What Do Crustaceans Eat?

Hermit crab
iStock.com/chameleonseye

Written by Volia Schubiger

Published: October 5, 2022

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What is the first thing that comes to mind when you think of crustaceans? Are you picturing a crab walking sideways along the beach? Or maybe you picture those giant fish tanks with lobsters inside. However, did you know that crustaceans actually include a wider range of animals than just crabs? A variety of animals make up the crustacean family, and they are all extremely important to the ecosystem. Are you curious to learn more about these amazingly diverse species? Let’s take a close look into what crustaceans eat, as well as other fun facts about them!

What Are Crustaceans?

woodlouse crawling on a stone

As terrestrial crustaceans, woodlice are more closely related to crabs and shrimps than insects.

Crustaceans – what are they? Let’s start from the beginning. A crustacean is classified as an arthropod. In other words, their skeletons are on the outside of their bodies. In terms of diversity, crustaceans are the most diverse group of arthropods, and they rank second or third in number after insects and vertebrates. The majority of crustaceans live in the sea, including lobsters and crabs. On land, there are two types – Rolie polies and crayfish. Their habitats range from the Arctic to the Antarctic, as well as elevations in the Himalayas up to 16,000 feet and below sea level. 

A crustacean’s hard exoskeleton provides protection from predators and keeps it from losing water. The exoskeletons of crustaceans, however, do not grow as the animals inside them do, so as they grow bigger, they must molt. Your mind might be picturing hermit crabs walking around with their “homes” on their backs until they outgrow them. In that case, you’d be right. In most cases, crustaceans expand their body size by 40 percent to 80 percent right after molting to fit into their new exoskeleton.

Now that we have a better idea of what a crustacean is let’s look at what crustaceans eat.

What Do Crustaceans Eat?

Animals With Exoskeletons-European Lobster

There are two types of claws on lobsters, a crusher claw and a pincher claw.

Crustaceans eat a diet that consists of microscopic organisms, algae, plankton, snails, plants, and even eggs of other marine life. They are classified as omnivores. Nevertheless, crustaceans have a wide variety of eating habits among their numerous species. 

In most cases, crustaceans are omnivorous scavengers whose primary function is to clean the ocean surface. Their primary food source is organic matter left behind by larger predators, which they consume by swimming or crawling around.

In some cases, crustaceans are not even capable of swimming around to feed. A barnacle will stay stationary on a reef and use its hairy legs to filter any zooplankton or phytoplankton passing under it. Also, because crustaceans and Nauplius larvae are sometimes found in zooplankton, these scavengers are effectively eating other crustaceans.

It is common for large crabs and lobsters, which are predatory crustaceans, to hunt and eat other large crustaceans they can catch. As a result of its weakening state and soft exoskeleton shell, molting crustaceans are particularly vulnerable to being eaten by another of their own kind during this time. Crabs and other crustaceans also feed on all kinds of prey with their pincers, including sea urchins, clams, mussels, snails, worms, countless fish, and clams. 

Complete List of What Crustaceans Eat 

Because crustaceans come in so many varieties, their diet will be extremely diverse. As we mentioned above, some are primarily scavengers that eat whatever they can find. Others are predators that even prey upon weaker crustaceans that are currently molting. 

A crustacean’s full diet includes the following: 

  • Small fish
  • Seaweed 
  • Algae 
  • Plankton 
  • Plants 
  • Snails 
  • Shrimp, prawn, and krill 
  • Dead animals 
  • Worms 
  • Clams 
  • Mussels 
  • Sea urchins 

The crustacean diet is incredibly diverse, as you can see. Each crustacean species eats something on this list, even though not all species eat everything on it. After learning what crustaceans eat, let’s take a look at how they find their food.

How Do Crustaceans Hunt & Forage For Food?

Largest Crabs - Japanese Spider Crab

Crabs use their sense of smell to detect prey and their pincers to help grasp them and break down food.

The diversity of crustaceans makes it natural for them to have many unique methods of obtaining food. As for how crustaceans obtain food, they either prey on prey, filter feed on prey, scavenge for food or parasitize on other creatures. The majority of crustaceans can move around as they please, but there are some stationary species, like barnacles, that can’t move. There is no doubt that this impacts how they get their food.

The barnacle is a filter feeder or suspension feeder. Their method of eating involves sweeping food into their mouths from the water, and food is eaten with their feet. In contrast, rolly pollies find food using their sense of smell. If you were to ask a rolly polly what it would eat in the wild, they would probably say pretty much anything decaying. It includes not only plant matter but also animal matter as well.

Next, we have the predatory crustaceans. Crabs and lobsters find prey using their sense of smell, like many other marine animals. Also, their claws enable them to manipulate the food and break them into smaller pieces so they can easily swallow them. They use their strong claws to break through the shells of other sea life to catch various types of prey.

There are almost as many types of crustacean diets as there are crustaceans themselves, as you can see. However, most species are omnivorous scavengers that will happily consume any food dangled in front of their pincers and mandibles. 

What Eats Crustaceans In The Wild?

Since crustaceans can be found in many different habitats, almost all carnivores eat them. Around the world, crustaceans live in virtually every type of environment. Crustaceans living at the bottom of the ocean are often preyed on by bottom-feeding fish, octopi, and larger fish and marine mammals. Many carnivorous reptiles eat crustaceans, including alligators, crocodiles, and snakes.

It’s important to note, however, that marine life is not the only predator of crustaceans. Crustaceans are also eaten by sea birds. To break open hard-shelled crustaceans, birds drop them from heights. The majority of mammals eat crustaceans as well. As far as land animals are concerned, apes, monkeys, raccoons, seals, and sea lions all prey on crustaceans regularly. Lastly, humans are avid consumers of several species of crustaceans, notably crabs, lobsters, and shrimps.

It is considered a delicacy to eat crabs because of the muscle in their pincers and legs and to eat lobsters because of their significantly muscular tails. Many Americans, especially those in the country’s southern part, consider crayfish a delicacy since it is a freshwater crustacean. There is no doubt that crustaceans are incredibly important to the ecosystem. In addition to serving as water cleaners, they also serve as food sources for other animals. 

A study published in 2017 revealed that large plant-eating dinosaurs from the Late Cretaceous may have even been able to consume crustaceans. According to fossil evidence, herbivorous dinosaur diets were relatively flexible, making them comparable to extant herbivorous birds.

What To Feed Pet Crustaceans

The keeping of crustaceans as pets is very common in aquariums. Keeping freshwater crabs and shrimp in aquariums can help keep them clean and help maintain a healthy environment. Fiddler crabs are a popular option thanks to their living requirements. Generally, fiddler crabs live in terrariums that have sand, plants, and water to live in. In terms of crustaceans, hermit crabs are one of the most popular pets. An environment with a lot of moisture and sand is ideal for him. The shells of hermit crabs vary in color and shape according to what they have gathered from their habitat.

A pellet food diet that includes vegetables and fruits is recommended for hermit crabs. In order to keep shrimp, crabs, and lobsters alive, you have to feed them pellets that sink to the bottom. They also prefer a variety of frozen brine shrimp, bloodworms, and tubifex worms. Pet crayfish will also consume sinkable pellets as well as vegetables such as zucchini and carrots. Crustaceans make excellent pets because they don’t have picky eating habits, which makes keeping them as a pet so easy and enjoyable.


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About the Author

Volia Schubiger is a freelance copywriter and content editor with a passion and expertise in content creation, branding, and marketing. She has a background in Broadcast Journalism & Political Science from CUNY Brooklyn College. When she's not writing she loves traveling, perusing used book stores, and hanging out with her other half.

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