamp of the Karlsruhe Institute of Technology in Germany, told National Geographic. He grew impatient when the first few fossils proved fruitless, "I was already a little bit bored," he told the publication.

But the tenth fossil sample revealed a stowaway wasp. "It was absolutely clear," he said. "It really looked me into the eye through the screen."

Researchers hope the sophisticated imaging tech used to unveil these smuggled creatures will help uncover other hidden secrets whilst preserving the integrity of ancient fossils.