Some 35 million years ago in what is now France, hundreds of maggots munched their way through decaying corpses. When they had had their fill, each one wrapped itself into a tight little bundle and waited to transform into a fly.

Then along came the parasitic wasps.

Now, in a rare example of a fossil found inside a fossil, researchers have unveiled the stunningly preserved remains of 55 ancient fly pupae that house parasitic wasp invaders. Using advanced technology to peer inside the rice-size fossils without damaging them, the team created images of the wasps in breathtaking detail—down to their fragile wings and the hairs on their backs.

The haul includes four wasp species that were previously unknown to science. And while