40+ Interesting Facts About Crabs

1. Crabs are short-tailed crustaceans, present in marine, freshwater and land environments. There are thousands of known species of crabs on earth. Their closest relatives are shrimp, crayfish, and lobsters. 
2. Animals like king crabs, hermit crabs, coconut crabs, and porcelain crabs are not true crabs, despite their cab-related names. They are related to a different group, commonly known as "false crabs." True crabs are separate from false crabs due to the difference in their leg count, antennae, carapace, and tail. (Source)
3. The coconut crab, also called robber crab, is the heaviest and largest land-living crustacean on earth. It has a maximum leg span of 1 m (39 inches) and can weigh up to 4.1 kg (9 lb). Its primary food is coconuts, while this omnivore animal also eats other animals and plants to survive on remote tropical islands. (Source)
4. Injured or endangered crabs can rip off their claws. However, both adult and younger crabs can regenerate these body parts. Adults can regenerate claws within a year, while this process is faster in juveniles. (Source)
5. Crabs are present in all oceans, along with freshwater and land. Their highest concentration is in tropical and semi-tropical regions of the earth.
6. King crabs have made their place in waters around Antarctica thanks to climate change. This is dangerous because their predatory habits can decrease the population of native Antarctic fauna. (Source)
7. There are several species of freshwater crabs. Most of the crabs in the home aquarium are small freshwater crabs. The few famous ones are red claw crabs, Thai micro crabs, and pom pom crabs.
8. Crab fossils are at least 200 million years old. In 2021, researchers discovered a 100-million-year-old fossil of a crab fully preserved in amber. It is the oldest modern-looking crab and the most complete crab fossil ever discovered. (Source)

   

   Land crabs live most of their life away from oceans
   
   

9. Land crabs are square-bodied that occasionally return to the sea. They live in swamps, mangrove forests, and fields far away from oceans. (Source)
10. The lifespan of crabs is different according to species. A blue crab can live up to 8 years, while a hermit crab can reach 70 years. (Source)
11. Coconut crabs, also known as a robber or palm thief crabs, are very powerful and dangerous. They can carry six times their body weight, while their claws are comparable to a lion’s jaw. The primary food of these crabs is coconuts, but they can also kill and eat birds, pigs, and other coconut crabs. They can even crush the bones of humans with their powerful claws.
12. The Horseshoe crab’s blood color is blue due to the presence of copper-based hemocyanin to transport oxygen. This blood contains extraordinary antibacterial properties, which makes it an ideal substance for testing medical equipment. (Source)
13. A parasitic barnacle, a type of arthropod, infects several crab species. This parasite can deprive the male crab of reproduction and forces it to take care of the host’s eggs. (Source)
14. Crabs usually communicate by rubbing their pincers or claws. However, Atlantic Ghost crabs can also communicate through sounds produced by the gastric mill. It is a teeth-like structure in the stomachs of several crustaceans, including crabs. When disturbed, ghost crabs produce sound by grinding their gastric mill. (Source)
15. Multiple crabs cannot escape from a bucket because if any crab tries to leave the bucket, others pull it back. It is known as the bucket of crabs theory and is synonymous with selfish and jealous persons.
16. Hoff crabs have hairs on their entire belly that harbor numerous bacteria. The crab uses these bacteria as a food source. These crabs live 2000 m. deep in Antarctic waters around hydrothermal vents. Spines on its legs enable the crab to climb chimney-like structures on these vents. Hoff crabs use this ability to live in a place with the right temperature to survive. (Source)
17. Fiddler crabs cannot move their eyes but have almost all-around vision due to their 9000 separate eye facets. They can also see in near UV and other colors.
18. Crabs have a strong and rigid exoskeleton that protects their tender internal organs. This exoskeleton is made of calcium carbonate and chitin (a special protein). The outer layer of this exoskeleton is twice as hard as its inner layer. (Source)
19. A crab’s hard exoskeleton cannot expand when it grows. Therefore, it needs molting (shedding an older shell and growing a new one) every year. Crabs also leave their eye sockets and gills while molting. Females molt in spring, while the molting season for male crabs is summer. (Source)
20. A Carry crab has been filmed carrying an upside-down jellyfish on its back for camouflage and defensive purpose. These crabs are known for using any possible item to cover themselves. (Source)
21. A prehistoric hermit crab was discovered on 25^th June 2009, the day of Michael Jackson’s demise. The scientists who identified this crab named it after Michael Jackson as a tribute to the great pop singer. (Source)
22. Crabs have ten limbs in five pairs. The initial pair acts as pinchers, while the last group of legs in some species is for swimming.
23. There are noticeable differences between both genders of crabs. Male and female crabs are easily distinguishable through their unique claws and undersides.
24. Male fiddler crabs have claws of different sizes, one small and the other oversize. Large claws help them to attract female crabs, and they also use them as an effective weapon. (Source)
25. During the 1990s, Alaskan king crab fishing was known as the most dangerous job. Back then, it had the highest fatality rate in the USA due to drowning. (Source)
26. Pom pom crabs attach sea anemones to their tiny claws as a defensive measure. In return, they help sea anemones to reproduce asexually. (Source)

    

    Pom pom crabs and sea anemones have mutual beneficial relation

    
    
27. There is a visible difference in the size of various crab species. The largest among crabs is the Japanese spider crab, with  body size and a leg span of up to 15 inches and 15 feet, respectively. A Japanese spider crab, named "Big Daddy," was the widest crustacean in captivity and had the longest legs among crabs. (Source)
    
28. The smallest crab is the pea crab, measuring around 6.3 mm. Pea crabs are so small that they live as parasites inside several bivalve molluscs, such as mussels, oysters, and clams. (Source)
29. It is a common assumption that crabs and other crustaceans do not feel pain due to the absence of brain areas associated with pain. However, the latest research shows that crabs and other related animals experience pain with electrical shock. (Source)
30. A female red crab, native to Christmas Island, lays up to 100,000 eggs and then holds them in her abdominal sac. There are more than 120 million red crabs present on Christmas Island. (Source)
31. Hermit crabs have soft defenseless bodies because they cannot grow their shells. Therefore, they use discarded shells of other sea creatures. However, they grow continuously and need new shells timely, while getting them is not simple. They can compensate for this through a process known as a vacancy chain. In this system, all crabs in a community gather when they find a discarded shell. If the shell fits the biggest crab, it will leave its own for the next crab. This cycle continues and all the crabs get their appropriate shells according to their size. (Source)
32. Most crabs walk sideways due to the structure and position of their legs. The second joint in the crab’s legs bends only sideways. Therefore, the animal walks efficiently sideways instead of the forward movement. (Source)
33. Unlike most crabs, some species can easily walk forward or backward. A prominent example is the soldier crab that walks forward thanks to its unique body shape. (Source)
34. Most crabs walk across the ocean bottom. Few species, like blue crabs, can swim thanks to the unique shape of their rearmost pair of legs.
35. Sand bubbler crabs are small crabs, living on sand beaches in the Indo-Pacific region. They are famous for making small sand balls on these beaches. These sand balls are pallets of the food they consume. 
36. Crabs, both in the wild and as a pet, are omnivores that eat from plant and animal sources. Their diet differs according to the size and includes seaweed, algae, shrimp, small fish, mussels, snails, and other crabs.
37. People around the globe like to eat crabs. They provide several nutritious ingredients, including easily digestible protein, omega-3 fatty acids, vitamin B2, phosphorus, copper, and selenium.
38. King crabs are the largest edible crabs in the world. A Russian scientist introduced these crabs to Norway in the 1960s without asking permission from the host country. (Source)
39. Different crab species are known for mass migrations in various parts of the world. These crab migrations happen toward the sea during mating season. A few famous crab migrations include Red crabs’ migration in Christmas Island (Australia) and Cuba, Horseshoe crabs’ migration in Delaware Bay, Soldier crabs’ migration in Caribbean Islands, Blue crabs’ migration in the Chesapeake Bay, and Red King crabs’ migration in Alaska. (Source)
40. In Australia, there is a bridge over a busy road on Christmas Island. The reason behind the construction of this bridge is to assist the annual migration of 50 million crabs. (Source)
41. Humans are the main predators of crabs. They are also on the menu of several other land, marine, and flying animals, including raccoons, alligators, otters, turtles, fish, and birds.
42. Derelict crab traps are lost or discarded fishing gear. These "ghost gear" kill numerous crabs and other marine animals in water bodies around the globe. Only in Chesapeake Bay, these traps kill nearly 3.3 million crabs annually. (Source)