The moon crab is a beautiful species of crab known for its bright and bold coloration. More commonly known as the Halloween crab or Halloween moon crab, these crabs exhibit a dark inky black carapace, bright orange to red legs, and purple claws.
Known scientifically as Gecarcinus quadratus, moon crabs are native to the rain forests of Costa Rica. Similar to hermit crabs, moon crabs are terrestrial, or land dwelling, and spend their adult lives living along the sandy shores of beaches but may also live inland up to over a quarter a mile away from water. Although they live on dry ground, moon crabs must return to a water source to keep their gills from drying out. They are able to inhabit both fresh and salt water but only reproduce in the ocean waters.
Moon crabs grow to approximately 2-2.5 inches and are nocturnal. During the day, moon crabs burrow under the sand or find other places to hide until night falls in which they emerge to forage for food. Moon crabs are considered scavengers and will eat both plant and animal matter including leaves, seeds, fruit, and fish. They will also climb trees in search of food.
Determining the sex of moon crabs is primarily based on the coloration of the crabs. Males are typically much brighter in color and have legs that are more on the reddish side while females have colors that are washed out and legs that are a lighter orange. As mentioned previously, moon crabs return to the ocean to reproduce. After mating, females release eggs into the water where they hatch into larvae that drift along in the plankton rich surface waters. The larvae go through several development stages during this time and feed upon the microorganisms that inhabit the water. Young moon crabs that have completed their juvenile stages of life will then emerge from the ocean waters to begin their lives on dry land.
Moon crabs can also be kept successfully as pets. As long as a few basic requirements are met, these crabs can live happily in captivity where they can reach an age of up to ten years. One crab can be kept by itself in a ten gallon aquarium but any additional crabs will need more room as they are territorrial and will compete for food. A temperature of 75-85 degrees Fahrenheit must be maintained at all times as these crabs are tropical. A basic set up includes a sandy substrate for the moon crab to burrow into, 2 containers of water (one salt water and one fresh), rocks and branches for climbing, and an additional hiding place that is above the ground. Moon crabs can be fed hermit crab food obtained from a pet store and fresh fruits and vegetables. Dead fish may also be given along with their bones as this lends additional calcium to keep the crab’s shell healthy.
All moon crabs sold as pets are wild caught but will adapt to captivity. Because they need specific ocean conditions to reproduce, moon crabs have not been successfully bred in captivity.