There are more than 4,500 species of crabs that come in a variety of sizes. The most common crabs are about the size of your hand. However, the giant Japanese spider crab has a body that is 15 inches across and legs that can span up to 12 feet from the tip of one pincer to the next. The tiniest crab is the pea crab, and as the name suggests, it is the size of a pea. Most crabs live in the ocean or along the beaches, but some species are found in freshwater and estuaries. Let’s take a look at how these crabs hunt and what crabs eat.
How Do Crabs Hunt?
With so many crab species, there are some variations in how they hunt. For example, the Dungeness crab will scour the ocean floor searching for prey, using its large claws to snatch passing squid. The red king crab has one claw that is larger than the other, which it uses to crush its prey. The fiddler crab also has one claw that is larger than the other, but it uses the larger claw for combat and the smaller claw to sift through the sand in search of food. The blue crab uses camouflage to ambush its prey.
Yet, how do crabs find their prey? Crabs have sensory receptors on their antennae that allow them to detect chemicals in the water emitted by their prey. They also have compound eyes that give them a panoramic view of their surroundings. Additionally, they are sensitive to UV light, which helps them detect movement more easily.
What Do Crabs Eat?

Fiddler crabs use the large claw for combat and to attract mates, while the smaller claw is used to feed.
©iStock.com/sdbower
Most crabs have an omnivorous diet. Smaller crabs eat algae, seaweed, worms, small clams, and shrimp. Larger crabs eat squid, snails, mussels, other crabs, and small fish. Some species of crabs can eat hard foods like barnacles, starfish, and even sand dollars. There are even some crabs that are opportunistic scavengers, feeding on dead animals and decaying plant matter.
Although there are some variations depending on species, here is a list of foods crabs eat:
- Small fish
- Smaller crabs
- Crustaceans
- Shrimp
- Krill
- Prawn
- Squid
- Small clams
- Seaweed
- Mussels
- Whelks
- Algae
- Worms and other invertebrates
- Carrion and decaying plant matter
Of course, crabs that live in different habitats have access to different foods. For example, freshwater crabs tend to eat more algae, vegetation, and insects because they are limited by their environment. However, marine crabs have a more diverse diet because of the greater variety of prey found in the ocean.
What Eats Crabs?

Sea otters enjoy eating crabs, especially Alaskan king crabs.
©Jean-Edouard Rozey/Shutterstock.com
If you’ve ever had crab legs with butter sauce, you know that humans eat crabs. Popular crabs for cooking include blue crab, Dungeness crab, snow crab, and Alaskan king crab, to name a few. In the wild, many different animals prey on crabs, depending on their habitat. Birds such as gulls and herons often eat crabs. Sea turtles, octopuses, sharks, large fish, lobsters, and other crabs also prey on crabs. Sea otters and seals regularly eat crabs as well.
Because crabs have an exoskeleton, they must molt to grow. During molting, crabs shed their old shell and withdraw their antennae, eyestalks, mouthparts, gills, and legs from it, emerging with a new, soft shell. The new shell begins to harden after a few days, but it takes about a month to fully harden. As a result, molting leaves juvenile crabs especially vulnerable to predators until their new shell hardens.
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