The crypt-keeper wasp’s manipulation of its host and exit through its head was first described in the literature in 2017. But as scientists have studied it further, things have only gotten weirder.

It started when Scott Egan, an evolutionary biologist at Rice University who first described the crypt-keeper, began collaborating with Andrew Forbes, an ecologist at the University of Iowa.

Between 2015 and 2018, Dr. Forbes’s lab had collected more than 23,000 galls from oak trees in Iowa, the Midwest, New England, North Carolina and Texas. His team had hoped to learn about the diversity of gall wasp species and find galls that had been parasitized. But the more he talked with Dr. Egan, the more they suspected that the crypt-keeper was using multiple host species — unusual behavior among parasites, which are usually very specialized.

Dr. Forbes’ lab confirmed the hunch by rearing some wasps and their gall crypts in plastic cups within a chamber that simulated changing seasons. The parasitoid crypt-keepers did have many different species of hosts, and all the hosts had one key thing in common: the galls they occupied were small, smooth, non-woody, lacking fuzz or sharp spines — defenseless. These little crypts were perfect for Euderus’ keeping.