Every year in late September and early October, something remarkable happens in Cancún. As the full moon rises over the Caribbean, thousands of giant blue land crabs (Cardisoma guanhumi ) begin an ancient journey from the mangroves of the Nichupté Lagoon to the sea. Their goal: to lay eggs in saltwater, continuing a reproductive cycle that has played out for generations.
The path of the blue crabs of Cancun—once wild and unbroken—is now bisected by busy roads and the ever-expanding infrastructure of a modern resort city. What was once a purely natural migration has become a dangerous crossing.
Before Cancún became a major tourist destination, these crabs faced only natural predators—herons, egrets, racoons, foxes, snakes and even igunanas. Today, they must navigate a maze of pavement, headlights, and fast-moving traffic. It’s not uncommon to see the roads that cut through the Hotel Zone littered with crabs—some moving purposefully toward the beach—others are not so lucky.
A Community Comes Together
In response, local environmentalists, government agencies, and concerned residents launched the Blue Crab Protection Campaign in 1991. Coordinated by the General Directorate of Ecology, the campaign runs in two phases each year, one in September and another in October, timed to the crabs’ peak activity during full moons.
It’s become a beloved tradition in Cancún. Families with children, students, and volunteers of all ages gather during migration nights with gloves, buckets, plastic containers, and flashlights in hand. They carefully scoop up the crabs and carry them across the road, releasing them safely on the beach side.
Public awareness campaigns also play a role, with signs and announcements encouraging motorists to slow down during these nights. Thanks to these collective efforts, thousands of crabs are saved each year.
Why It Happens
The migration is tied to seasonal rains and lunar phases. Heavy rains prompt adult female crabs to leave their burrows and begin the trek to the sea. The wetter the season, the larger the migration. Mating typically occurs between July and September, and by late September, many females are carrying fertilized eggs externally.
Each gravid female carries between 20,000 and 1,200,000 eggs externally for about two weeks before heading to the sea to release them. Once the crabs reach the water, the eggs are released into the sea. After about two weeks, the larvae hatch, and in roughly 42 days, they develop into tiny juvenile crabs ready to return inland. Without reaching saltwater, however, the eggs won’t survive—making the migration not just important, but essential.
Meet the Blue Crab
Blue land crabs are some of the largest terrestrial crabs in the region, capable of growing up to 14 inches across and weighing more than a pound. Their coloration shifts with age: juveniles tend to be orange or brown, while adults turn a distinctive bluish-gray. Blue land crabs typically molt once a year, sealing themselves inside burrows beforehand to safely shed and regrow their exoskeleton. Post-molt, they remain vulnerable until their shell hardens.
They’re omnivorous, but mainly consume plant material like fruits, mangrove leaves, and occasionally carrion or insects. Primarily terrestrial, these crabs reside in burrows—sometimes over 2 m deep—in mangrove swamps, muddy coastal areas, and even inland up to 5 miles from the shore, as long as they can access water. The crabs venture out of their holes primarily at night. During the day, they’re well-hidden—making the nighttime migration all the more visible and striking.
Although not currently endangered, populations are declining in some regions due to habitat loss, pollution, and overharvesting for food or traditional medicinal use. Conservation strategies—including regulated trapping and community-based education—are being successfully implemented in areas like Brazil, Colombia and right here in Cancun.
Want to Help?
If you’re in Cancún during the migration period, you can take part. It’s a hands-on way to contribute to a local conservation effort with real impact. Ask your hotel or check with the General Directorate of Ecology to find out where and when volunteer groups will gather.
Just bring gloves, a bucket, and a flashlight—and wear closed-toe shoes. It’s simple, safe, and surprisingly rewarding. You’ll be helping an important species survive in an increasingly urbanized landscape.
And if you’re driving through the Hotel Zone on a warm, rainy night under a full moon—slow down. You might just find yourself sharing the road with one of Cancún’s most ancient residents, still trying to reach the sea.
