Every year, Scott Egan and his students crisscross the country looking for odd, round things called galls that grow on plants. They are, essentially, plant tumors. Once you start looking, they’re everywhere. Egan stops at county parks, cemeteries, church parking lots, even the side of the road. It was on one of these trips, to Florida, that they picked up a gall unlike any Egan had seen in 15 years of studying plant tumors.
Well, actually, he didn’t even realize it at the time. When a student brought him the unusual-looking gall—it had a vine wrapped around it—Egan dismissed it as a seed or fruit of the vine. Luckily, someone had the presence of mind to investigate further. They broke it apart and at the center was a single adult wasp, dead and mummified.
To Egan, an evolutionary biologist at Rice University and a connoisseur of galls, the wasp itself was not that surprising—at least once he accepted that the pea-sized brown nodule truly was a gall. Such tumors are often caused by parasitic wasps called, appropriately, gall wasps. They lay eggs inside of plants. Once hatched, the larva tricks the plant into growing a swollen, nutrient-rich gall, providing itself with food and shelter. Once it’s taken and taken and taken from the plant, the fully grown wasp bores out of the gall and begins its adult life.
What really intrigued Egan was the vine attached to the gall. The Florida oak trees where his team found this unusual gall were covered in a yellow tangle of love vine, a parasitic plant. Love vines send their suction-cup roots all over the oak, sucking out nutrients. These poor Florida oaks were being doubly parasitized—by the gall wasps and the love vine at the same time. When the two parasites met, something weird happened. The love vine hijacked the gall wasp’s hijacking of the oak tree, siphoning food out of the nutrient-dense gall. Ultimately, the wasp died.