This news story about a seashore snail found living in a child’s knee wound has been making the rounds lately.

Apparently 4-year old Paul Franklin from Southern California was camping at a beach in central California near Morro Bay, when he fell and hurt his knee (Orange County Register). For several weeks afterwards, the wound refused to heal fully, despite the use of antibiotics. Eventually mom squeezed the wound, and out popped a little snail. Viewers around the world made disgusted noises in response. The story seems almost too fantastic to believe at first, but I do believe it could be legitimate. Here’s why:

Although the available video is low quality (thanks local news!), the snail they’re showing off looks like a littorine snail, specifically Littorina keenae, or possibly the related species Littorina scutulata. These snails are near and dear to my heart, since I wrote a chunk of my PhD thesis about Littorina keenae and its relatives.

Snails in the genus Littorina and affiliated genera are found living high on the shore in the rocky intertidal and marshes around the world. They make their living scraping microscopic algae off of the rocks and marsh plants, and generally avoid being submerged in the ocean for long periods of time. Littorina keenae and Littorina scutulata in particular are found all over high shore rocks along most of California’s coast,  where this child was playing when he scraped his knee. So L. keenae would have been in the right place for this kid to scrape his knee and pick one up.

Littorina snails are typically very small, even as adults, so it’s easy to fit one under your skin. L. keenae can become reproductive adults by the time the shell length hits approximately 5 mm, which is roughly the size of the snail shown in the video.

Littorine snails are renowned for their toughness, particularly when it comes to surviving for long periods without food or water, and surviving high temperatures (like those inside a kid’s knee). George Somero published a paper in 2002 showing L. keenae will survive temperatures above 44-45 °C (113°F) for 3 hours. David Marshall and co-authors have demonstrated even more robust temperature and desiccation tolerance in tropical littorine species.  During the course of my studies, I managed to leave several L. keenae sitting on the desk in my office for at least 6 months, where they sat without food or water and regularly saw temperatures above 26°C (80°F) during the day, and yet they opened right up and started crawling around when put back into seawater. It’s not inconceivable that this child’s snail (“Turbo”) could have sealed itself up and patiently waited inside its shell, inside his knee, for the three or so weeks it took to find the snail. An important point to note is that most other sea snails cannot survive for this length of time at those high temperatures, especially without food or seawater. Among all of the snail species found on the seashore in California, the littorine snails are uniquely suited for living inside a wound.

The snail shown in the video almost certainly got inserted into the kid’s skin at the size shown in the video, not as a larva or egg or even a smaller version of the snail you saw. L. keenae takes months to grow from a microscopic juvenile to the size shown in the video. Baby L. keenae are released into the ocean as eggs, where they float in the water column for some period of time before they settle back onto the shore as tiny snails. There are no littorine snail eggs or larvae on the rocks to get shoved into a wound. The snails shown in the video would have had nothing to eat inside the kid’s leg (remember, they eat algae, not meat), so it couldn’t have done much growing in that time.