Mexican Land Crab Migration Delayed
Tara A. Spears
One of my favorite natural events in coastal Mexico is the annual land crab migration. But with the delayed onset of the rainy season- which triggers the instinct to reproduce for the tropical land crabs- I was concerned for the species. Since the rains didn’t start until July this year, the clock is ticking for the crabs to get to the ocean to lay eggs. While the females are less brightly colored, you can’t miss this unusual looking creature with extended eyes, multiple sets of hairy legs and two pincers.
Scientifically identified 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, living 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.
From a conservation perspective the Blue Land Crab has not been formally evaluated. They are an important food source in southern Mexico where they are caught by hand and sold fresh in local markets. Crabs are subject to a high level of illegal commercial exploitation, including their utilization by the pet trade due to their attractive colors. They are also consumed in abundance by alligators, birds and raccoons. However, don’t confuse the tropical blue land crab with the ocean dwelling Blue crabs.
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 terrestrial crabs are not endangered or threatened, so if you’re ambitious you can chase down dinner.
