Crabs are some of the most successful crustaceans on Earth, thriving in oceans, rivers, and even on dry land. With thousands of species ranging from tiny pea crabs to giants with leg spans over ten feet, they've adapted to nearly every environment imaginable.
Here are the real, verified facts behind these armored, sideways-scuttling survivors.
There are more than 6,700 known species of crabs and crab-like crustaceans worldwide, including roughly 4,500 species of "true crabs."
Crabs are crustaceans, meaning they have a hard exoskeleton, jointed legs, and gills for breathing.
The Japanese spider crab is the largest crab species by leg span, which can stretch up to about 12 feet from claw to claw.
Most crabs have two claws, often one larger than the other, which they use for defense, feeding, and attracting mates.
Crabs can regenerate a lost claw or leg over several molts.
In many crab species, females tend to have a wider, rounder abdomen than males, which helps them carry eggs.
Crabs rely heavily on chemical sensors on their antennae and legs to detect food, mates, and predators.
Most crabs typically walk sideways because of the way their leg joints are hinged, though some species, like the Raninidae, can move forward as well.
Some land crabs, such as certain species of Sesarma, can climb trees and vegetation, and many still need to return to water to release their eggs.
Crabs periodically shed their exoskeleton to grow larger, a process called molting.
Right after molting, a crab's new shell is soft, leaving it vulnerable to predators until it hardens.
Some crab species can shift color over time to better match their surroundings, offering some camouflage from predators.
The horseshoe crab isn't a true crab at all — it's a chelicerate more closely related to spiders and scorpions.
The coconut crab is the largest land-living arthropod on Earth, weighing up to about 9 pounds (4.1 kg).
Some crabs, like fiddler crabs and ghost crabs, make sounds by rubbing or rasping their claws together, a behavior called stridulation.
Most crabs are omnivorous scavengers, eating algae, plant matter, small animals, and organic debris.
The blue crab is a popular seafood species in the United States and is especially associated with Chesapeake Bay and Maryland cuisine.
A few deep-sea crab species are bioluminescent or associate with bioluminescent bacteria, though this trait is rare among crabs overall.
The male fiddler crab has one greatly enlarged claw that it waves to attract mates and fend off rivals, giving the species its name.
Crabs communicate through claw-waving displays, body postures, and chemical signals rather than vocalizations.
Hermit crabs do have a hard exoskeleton on the front of their body, but their soft, curled abdomen is unprotected, so they borrow empty snail shells for cover.
The Japanese spider crab is thought to be one of the longest-lived crabs, with some individuals estimated to live up to 100 years.
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