Summer Migration: Tropical Land Crabs
Tara A. Spears
With the summer rain comes the hoard of blue land crabs along the
Land crabs migrate from the jungle to the ocean to wash their eggs during the Mexican summer rainy season, then migrate back to their land territory. That’s why you see so many of the crabs in the summer. These alien-like terrestrial crustaceans have ecological importance as de-composers of dead organisms besides being a human food source.
Land Crab Life Cycle in photos: Adult female blue crab heading to sea; giving birth in the ocean.
Blue land crabs reach sexual maturity in approximately four years. Their peak reproductive activity occurs during full moons in the summer. After mating, an adult female lays her eggs but carries the egg mass beneath her body for approximately 2 weeks prior to
The spawning season (female migration to ocean) lasts from June to December, peaking in October and November. Once the eggs hatch, the tiny larvae are carried out to sea. The development stage (from larvae to small crab) takes about a month out in the ocean; during that time the currents can carry a concentration of larvae quite far before depositing young crabs on another shore. This phenomenon sometimes seems as if an invasion of young land crabs has occurred in an area.
Crabs are usually aggressive towards each other, and males often fight over females. Social and mating behaviors are complex. Many make species – specific sounds by banging on the ground with their pincers or stamping with their feet, or make elaborate pincer movements. Mating occurs only when the female has just molted
This animal can measure up to 6 inches (15cm) across its carapace. In its juvenile form, the crab is a dark brown, purple, or orange in color. As an adult, it is a bluish-gray color. The adult female sometimes appears light gray or white. The reproducing, mature land crab has one claw that is larger than the other, and the walking legs are sparsely hairy.
As adults, the blue crab lives in burrows several feet deep or at least to a level that will allow water to seep in for moisture. The blue land crab is primarily vegetarian, preferring tender leaves, fruits, berries, flowers and some vegetables. Occasionally they will eat beetles or other large insects.
Land crabs have sensitive eyes. During the day they use light and at night they identify the brightest part of the horizon. They also use vibrations, landmarks and prevailing winds to guide them to the sea. It does not depend on its eyes alone, for it senses motion and sound. They can rapidly move in any direction. Their hard pinchers, used for tearing food and protection, will regenerate if torn from its body.
It’s an exotic sign that the tropical summer has arrived when the land crabs move en masse. Like the sea turtles, summer is the time for love and regenerating the species.