An animal is the sum of its parts, including the worms in its genitals

Nematodes, which belong to a different animal group than earthworms, come in tens of thousands of species. Whenever they’re found with insects—which is often—that association is almost always viewed in a negative light. Sometimes the nematodes parasitize or infect the insects; at best, they’re attracted to an insect’s corpse. But after talking to her colleague Erik Ragsdale, who studies nematodes, Ledón-Rettig learned that the worms sometimes harmlessly hitchhike on insect bodies.

First, she examined wild-caught taurus scarabs and saw that they carry one particular nematode species in, of all places, their genitals. “They don’t go anywhere else—not the wings, horns, face, wherever,” Ledón-Rettig says. That makes sense, because the microscopic worms love moisture, and when travelling on a beetle, they need to find sheltered crevices so they don’t dry out. Those particular crevices make it very easy for the nematodes to spread. Adults can transmit them to their sexual partners. Mothers can also pass them to the next generation, by inadvertently inoculating their brood balls with the worms.

That’s a good thing, as Ledón-Rettig discovered. She created brood balls that had either been dosed with nematodes or frozen beforehand to kill off the worms, and showed that beetle larvae grow faster when the worms are around, and eventually transform into bigger adults.

Silvia Bulgheresi of the University of Vienna says this cements the idea that we should think of animals as “holobionts”—a word that refers to the animal itself, as well as the entire community of creatures that shares its life. A dung beetle, for example, is not just an individual, but also the sum of the nematodes in its genitals, the bacteria in its gut, and more. These animals are passing down other animals to the next generation. Anne Estes of the University of Maryland says that the closest analogy, surprisingly enough, might be to humans and dogs.

Or maybe it's like extended cognition, an extended genome ? I'm not really sure this says much about individuality, since the beetles are able to survive without the worms. Obviously they are mutually influential, but a cow and grass have much greater mutual influence but we don't say the cow's individuality is challenged by the grass.

https://www.theatlantic.com/science/archive/2018/10/dung-beetles-sexually-transmitted-worms/571804/