Crabs are known for an interesting scuttling walk, with long pincers in the front.
Found in many areas of the world, on both land and in water, varying species of crabs are excellent foragers, scavengers, and hunters, eating a variety of foods.
Crabs eat shrimp and many other things. Most species are omnivores, eating foods such as algae, fish, seaweed, worms, oysters, plant matter, and more. Different species and sizes of crabs will access larger or hard-textured food sources in their diets such as squid, barnacles, or starfish. In general, crabs will consume just about anything in order to meet their daily caloric needs.
This article offers additional detailed information about the different ways in which crabs obtain food.
Crabs are crustaceans, along with lobsters and shrimp. Crustaceans are water animals with segmented bodies, an outer shell, antennae, and jointed limbs.
Many crab species walk or crawl sideways on five pairs of legs, and a few will move forwards or backward. They use their jointed and paddle-shaped legs to expertly swim, or walk on sand, uneven terrain, or the water’s bottom.
There are over 4,500 species of crabs found in both fresh and marine waters as well as on land. Land crabs typically access marine waters during their early stages of life as well as for food sources.
Crabs eat an omnivorous diet, acting as scavengers or exhibiting predatory behaviors. They will eat other crustaceans, including shrimp, as well as other proteins and plant materials.
The size and claw morphology can vary in crab species, affecting the way they obtain food.
How Crabs Eat
Crabs consume a lot of food in small amounts, needing sources of calcium for their exoskeletons which shed (molt) and regrow as they increase in size.
For pet crab owners, crabs are often fed once or twice a day to keep them satisfied, thus preventing them from consuming any tankmates.
This video shows a crab eating a live shrimp:
The following ways have been observed in how crabs obtain food:
The size of the crab and the strength of its claws affect the size of the prey and if it can break through the hard outer shell of other creatures.
Crabs have sensitive chemoreceptors, acting like taste buds, on their antennae that help them to detect acceptable prey or food sources.
Most species of crabs have a pair of long pincers or claws (chelipeds) to catch prey. One claw may be bigger than the other for fighting, attracting females (in males), or is the crusher claw.
Generally, one claw, (such as the crusher claw) will crush and hold prey, and the other claw tears off small pieces for consumption.
Some crabs use their pincers alternatively to crush, instead of one being dominant.
Crabs can also obtain organisms that burrow, by using their claws to dig or break up materials where food sources are hiding. The prey is then captured, broken up, and consumed using the crab’s chelipeds.
Crabs will hide in crevices or other places, or camouflage themselves, waiting for prey to come close.
For example, spider crabs (Macrocheira kaempferi) which cover their shells with zoophytes or seaweed to disguise them as they wait for prey.
Blue crabs (Callinectes sapidus) shelter in underwater grasses for protection and to feed on plant matter and small invertebrates.
Standard Foraging And Scavenging
Crabs obtain plant materials and carcass food sources (scavenging) by skimming over the substrate (bottom surface), breaking up sources with their chelipeds, and consuming them.
Foraging Without Using Chelipeds
The crab will stretch out its body along the bottom surface (substrate), and break up or scratch at food sources with oral appendages.
Crabs can do this while moving or standing still.
In addition to scavenging, some crabs use other creatures and the surrounding habitat to assist them in obtaining food.
For example, the pea crab (Pinnotheres pisum) lives as a parasite in mussels’ shells and other bivalves (2-hinged bodied creatures), sharing the hosts’ food sources.
Predatory Feeding on Sessile And Sedentary Creatures
Sessile organisms (immovable, including plants) and sedentary creatures are easy food sources for crabs.
The crab will attach itself to the source or climb onto it, using its claws and oral appendages to effectively consume it without any need for fighting.
The crab’s powerful claws can also be used to scratch or break hard outer shells of food sources.
If the crab is injured or missing a limb, it will use its mouth and other appendages to scratch at food sources, breaking them up into smaller pieces for consumption.
Some crabs will filter feed using small, thin setae (hair-like protrusions) located in the mouth.
Setae can be found on other parts of the body as well, connected to the crab’s nervous system, providing many functions to the crab.
These setae allow them to not only filter and obtain food particles in the water but allow them to detect movements of nearby prey or predators.
Some crabs eat dirt or sand, using their mouths to scrape it off of a food source. The sand and mud form into compacted pellets that are then ejected from the crab’s mouth.
Hermit crabs (Paguroidea), in particular, will consume their own feces for the protein and minerals in them, such as calcium for a strong exoskeleton.
In general, if the food source is edible, and fits into its mouth, then it will consume it.
Eating If Injured
Crabs have poor eyesight, especially in deep and murky waters, and thus rely on their claws and setae. They can regrow injured or shed limbs.
If a crab cannot feed in a normal fashion due to injury or while waiting for a limb to grow, they will typically forage and eat carcasses. A crab will stretch its body out, lowering its mouth to the substrate to obtain food.
Crabs are versatile eaters, consuming shrimp, fish, plant materials, and more.
They obtain food by using chemoreceptors, sensitive hair-like setae, foraging, predatory behaviors, and more. Larger crabs with strong pincers can access hard-textured and larger food sources.
Crabs consume considerable amounts of food daily in small quantities to support exoskeleton growth.