Solar-Powered Slugs Hide Wild Secrets—But They’re Vanishing

Life has certain rules and patterns. Plants, with their incredible ability to harness the sun’s energy, don’t go roaming around. They don’t need to. But animals, lacking the wondrous power of photosynthesis, do. They trot, slither, flap. They seek out plants and they eat them.

They most certainly do not photosynthesize, the animal playbook would seem to dictate. That’s a plant’s role.

But one small sea slug does not care for such rules, thank you very much.

These animals, Elysia chlorotica, which live off the U.S. East Coast, are not merely content to glide about munching algae. Instead, they steal the molecular engines that allow plants to harvest solar energy. The slugs take up these mini-machines, called chloroplasts, into their skin, which turns them emerald green.

Experiments have shown that this sea slug, which looks like a little leaf an inch or two in length, can go without eating for nine months or more, photosynthesizing with its stolen plant-parts as it basks in the sun.

“It’s unique; it’s controversial; it’s elusive; it never eats,” says Patrick Krug, a biologist at California State University, Los Angeles. “Basically your typical L.A. celebrity.”

Though other sea slugs can purloin chloroplasts and use them to catch some rays, none come close to doing it as well as Elysia chlorotica.