Halloween this year may be strange — and that’s saying something because it’s a weird holiday in normal years — but the Halloween Moon Crab will be not be changed by the oddities of 2020.
This tropical animal gets its name from the rich colors of its body which consists of a black carapace (upper shell), bright red-orange legs and purple claws. These are perfect colors for this holiday, combining witches and pumpkins. On top of that, these crabs also have a few bright spots — some yellow, some white — on their carapace, bringing to mind candy corn.
This crab is found in sand dunes, mangroves and rain forests along the Pacific coast of Central America and Mexico. Halloween Moon Crabs are especially common in Nicaragua, Costa Rica and Panama. Despite the large numbers of these animals present all along the coast, they are only rarely seen during the dry season, which can last six months.
Desiccation is a constant danger to them during this time of the year, and they spend most of their time in burrows in the forest. They dig their own burrows, which can be 1.5 meters deep. They stay in these hideaways, only coming out at night to forage for leaf litter and other plant matter, which they bring to their burrows to eat.
When the first rains come, they storm the beaches like it’s the zombie apocalypse, with thousands of them going toward the ocean simultaneously. The reason they are all heading that way is because their breeding behavior is triggered by the first rain.
Their synchronous breeding at the beginning of the rainy season may be a form of protection against the threat of predation. As is true for a variety of species of birds, insects and sea turtles, it is advantageous for large numbers of Halloween Moon Crabs to breed at the same time because the risk of predation of their young is lessened by the safety in numbers principle. Predators can only eat so much at once, and the mass spawning swamps the environment with more potential prey than predators can consume.
These crabs do continue to breed throughout the rainy season, but the largest breeding event is at the beginning following the first rains. Females lay their eggs soon after, often with the second rain of the season. They release their eggs in outgoing tides, which may be another mechanism to prevent predation of the young. The eggs hatch into a larval form called a zoea, which has several developmental stages, and then change into a larval form called a megalopa, and then finally into a juvenile crab which heads to shore. Once on land, it continues its development until it turns into an adult crab of up to 5 centimeters in size. Though Halloween Moon Crabs breed and begin developing in the water, they spend most of their lives — up to 10 years — on land.
Don’t be a crab this Halloween, unless it’s your costume. Then, you should absolutely be a Halloween Moon Crab.
Karen B. London, Ph.D. is a Certified Applied Animal Behaviorist, Certified Professional Dog Trainer, author, and an Adjunct Faculty in NAU’s Department of Biological Sciences.
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October 20, 2020 at 08:00PM
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