The Parasite That Compels Other Parasites to Shove Their Heads Into Holes, and then eats them

Ed Yong in The Atlantic:

In 2015, Scott Egan was walking along a Florida beach when he noticed some oak trees with distinctive swellings on their branches. He recognized them as the work of gall wasps—parasitic insects that lay their eggs in plants. From within, the larvae manipulate trees into creating chambers full of nutritious tissues. Tucked away in these crypts, the young wasps can eat their fill in safety. Once they turn into adults, they chew their way out and fly away.

Egan, being a keen naturalist and an expert on gall wasps, snipped off some of the branches, took them back to his lab, and kept them in a container on his desk. After a couple of months, he noticed that a few orange insects had fallen to the bottom. Those were the gall wasps—an orange species called Basettia pallida, which had finally chewed their way out of their crypts. But not all of them made it. Egan noticed that some were stuck, their heads wedged in their own escape holes.

To find out why, Egan teamed up with Kelly Weinersmith, a parasitologist and a colleague at Rice University. They cut open the branches and realized that every stuck wasp had a companion inside its crypt—a second wasp, half the size of the first, and iridescent blue. And in every case, the blue wasp was eating the orange one.

More here.