Stealing Stings

Thieves are lurking below the surface of the oceans. These thieves are colorful sea slugs called nudibranchs. They’re found in ocean waters all over the world.

Sea slugs don’t have a shell. They aren’t spiny. So how do they stay safe? They steal the ability to sting from other sea creatures. They’re able to store this ability for later.

STINGING BEAUTY Spanish shawl nudibranchs get their bright colors from the stinging creatures they eat. Their colors indicate to predators that they’re poisonous.

Jessica Goodheart says nudibranchs are like tiny pirates. “Pirates go to other ships and pillage,” she told TIME for Kids. “They take their [enemies’] weapons, and that is kind of what these slugs are doing.” Goodheart is a professor and an assistant curator at the American Museum of Natural History, in New York City. She and her team are studying this animal ability.

Stay Away

There are 3,000 species of nudibranchs. One group is covered in soft spikes called cerata. These body parts are used for breathing. They’re also used for storing and dispensing stings.

SOFT SPIKES The cerata covering this sea slug help the animal breathe. Their tips carry a painful sting.

Nudibranchs eat stinging creatures such as jellyfish. The tentacles of these animals are lined with venom-filled cells × cell one of the tiny units that make up all living things (noun) . These cells eject tiny harpoons called nematocysts. That’s how the animals sting.

Nudibranchs, though, are not affected by nematocysts. They swallow them and store the tiny harpoons in their cerata. When a predator tries to eat them: ouch! They get “a mouthful of these stinging structures, and any venom that comes with them,” Goodheart says.

SMALL BUT MIGHTY The blue dragon nudibranch eats venomous men-of-war.

New Possibilities

Goodheart wants to understand why nudibranchs are not harmed by nematocysts. Living things have cells that take in and break down foreign objects. For example, cells in the immune system take in bad bacteria and break them down. But nudibranchs’ cells don’t break down nematocysts. How do nudibranchs eat a stinging cell “without destroying it?” Goodheart asks. She published a study in June 2025 that found some answers.

Goodheart and her team looked closely at different parts of a nudibranch. They found that the cells that store the stings are not directly involved with immunity. The cells are not involved with digestion, either. So they don’t destroy or digest the nematocysts.

IN THE FIELD Jessica Goodheart scuba dives in search of nudibranchs. She also studies them in her lab.

The cells are very specialized. They might help Goodheart understand how the human immune system can adapt × adapt to change or adjust (verb) . Imagine a nematocyst carrying medicine. A blood cell could pick up that nematocyst without destroying it. The nematocyst could “release [the medicine] in an area that you want to specifically deliver it,” Goodheart says. This would be a medicine-delivery system adapted from slugs. Scientists are investigating the possibilities.

SLUG SNAPSHOT An Australian sea slug poses for Goodheart.

Sea Grazing

The Costasiella sea slug is sometimes referred to as a leaf sheep slug. Its cerata are green, so it resembles a plant.

Unlike other nudibranchs, the Costasiella does not steal stings. Instead, it eats seaweed and steals the structures that give the seaweed its green color. This allows the slug to perform photosynthesis. That’s a process that turns the sun’s rays into energy. Maybe you’ve heard of photosynthesis in plants. The Costasiella uses it too.