Ghost Crab

Ghost crabs are one of the most populous crab species in the world and are found on beaches from Oman to Polynesia to Australia to Florida to Egypt and Greece.

Ghost crabs, also called sand crabs, can be told from their boxy shape, their sometimes horned eyestalks, and the uneven size of their claws. They can move surprisingly quickly, and the fewer legs they use the faster they are. Although they use eight of their 10 legs to walk normally, at their fastest only the first and second pairs of their walking legs are in play.

Four Incredible Facts!

• Ghost crabs are only semiterrestrial. Though they lay eggs in water and need to keep their gills wet, they will drown if they stay in the water too long.
• Ghost crabs can make sounds that include bubbling, stridulation, and thumping.
• They can change color to blend in with the sand, one of the adaptations that helps them avoid predators.
• Although they’re small crabs, their larva are among the largest of the crab larvae during the final larval, or megalopa stage.

Classification and Scientific Name

Ghost crabs are members of the subfamily Ocypodinae, which is found in the Ocypodidae family. Ocypode comes from Greek and means “swift-footed,” which describes the surprisingly fast way these crabs can scuttle over the sand. There are two genera in this subfamily: Ocypode and Hoplocypode. In the genus Ocypode, there are 20 species, but there’s only one species in Hoplocypode: H. occidentalis.

Species

Besides Hoplocypode occidentalis, the species of this type of crab are:

• Ocypode africana
• Ocypode brevicornis
• Ocypode ceratophthalma
• Ocypode convexa
• Ocypode cordimanus
• Ocypode cursor
• Ocypode fabricii
• Ocypode gaudichaudii (the painted ghost crab)
• Ocypode jousseaumei
• Ocypode kuhlii
• Ocypode macrocera
• Ocypode madagascariensis
• Ocypode mortoni
• Ocypode pallidula
• Ocypode pauliani
• Ocypode quadrata
• Ocypode rotundata
• Ocypode ryderi
• Ocypode saratan
• Ocypode stimpsoni

Appearance

These crabs have a boxy little body, and most species are pale with the exception of species such as O. gaudichaudii, the painted ghost crab. Their name comes not just from their general pallor, but from the fact that they hunt at night.

Two characteristics that identify ghost crabs are that both the males and the females have claws of different sizes. This differentiates them from their cousins the fiddler crabs, where unequal size claws are found only on the males. The claws of most ghost crabs also have ridges that allow the animal to produce sounds.

Ghost crabs, or sand crabs, also have large and long eyestalks. In some of the Ocypode species, the eyestalks are horned or have stiles. The horns help biologists identify the species. They have huge corneas that are found on an eyestalk’s bottom half.

Their walking legs are longer than the claws. This allows them to move quickly and easily over the sandy beaches where they live.

Distribution, Population, and Habitat

Ghost crabs are found near warmer waters all over the world, like those off the coast of Florida or India. These semiterrestrial crabs dig burrows in sand and mud found in that zone between the high and low tide on beaches on the oceans or estuaries.

There are 21 species of sand crab, and though their habitat has been disrupted by human activity, their population is fairly healthy. Most sand crabs are found in the Indo-Pacific region, while a handful of species are found in the Mediterranean, the Pacific coast of North America, and along the Atlantic Ocean from Massachusetts down to Florida and further south to Brazil.

Predators and Prey

Despite their small size, ghost crabs don’t have a great many predators. Besides the ability to change color, other adaptations that evolved for both hunting and avoiding predation are their speed and their nocturnal lifestyle. Still, ghost crabs are taken by shorebirds and raccoons. The crabs themselves prey on leatherback turtle eggs and hatchlings, which is problematic since the leatherback turtle is endangered. They also eat smaller crabs, other marine arthropods, and insects. Besides hunting for food, ghost crabs are scavengers and cache food in their burrows.

Reproduction and Lifespan

Ghost crabs can mate all year, though there are some species where the female ovulates only in early spring and again in summer. They are unlike other crabs of their Infraorder in that the female can mate when her shell has hardened after a molt. This is one of the adaptations the crabs made when ithey became semiterrestrial.

Males posture and make sounds to both attract females and challenge other males. Usually, the male crabs don’t make contact, but if one doesn’t submit, the stronger one shoves him out of the way.

Fertilization is internal and mating usually happens near the male’s burrow. The sperm comes in a fluid that hardens and forms a plug in the female to make sure her eggs are not fertilized by a rival crab. The female can store sperm for a while, but when the eggs are fertilized, they emerge and stick to her abdomen. Since the eggs look like berries, a female carrying her eggs this way is referred to as berried. The female makes sure the eggs are kept hydrated and may sometimes swim upside down for this purpose.

When the crab larvae hatch, the female shakes them off into the water. They are so tiny at this stage that they become part of the zooplankton and are swept along on the ocean currents.

The baby ghost crab has five molts before it reaches the megalopa stage. It stays in that stage for a little over a month. If it survives to molt one more time, it leaves the sea for the land. Ghost crabs are ready to mate when they are about a year old and have a lifespan of about three years.

Population

The ghost crab population is healthy as of 2021, though it has decreased due to human activity, climate change, and pollution.

Fishing and Cooking

Though ghost crabs are edible, they are considered too small in size to be good eating.

1. Animal Diversity Web, Available here: https://animaldiversity.org/accounts/Ocypode_quadrata/
2. Yesterday's Island, Available here: https://yesterdaysisland.com/ghost-crabs/
3. iNaturalist, Available here: https://www.inaturalist.org/guide_taxa/255131
4. 30A, Available here: https://30a.com/ghost-crabs/
5. Wikipedia, Available here: https://en.wikipedia.org/wiki/Ghost_crab
6. Chesapeake Bay Program, Available here: https://www.chesapeakebay.net/S=0/fieldguide/critter/atlantic_ghost_crab
7. Mexico — Fish, Birds, Crabs, Marine Life, Shells and Terrestrial Life, Available here: https://mexican-fish.com/atlantic-ghost-crab/