On a beach vacation, a poisonous sea slug probably isn’t high on your must-have list.
That’s exactly what San Antonio resident Erick Yanta discovered on his trip to Mustang Island, an 18-mile-wide stretch of land in the Gulf of Mexico near Corpus Christi, Texas.
While walking along the beach, Yanta and his wife, Anna, spotted a tiny blue and white creature no longer than an inch clinging to a rock. He picked it up for a closer look and filmed it before carefully putting it back in the water.
Yanta didn’t know it at the time, but they had encountered the poisonous Glaucus atlanticus, also known as the “blue dragon”.
“We saw a lot of jellyfish like the Portuguese man-of-war, but never this animal,” Yanta said. The Portuguese man-of-war is a siphonophore, a species closely related to jellyfish, according to the National Ocean Service.
As soon as he captured the video, Yanta hopped on Reddit for users to help him identify the animal.
The blue dragon normally lives on the surface of the open ocean, said David Hicks, professor and director of the School of Earth, Environmental and Marine Sciences at the University of Texas Rio Grande Valley in Edinburgh.
The slugs have bright blue underbelly and a softer silver tone on the back, he said. Blue dragons float on their backs so the blue on their undersides can blend into the water while the gray blends into the sea surface, Hicks said.
It’s called countershading, an evolutionary trait that helps animals avoid predators, he said.
Sea slugs can be found on nearly all beaches in tropical and subtropical latitudes, but their small size means most bathers don’t see them, he said.
“They also have a soft body, so they often get broken as they cross the surf zone and are deposited on shore,” Hicks said.
Despite their small size, blue dragons are very powerful with their stinger.
The animal eats creatures like the venomous Portuguese man-of-war and stores its prey’s stinging cells, called cnidocytes, in sacs, Hicks said. Blue dragons will use cells to protect themselves from predators, and humans sometimes get caught in the crossfire.
The pain of being stung resembles a man-of-war bite, which can be quite painful and, in rare cases, life-threatening, Hicks said. Symptoms following a sting can include nausea and vomiting, according to American Oceans.
If you’re stung by a blue dragon, it’s best to go to the hospital for treatment, according to Ocean Info.
Yanta didn’t know the blue dragon he found was poisonous and then laughed when he realized what he had been holding. He said knowing ahead wouldn’t have made a difference.
“I would have done the same,” Yanta said. “I still would have picked it up, filmed it and put it back in the water.”