Tasmanian Giant Crab Profile
Crabs appear in the fossil record as far back as 250 million years. In that time they’ve evolved to move from water to land, and then back again between 7 and 17 times.
Today they make up 7,600 species across 109 families and range in size from a few centimetres to around four metres across. The largest of them all, the Japanese spider crab, is a true armoured giant, but 8,000km South of Japan is a species that comes in a very close second.
The Tasmanian giant crab is the lesser-known of the two: a stockier, yet equally heavy crustacean that is commonly seen off the continental shelf of Southern Australia, yet still very poorly understood.
Tasmanian Giant Crab Facts Overview
| Habitat: | Marine, continental shelf, 20 to 820 metres (66–2,690 ft) deep |
| Location: | Southern Australia |
| Lifespan: | Around 30 years |
| Size: | Carapace of up to 46 cm (18 in), large claw can reach 43 cm (17 in) long |
| Weight: | Up to 17.6 kg (39 lb) |
| Colour: | Red and white |
| Diet: | Carrion, gastropods, crustaceans, starfish, conspecifics |
| Predators: | Probably octopuses, humans, other crabs |
| Top Speed: | Slow |
| No. of Species: | 1 |
| Conservation Status: | Not Listed (IUCN) |
Tasmanian giant crabs truly live up to their name. Unlike many who claim the title, these are true crabs and have been keystone species in their ecosystems for over 35 million years.
They are one of the largest arthropods in the world and represent the crab lineage well by being slow-moving, impenetrable devourers of everything in their path.
While limited by ocean temperatures, they move up and down in the water column, growing from tiny eggs into gargantuan killers.
Yet, despite their size, they’re not well-researched and may be vulnerable to commercial fishing trends.
Interesting Tasmanian Giant Crab Facts
1. They’re crabs
This might seem like a lazy factoid to get us started, perhaps even a sneaky attempt to reach the word count without having to do any research. But don’t be so cynical!
Crabs are crustaceans, specifically, crustaceans in the infraorder Brachyura. But there are multiple branches of unrelated crustaceans that have evolved to be distinctly crab-like.
Hermit crabs, king crabs, and Porcelain crabs are all examples of non-crabs that end up on crabby Top Ten lists nonetheless.
Through a process called Carcinisation, many crustacean lines independently evolved to look a lot like crabs simply because that phenotype is so good at doing what it does. So, when you read that the so-called coconut crab is the third heaviest crab, you need to be a little sceptical, knowing that it’s actually a hermit crab.
Fortunately, when you read that the Tasmanian giant crab is the second-largest, you can rest easy that it’s actually true. This is despite the genus Pseudocarcinus translating roughly to “False crab”. 1
2. They’re monsters
These huge crabs are heavily armoured, with enormous, powerful claws. They embody the driving force of tank-like crustacean life by moving slowly and methodically, devouring more or less anything organic they come across.
Life isn’t fast for a giant crab, and after their larvae have stopped floating about on the currents, they will moult every three to four years, each time jumping up in size. As adults, this routine slows to once every nine or so years.
Since mating only happens after a moult, this means they have to make the most of each one. But females can store sperm for up to four years and will use it to make a batch of eggs each year until it runs out. The number of eggs increases with the size of the female, which can be truly enormous.
During their lives, they’ll feed indiscriminately.
3. They’re cannibals
Arthropod cognition is an emerging avenue of research that is continually building on our new understanding that invertebrates have feelings.
A report from the London School of Economics found that there is plenty of evidence that crabs are sentient, and considering our historical ignorance towards animals in general – and even humans from unfamiliar places – this shouldn’t be all that surprising.
But crabs certainly hide it well. They move, they eat, they move, they eat, they kill, they mate, and they never appear all that interested in nuance. The apparent mindless monotony of crab behaviour can only truly be unveiled in the lab, and when studied, they still behave quite monstrously.
Cannibalism appears to be common among these crabs, and one study showed that it relates to the length of the photoperiod.
Tasmanian crabs kept in long periods of light would turn on one another a lot more than those kept in total darkness, which might suggest one reason why they move up and down from shallow to deep waters throughout their lives. 2
4. They engage in vertical migrations
These crabs can’t control their body temperature like most vertebrates can, so they need to stay within a comfortable thermal gradient.
Fortunately for them, they live on the steep continental shelf, where the continental crust gives way to the denser oceanic crust. This essentially allows them to climb from cold, deep waters, to warmer shallower ones and back again as needed.
Hiding in the depths, as we’ve discussed, keeps them safe from other crabs, but it’s cold. It’s a good place to conserve energy when they’re not feeding but to find lunch, they need to move into warmer waters.
But when moulting, their new shells take time to harden and the crabs are more vulnerable to predation, so females descend to the darkness during this time, too.
Seasonal changes in temperature and food abundance explain their general pattern of movement up and down, and it appears that females also descend to produce eggs, which they can do in copious amounts.
5. Two million eggs
When producing eggs, females will change colour. This occurs around June and July and coincides with a fresh moult or the anniversary of one.
Females carry an average of around 1.5 million eggs, and a particularly large specimen can have up to two million in a clutch.
These eggs will become free-floating larvae for around 50 days, depending on the temperature, and will then sink to the sea floor and begin the slow process of becoming a monster.
6. But they’re docile
Strangely, despite their cold and destructive appearance, these are generally easy animals to handle.
An Australian-owned company, the bafflingly named Eaglehawk Dive Centre has created one of the most American videos on the internet.
Set to a backdrop of motivational ‘80s generic synth, it shows just how slow and calm these giant animals are; divers can be seen approaching, picking up and even cuddling with the crab.
This is likely a product of their slow metabolisms, but it’s nice to think they just like to be hugged.
7. They’re not well-known
The vast majority of information on this species comes from fisheries data. As with any animal that moves up and down in the water column, there is a sampling bias that occurs from how deep the nets or pots were set.
When females descend to mate, only males are caught in the shallows. This gives the false impression that there are more males than females.
Likewise, when reproducing females are in hiding, most of the females caught are not with eggs.
Essentially, the data is concerningly limited and this species isn’t even listed on the IUCN Red List because of it. Concentrated marine biological research should be introduced to fill in the gaps before the species becomes at risk of extinction from overfishing. 3
Tasmanian Giant Crab Fact-File Summary
Scientific Classification
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Malacostraca |
| Order: | Decapoda |
| Family: | Menippidae |
| Genus: | Pseudocarcinus |
| Species: | gigas |
Fact Sources & References
- Marie Look (2024), “The Biggest Crab in the World, Plus 8 Enormous Contenders”, howstuffworks.
- Alison Bosman (2022), “Do crabs and lobsters have emotions and feelings?”, earth.com.
- “Giant Crab Fishery”, Fishing Tasmania.