Four new species of wasp from the Palaeogene (around 66 to 23 million years ago) of France provide direct evidence of ancient parasitic events. The findings are published in Nature Communications this week.

Evidence for parasitism in fossils is generally rare as it requires preserved information of the interaction between both partners. As a consequence, the fossil record of parasitoid wasps is nearly exclusively restricted to isolated adults, with few examples of unidentified larvae trapped in amber next to their hosts. The only record of a putative fossil parasitoid wasp inside its preserved host comes from a thin section of a mineralized fly pupa from the Quercy region in France from approximately 40 to 30 million years ago.

Thomas van de Kamp and colleagues used high-throughput synchrotron X-ray microtomography to examine 1,510 fossilised fly pupae from the Palaeogene of France and identified 55 parasitization events by four newly discovered wasp species. The newly described species - Xenomorphia resurrecta, X. handschini, Coptera anka and Palaeortona quercyensis - all developed as solitary parasites inside their hosts and exhibit different morphological adaptations for exploiting the same hosts in one habitat. For example, the authors note that C. anka and P. quercyensis display modifications to their antennae, wings and petiole (the narrow 'waist' that separates the abdomen from the thorax), which make them better equipped for a ground-dwelling lifestyle compared to the two Xenomorphia species.