Hermit crabs face a uniquely competitive real estate market. They need bigger and bigger shells throughout their lives, but can’t grow these homes themselves. So they rely on castoff snail shells, and are constantly on the lookout for better properties entering the market.

A study that will be published next month in the journal Physica A found that the distribution of these shells in one hermit crab population was surprisingly similar to the distribution of wealth in human societies.

That may make hermit crabs one of the first animals known to experience wealth inequality.

Ivan Chase, an emeritus professor at Stony Brook University in New York and the study’s lead author, researches social systems in animals and described a phenomenon called the vacancy chain in hermit crabs in the 1980s.

When a snail dies on the beach, a crab that comes across the empty shell will inspect it closely, turning the shell over in its claws. If the crab decides this home is better than its current shell, it trades up. Another, usually smaller crab may soon find that crab’s castoff and move in. Each vacancy lets about three crabs upgrade their shells, Dr. Chase said.