There is a rich biodiversity among crabs, with over 4500 unique species identified, ranging from blue crabs and king crabs to Dungeness crabs, hermit crabs, and snow crabs, among others. These crustaceans use their elongated arms, equipped with claws, as effective tools for securing food. So, what do crabs eat?
Contrary to what one might expect, crabs aren't particularly picky eaters. Most crabs favor a diet of fish, worms, shrimps, crustaceans, snails, and small animals. Nevertheless, others lean towards a predominantly plant-based diet. Overall, crabs are partial to various food options, leading to a primarily omnivorous dietary classification.
Let's dive deeper into understanding the crab's dietary preferences and hunting methods. And if you want to know how diverse they are, check out our article about types of crabs.
What to know about crabs
You will find crabs all over the world in oceans, fresh waters, and marine waters. Crabs live in areas close to the sea and also live on land.
The crab’s body is covered with an exoskeleton made of chitin. They have five pairs of legs (8 walking legs) and two pincers or chelae (claw-like organs) at the end of their front limbs. Some crab species can swim and use their hind legs as paddles.
Crabs come in various sizes, with smaller crabs like the pea crab and larger crabs like the Japanese spider crab.
Crabs have chemoreceptors that help them detect chemicals released in water by their prey1. You can find most of these receptors on the crab’s antenna. Receptors near the crab’s eyes allow it to examine the environment, while receptors on its mouth work as food tasters.
During mating season, both male and female crabs work to find the perfect location to lay their eggs. As they grow and mature, crabs shed severally, shedding off the old shell and growing a new exoskeleton2.
Related Read: Crab Facts.
A crab's diet
What do crabs eat after a long day walking along the coastlines and swimming in the oceans? Crab diets vary depending on where they live. Let’s look at some foods that these crustaceans eat:
Small fish make up a good percentage of the foods that crabs eat. Crabs like fiddler crabs, hermit crabs, and other crabs look for these small fishes on the ocean floor. Because a fish typically moves faster than a crab, crabs prefer to feed on an injured or dead fish. They also eat fish eggs.
Some crabs, like king, snow, and blue crabs, eat crustaceans like crayfish, barnacles, lobsters, and even other crabs.
Squid & whelks
The larger crabs, like Dungeness crabs, may feed on larger animals like squid and whelks. These scavengers move along the ocean floor, looking for animals like squid and whelks buried in the sand.
They may even use their large claws to catch a passing squid. However, this could be challenging for the Dungeness crab, so they will typically feed on dead squids.
Seaweed & Algae
One typical non-meat diet that most crabs eat is seaweed and algae. Crabs feed on both green algae and red algae, which can be found in freshwater and saltwater environments.
Crabs such as the fiddler crab, hermit crab, and many other crab species pick up algae from rocks using their claws to cut or scrape it.
Shrimps & prawns
Crabs like to eat shrimp and prawns. Shrimp and prawns contain many nutrients like fats, protein, and calcium. Some common species of crabs that feed on shrimp are hermit crabs, red rock crabs, giant coconut crabs, and so on.
Small clams & mussels
Bigger crabs, like king crabs, eat clams and mussels. Small clams and mussels contain nutrients like vitamins. Crabs rely on their sense of smell and taste while moving across the ocean floor to prey on small clams and mussels.
Crabs are a common predator of the sea urchin. Many species of crabs, including the Dungeness crabs, rock crabs, and king crabs, may feed on sea urchin species like sand dollars. These crabs use their claws to crack the sea urchin shells to eat the soft tissue on the inside.
Decaying animal matter like dead shrimp is an essential and common crab meal. Crabs do not hunt so well, given their slow pace and eyesight. So, crabs are scavengers and will typically eat dead animals instead of hunting for living animals.
What do crab species kept in captivity eat?
Crabs in the natural environment demonstrate a diverse palate, consuming various foods ranging from shrimp and fish to deceased organisms. The dietary regime of captive crabs, however, differs in several aspects.
Typically, people maintaining captive crabs provide them with a diet of flakes and pellets. These comprise essential nutrients vital for the crabs' health. Additionally, plant-based foods like seaweed and algae form a significant part of a captive crab's diet.
They add fruits and vegetables packed with essential vitamins and minerals to boost the nutritional content of a crab's diet. Furthermore, captive crabs can benefit from a protein-rich diet by adding live or frozen foods in addition to seafood like shrimp and shellfish.
What do crabs eat while on land?
Crabs are uniquely versatile eaters, thriving both in water and on land due to their mouth-watering omnivorous diet. A crab's diet on land primarily involves fruits, vegetables, worms, insects, and decaying plants.
Moreover, when it comes to a meat diet, crabs indulge in mollusks such as snails and slugs. Therefore, it is clear that crabs are highly adaptable in their food habits, making the most of available resources across diverse environments.
What do baby crabs eat?
If you're taking care of a baby crab, you might be curious about their diet. It's worth noting that their diet closely mirrors that of an adult crab - both are omnivores that consume a balance of animal and plant matter.
Therefore, juvenile pet crabs can consume shrimp, small fish, plankton, meat, peas, apples, and kale, among other things. You can also incorporate flakes and pellets into their diet to give them all the nutrients for good health.
How do crabs hunt and collect food?
Crabs, unique in their hunting methods, primarily use chemoreceptors as a sensing mechanism due to their lackluster vision. These chemoreceptors allow them to detect the chemical emissions from potential prey, making them effective hunters even with visual constraints.
Bigger crabs, like the king crab, catch their prey using their formidable claws. They also utilize these tools to crush their victims. Interestingly, some crabs even prey on other, smaller species of their own kind, showing a broad diet spectrum in these creatures.
Aside from their predatory nature, crabs also play a role as scavengers, using their claws as filtering mechanisms. They sieve through sand and soil for remnants of dead or decaying lifeforms, both animal and plant. Crabs utilize their claws to convey the food to their mouths when they have located a food source.
How much food does a crab eat?
Crabs will eat when their punchers lay hold of food. However, crabs don’t have teeth and so cannot take a large bite or eat large amounts of food.
Don’t worry. Crabs can do well with eating every day. This is especially important for baby crabs. Young crabs require frequent feeding to aid growth and development.
Because of their anatomy, crabs will find it challenging to break down food in their mouth. When feeding your crab, tearing up foods into small pieces can be very beneficial to them.
What to not feed pet crabs?
Crabs are not picky, but if you have a pet crab, you need to be careful not to feed them some types of food. Here are some food items you should avoid when feeding crabs:
- Table salt: The table salt in your kitchen cupboard contains high amounts of iodine. While small amounts of iodine are healthy for crabs, large amounts can be toxic to them. So, if you’re mixing salt and water, you want to avoid your table salt.
- Onion and garlic: Onion and garlic are unacceptable for crabs as they could be toxic.
- Citrus fruits: Citrus fruits like lemons and oranges are not exactly toxic to crabs, but some crabs may not eat them because of their strong scent.
- Rotten or moldy foods: While crabs will likely feed on dead food in the wild, you want to avoid feeding your crab moldy or spoiled food as this can be unsafe for them.
- Pesticides and herbicides: Pesticides and herbicides can be toxic for crabs. So, you want to ensure you’re buying and feeding your crab with only fresh organic food.
- Cocoa or chocolate: Chocolates contain lots of sugar and chemicals that may be toxic to crabs.
Related read: Crab Quotes.
What feeds on crabs?
If you’ve ever had a plate of delicious crab legs, then you know that humans eat crabs. Some popular edible crabs that humans eat include blue crabs, king crabs, stone crabs, soft-shell crabs, and more.
Smaller crabs may also have natural predators in the wild. For example, fish-eating birds like the great blue heron (see picture above) and other larger fish may eat crabs.
Crabs exhibit flexibility in their dietary habits, consuming various animal- and plant-based foods. Their omnivorous nature allows them to leverage diverse food resources depending on their habitat.
Should you care for a pet crab, ensuring a diet enriched with vital nutrients is vital, shunning certain food categories as discussed in this piece.
Aggio, J. F., Tieu, R., Wei, A., & Derby, C. D. (2012b). Oesophageal chemoreceptors of blue crabs,Callinectes sapidus, sense chemical deterrents and can block ingestion of food. The Journal of Experimental Biology, 215(10), 1700–1710.
Alaska Fisheries Science Center (February 2022). Alaska Shellfish Growth Research. NOAA.