Giant land crab migrations are one of the natural wonders of Florida. I was lucky to see one, once, years ago. It was evening in early fall. I was driving on A1A along the ocean, north of Vero Beach when the cars ahead started swerving. I approached cautiously and came up on a land crab staring at my car with its stalked eyeballs and pinchers held high. Crabs were everywhere. Some people were trying to avoid hitting the crabs, others were aiming for them, and a third group left their cars and were darting between traffic, trying to catch crabs for dinner. The road was littered with carnage of crabs that didn’t make it across. I recently came upon the land crab above, knew that migration season was coming, and had to learn more about them.
Giant or blue land crabs, (Cardisoma guanhumi) spend their adult life on low-lying land within a couple miles of water. They dig burrows down to the water table that end in a puddle where they can keep moist. Their diet consists of leaves, berries, bugs and occasionally each other. The crabs can withstand a wide range of salinity from fresh to super salty. Low water temperatures restrict their northern range to east central Florida. People like to eat land crabs, particularly in the Caribbean. Gardeners do not like it when crabs dig holes in their yards. Land crabs are gentle creatures and only harm people when fingers get in the way of their powerful pinchers.
At four years land crabs reach sexual maturity. They leave their burrows on full moon nights in late summer looking for love. For two weeks afterwards, females carry between 300,000 and 700,000 developing eggs everywhere they go. Then the migration begins as females travel to the ocean, or sometimes an estuary, to release their eggs. The Florida Fish and Wildlife Commission reduced migration chaos in 2003 by prohibiting catching of land crabs between July 1 and October 31 during the height of their migration. Land crabs must still navigate across roads and around condos but are no longer chased by people who want to drop them into pots of boiling water.
The lucky females make it to the water. Their eggs develop into spiny planktonic larvae. Despite the armor, most larvae end up in the food chain. There’s a reason they lay hundreds of thousands of eggs. The uneaten larvae drift along and go through multiple stages over the next month until they resemble little crabs. These crawl out of the water, scramble up the beach and cross the road. If they escape being eaten or flattened, they dig a burrow on low-lying land and call it home.
Giant land crabs face killer obstacles to survival. Let’s not add plastic to the list. Next time you go to the beach, grab a bag from the BlueTube, pick up plastic and throw it away. Let’s prevent plastic from washing out to sea, breaking into millions of tiny pieces and becoming an inedible meal for larvae. And if you see crabs try to cross the road, let them. We can save the giant land crabs and their wild migrations too!