Leslie Massey
The Christmas Island red crab is a species of land crab native to Christmas Island and the nearby Cocos (Keeling) Islands in the Indian Ocean. These crabs are large, with a carapace measuring up to 116 millimetres (4.6 inches) wide, and are typically bright red, though some can be orange or purple. While they are primarily herbivores, they are not strict vegetarians and will also scavenge and eat other dead animals, including crabs and birds. So, are they safe for human consumption?
| Characteristics | Values |
|---|---|
| Species name | Christmas Island red crab (Gecarcoidea natalis) |
| Diet | Opportunistic omnivorous scavengers; mostly fallen leaves, fruits, flowers, seedlings, dead animals (including cannibalising other red crabs), human rubbish, and the non-native giant African land snail |
| Habitat | Christmas Island and Cocos (Keeling) Islands in the Indian Ocean |
| Population | Estimated 43.7 million adult red crabs on Christmas Island alone |
| Migration | Annual mass migration to the sea to lay their eggs |
| Colour | Bright red, orange, or rarely purple |
| Size | Carapace measuring up to 116 millimetres (4.6 inches) wide; male crabs generally larger than females |
| Behaviour | Solitary outside of the breeding season; sensitive to moisture levels and avoid direct sunlight |
| Toxicity | Not mentioned specifically for this species; some Australian crab species are toxic and should be avoided |
| Edibility | No evidence of Australian red crabs being commonly eaten; other types of crab are consumed in Australia |
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What You'll Learn
Christmas Island red crabs are not poisonous to eat
While some Australian crab species may be toxic if eaten, Christmas Island red crabs are not poisonous to eat. In fact, they are a species of land crab that is endemic to Christmas Island and the Cocos (Keeling) Islands in the Indian Ocean. They are large crabs, with a carapace measuring up to 116 millimetres (4.6 inches) wide and weighing just over a pound. The most common colour is bright red, but some can be orange or, rarely, purple.
Christmas Island red crabs are opportunistic omnivorous scavengers. They mostly eat fallen leaves, fruits, flowers, and seedlings, but they will also feed on dead animals, including cannibalising other red crabs, and human rubbish. They have no natural predators on Christmas Island, although their population has been impacted by the accidental introduction of the yellow crazy ant, which is believed to have killed 10-15 million red crabs in recent years.
During the breeding season, red crabs migrate to the coast to mate and spawn. This annual mass migration is described as an "epic" event, with millions of crabs emerging at the same time, halting road traffic and covering the ground in a thick carpet of crabs. The timing of their migration is linked to the phases of the moon and the beginning of the wet season, usually in October or November.
After mating, the males return to the forest while the females remain in their burrows for another two weeks to lay and incubate their eggs. The eggs hatch upon contact with seawater, and the resulting crab larvae are eaten by fish and large filter feeders such as manta rays and whale sharks. The young crabs then make a 9-day journey to the centre of the island, remaining hidden in rock outcrops and fallen tree branches for the first three years of their lives. It takes about 4-5 years for them to reach sexual maturity and begin participating in the annual migration.
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Crabs are a common food in Australia
There are strict fishing limits in Australia, which can make crab an expensive dish. Most crab species are limited by state fisheries to 20 per person. This makes them costly to market, and often they don't even make it to market. Many Australians catch crabs themselves or know someone who can.
In terms of crab species, mud crabs and sand crabs are the two most common types in Australia. Mud crabs are particularly popular in the Northern Territory. However, it is important to note that not all crabs are safe to eat. Some crab species can carry lethal doses of toxins and should be avoided. These toxic crabs often belong to the family Xanthidae, which is the most diverse family of crabs in Australia and is recognisable by their black-tipped claws.
Overall, while crab is a common food in Australia, it may be less prevalent than other types of seafood, and certain crab species should be avoided due to potential toxicity.
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Christmas Island red crabs are omnivores
It is not advisable to eat Australian red crabs as some species may be toxic. Crustaceans, including crabs, are a significant part of people's diets worldwide, but only a few Australian crab species are harvested for food. Some toxic Australian crab species include the Toxic Reef Crab (Devil Crab), the Mosaic Crab, and the Shawl Crab. These crabs can carry lethal doses of saxitoxin and tetrodotoxin, which can be fatal if consumed.
Christmas Island red crabs, in particular, are not considered edible due to their small size and poor meat quality. They are opportunistic omnivorous scavengers, feeding on a variety of plant and animal matter. They are endemic to Christmas Island and the Cocos (Keeling) Islands in the Indian Ocean. These crabs play a vital role in the ecosystem of these islands, helping to decompose leaf litter, disperse seeds, and provide food for other animals.
Christmas Island red crabs are large, with a carapace measuring up to 116 millimetres (4.6 inches) wide. The male crabs are generally larger than the females, who have a broader abdomen and smaller claws. The most common colour is bright red, but some can be orange or, rarely, purple. These crabs are diurnal, avoiding direct sunlight to prevent drying out and remaining mostly inactive at night.
During most of the year, these crabs live in the forests of Christmas Island and the Cocos (Keeling) Islands. They migrate to the coast to breed during the wet season, usually between October and December. This migration is influenced by the lunar cycle, with crabs spawning before dawn on a receding high tide during the last quarter of the moon. The annual mass migration of millions of red crabs is described as an "epic" event, with the crabs covering the ground in a thick carpet of red.
The breeding migration of Christmas Island red crabs is a spectacular natural phenomenon. These crabs face threats from invasive species such as the yellow crazy ant, which has killed millions of crabs. Conservation efforts are in place to protect the crabs during their migration, as they are vulnerable to being crushed by vehicles.
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Some Australian crab species are toxic
While crabs are a major component of diets worldwide, with eleven million tonnes caught or cultured annually, it is important to note that not all crabs are safe to eat. Some Australian crab species are toxic and can carry lethal doses of toxins. These toxic crabs accumulate toxins in their muscles and egg sacs, which can be harmful to humans if consumed.
Most toxic crabs belong to the family Xanthidae, which is the most diverse family of crabs in Australia and can be identified by their black-tipped claws. While only a small number of species within this family are known to be toxic, it is advisable to avoid consuming them. These crabs do not produce the toxins themselves but may obtain them through their diet or symbiotic bacteria. Saxitoxin and tetrodotoxin, two of the most lethal natural substances known, can be accumulated by these xanthid crabs. As little as half a milligram of these toxins can kill an average-sized human, and cooking the crab meat does not make the toxins any less potent.
The Toxic Reef Crab, also known as the Devil Crab (Zosimus aeneus), is one such toxic species found in Australia. With distinctive colour patterns, this species is relatively easy to identify. The Devil Crab can be highly toxic, and consumption has been linked to fatalities in the Philippines and Timor-Leste. Another toxic species is the Mosaic Crab (Lophozozymus pictor), which, in addition to its bright colours, sports a striking mosaic pattern. This species is found throughout Southeast Asia and Oceania, including the north coast of Australia.
It is important to exercise caution when preparing and consuming seafood. If you are unsure about the species of crab, it is best to avoid eating it. Additionally, it is always a good idea to check with an expert before consuming anything from the ocean.
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Christmas Island red crabs migrate to the sea to lay eggs
Christmas Island red crabs are a species of land crab that is endemic to Christmas Island and the Cocos (Keeling) Islands in the Indian Ocean. They are large crabs, with a carapace measuring up to 116 millimetres (4.6 inches) wide. The male crabs are generally larger than the females, while the adult females have a much broader abdomen and usually have smaller claws. Bright red is their most common colour, but some can be orange or the much rarer purple.
During most of the year, red crabs can be found within Christmas Island's forests. Each year, they migrate to the coast to breed. The beginning of the wet season (usually October or November) increases their activity and stimulates their annual migration. The timing of their migration is also linked to the phases of the moon. During this migration, red crabs abandon their burrows and travel to the coast to mate and spawn. This normally takes at least a week, with the male crabs usually arriving before the females.
Once on the shore, the male crabs excavate burrows, which they must defend from other males. Mating occurs in or near the burrows. After mating, the males return to the forest while the females remain in the burrow for another two weeks. During this period, they lay their eggs and incubate them in their abdominal brood pouch to facilitate their development. Each female crab can produce up to 100,000 eggs, which she holds in a brood pouch. When the moon reaches its last quarter, the egg-laden crabs leave their burrows and gather on the shoreline, packing into shady spots above the waterline. As the high tide starts to turn before dawn, the crabs move into the sea and release their eggs before returning to the forest.
The eggs released by the females immediately hatch upon contact with seawater. Clouds of crab larvae will swirl near the shore until they are swept out to sea, where they remain for 3–4 weeks. During this time, the larvae go through several larval stages, eventually developing into shrimp-like animals called megalopae. The megalopae gather near the shore for 1–2 days before changing into young crabs about 5 mm (0.20 inches) across. The young crabs then leave the water to make a 9-day journey to the centre of the island. For the first three years of their lives, the young crabs will remain hidden in rock outcrops, fallen tree branches, and debris on the forest floor. Red crabs grow slowly, reaching sexual maturity at around 4–5 years, at which point they begin participating in the annual migration.
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Frequently asked questions
Australian red crabs, scientifically known as Gecarcoidea natalis, are a species of land crab native to Christmas Island and the Cocos (Keeling) Islands in the Indian Ocean. They are large crabs with a carapace measuring up to 116 millimetres (4.6 inches) wide. The male crabs are generally larger than the females.
While Australian red crabs are not commonly mentioned as a food source, it is likely safe to consume them as they are not listed as toxic. However, it is important to exercise caution when preparing and consuming any seafood, and if you are unsure about the species, it is best to avoid eating it.
Australian red crabs are opportunistic omnivorous scavengers. They primarily consume fallen leaves, fruits, flowers, and seedlings. However, they will also scavenge and eat dead animals, including other crabs, birds, and the introduced giant African snail.
Australian red crabs have no known natural predators on Christmas Island. However, during their larval stage, millions of red crab larvae are eaten by fish and large filter feeders such as manta rays and whale sharks that visit the island during the breeding season.
Yes, Australian red crabs participate in an annual mass migration to the coast to breed and lay their eggs in the ocean. This migration is described as an "epic" and "spectacular" event, with millions of crabs marching in unison, temporarily halting road traffic and covering the ground in a thick carpet of red.
