Mexico’s Annual Land Crab Migration
Tara A. Spears
Each year in coastal Mexico the rains trigger the instinct to reproduce for the tropical land crabs. Since the rains didn’t start until a couple of days ago, the rush is on to get to the ocean to lay eggs. While the females are less brightly colored, you can’t miss this unusual looking creature with suspended eyes, multiple sets of hairy legs and two pincers. 
Identified scientifically as Cardisoma Crassum, this species of land crab can be found in coastal tropical eastern Pacific from Baja California to Peru. Its unique coloration of purplish-blue shell with red legs and lighter colored pinchers makes it easy to spot. It will create burrows as much a five kilometers inland and live all of its life ashore except for mating season.
What makes it possible for C. Crassum crabs to live out of water is the adaptation of gills. In addition, the part of the carapace covering the gills is inflated and equipped with blood vessels. These organs extract oxygen from the air, analogous to the vertebrate lungs. Adult land crabs are terrestrial, but visit the sea periodically, where they breed and their larvae develop. Land crabs are tropical omnivores which sometimes cause considerable damage to crops. The reason for one craw larger is sexual maturity; when of breeding age, the crab advertises with a big claw! This species of land crab can be sizable, growing up to 4.5 inches/ 11 centimeters in width and over 500 grams. Yes, they can be eaten just like the marine crabs.
What’s ecologically beneficial about C. Crassum crab is that a jungle garbage disposal. It is cannibalistic, feeding on leaves, fruits, insects and carrions. Young individuals are often very colorful (leading to a level of popularity in the pet trade), but as land crabs grow older the colors tend to fade. Females may be duller than males. The following photos are land crab left, ocean crab right. Notice the different shell shape between the two types of crab.
However, don’t confuse the tropical blue land crab with the ocean dwelling Blue crabs. The marine crabs are named for their bright tinted sapphire claws; Its shell is actually brown mottled in color. The scientific name of the blue crab, Callinectes sapidus, means “beautiful salty swimmer.” Highly prized for its tender and sweet meat, these crustaceans are among the most heavily harvested in the world.
The ocean dwelling Blue crab is primarily in the Atlantic Ocean or found in brackish coastal lagoons and estuaries from Nova Scotia to the Gulf of Mexico, and from Mexico south to Uruguay. Blue marine crabs are extremely sensitive to changes in their habitat and environment. Constant overexploitation has caused widespread negative effects on the ecosystems they inhabit. Blue crabs are opportunistic feeders, and are important in managing the populations of their prey. They are going to consume mussels, snails, fish, plants, carrion and even smaller, soft-shell blue crabs.
The land crab, C. Crassum is general shy and active at night, but during the migration time you will can see them journeying any time of day on their way to and from the ocean. I’ve even had them on my patio resting in the dog’s water dish! The terristrial crabs are not endangered or threathened, so if you’re ambitious you can chase down dinner.
