It’s true: Crabs keep turning up in nature, and it’s bothering scientists so much that they’ve been given federal grants to get to the bottom of it.

The phenomenon is so widely known that it’s been given a name—carcinization, a term that’s been in use for over 140 years. Through this process, crabs, the beach critters we all know and love, have evolved at least five times from separate groups of crustaceans, Newsweek has been told.

These groups had one common ancestor, but over 300 million years ago. That means there’s been a lot of time for evolution, but still the crabs keep coming.

“Carcinization can be defined as the evolutionary process leading to the crab-like form,” said Heather Bracken-Grissom, associate professor at the Institute of Environment and Department of Biological Sciences at Florida International University, who has been studying the phenomenon.

“We know the process has occurred multiple times and our current grant is aimed at better understanding the drivers and implications.”

Not all the species to have undergone carcinization have become crabs in the technical sense. Some have merely become crab-like, adopting their shape and form. Carcinized species can be divided into