Are Lobsters Cannibals? (Why?)

Lobsters’ diet was a mystery for us years ago as we thought they only eat dead particles of other animals. With more studies, we found out that they eat a variety of fresh food instead. A few years ago, we even conducted studies on lobsters’ cannibalism, and what are the results? If you wonder if lobsters are cannibals, in this article, we’ll talk all about that. However, let’s begin with a quick answer:

Lobsters are cannibals, meaning that sometimes lobsters eat other lobsters. The factors causing their cannibalism are rising water temperatures and their rapid increase and reproduction, overfishing, the availability of alternative prey, and critical nutrition in other lobsters.

However, this certainly doesn’t tell the whole story. Below I’ll explain more about lobsters being cannibals, why they’re cannibals and if other crustaceans also engage in this behavior. Furthermore, I’ll explain more about what lobsters eat. Read on!

Are lobsters cannibals?

Many years ago, we thought lobsters were only scavengers, meaning they ate primarily dead things. However, we discovered they eat diverse fresh food, including crabs, shrimps, fish, and more. Lately, we even found that lobsters eat other lobsters as well!

Furthermore, lobsters might be even bigger predators for juvenile lobsters (in some regions) than fish – according to the scientist Noah Oppenheim from Maine. During the summer of 2012, when lobsters exploded in number along the Maine coast, he conducted research on their cannibalism.

We knew that lobsters would eat other lobsters in captivity, but we were sure if they would show the same behavior in the wild. To figure this out, Oppenheim tied a small, juvenile lobster to the base of an infrared camera, left it on a table about 20 feet (6 meters) underwater, and waited for what would happen.

What happened at night was proof of lobsters’ cannibalism. The adult lobster came, grabbed a juvenile in less than a second, tore the claw off, and consumed it. As Oppenheim says, “It’s very gruesome, but this a process that is occurring out in the wild every night”.

Why do lobsters eat each other?

Lobsters eat each because of warming waters due the climate change, overfishing, and because they’re a source of important nutrients.

Warming waters

As the water temperature elevates, lobsters reproduce more frequently with larger broods, and they grow more rapidly. Oppenheim thinks cannibalism is a direct effect of their overly high densities along the Maine coast.

Lobsters are known for their territory fights after which the winner has the privilege of the best shelters and preferential mating rights. Right now, when lobsters encounter themselves so frequently, it may result in more than just a bit of competition in a predator-prey interaction.

In addition to that, high temperatures can also bring diseases and not sustainable habitat for lobsters. For instance, in 1998, in Long Island Sound, every lobster disappeared, which was either caused by the diseases or the high temperatures that made them move away.

Overfishing

Another reason why lobsters started eating each other is overfishing. Because of overfishing, the number of lobster predators, like cod, decreased. This causes their population to bloom and, again, it results in encountering themselves much more frequently.

Overfishing bigger fish also means fish reproduction is decreased. Therefore, a reduced amount of smaller fish compels lobsters to change their diet as fish are one of the lobsters’ favorite food.

Nutrition

After molting, lobsters’ new shell is soft, and they need to harden them quickly to protect themselves from predators. They require nutrition to do that, which they can get from the old shell that they sometimes eat after molting. This means they provide important nutrients by eating other lobsters as well.

Do other crustaceans eat each other as well?

But is it normal that lobsters eat each other, and do other animals do that too? Interestingly, cannibalism in crustaceans is not so unusual. Not even only in crustaceans but in other marine animals, such as sea stars, sea urchins, fish, sharks, squid, and more.

One of the factors why crustaceans are particularly likely to engage in cannibalism is because they shed their shells in a process called molting. This process is energetically expensive, and cannibalism may provide critical nutrition. Even after the molting, crustaceans usually will eat their old shell to receive the nutrition necessary to harden their shells faster – making them more resistant to predators.

Read more about molting in lobsters in my other article: “How Often Do Lobsters Molt?”.

Other factors of cannibalism in crustaceans are many environmental factors, such as habitat type, complexity, and the availability of refugia. Others are the availability of alternative prey and the size structure of populations.

What else do lobsters eat?

As I mentioned at the beginning, we used to think lobsters are only scavengers, so it’s interesting to know what we found out about their diet. Lobsters will still consume decaying organic matter, but primarily they eat fresh food, such as shrimps, crabs, and other crustaceans, fish, sea urchins, worms, algae, mollusks, and carrion meat.

Shrimps

Shrimp are the primary food source for lobsters, especially in the Caribbean. Shrimps also belong to crustaceans and also live on the bottom of the ocean, which makes it very accessible for hungry lobsters.

Crabs and other crustaceans

Lobsters will also prey on crabs and other crustaceans, such as prawns, krill, barnacles, and crayfish. Eating other hard-shell animals is especially easy for clawed American lobsters with huge claws that help them to crash food.

Fish

Lobsters eat fish, and to catch them, they would sit and wait for little fish to pass by. When the time is right, they’ll catch them with their claws rapidly.

Sea Urchins

Sea urchins are very nutritious for lobsters. Sea urchins’ spines and hard shells protect them from predators, but for lobsters, that’s not a problem. They can easily turn sea urchins upside down, exposing the soft bodies that are usually hidden underneath them.

Worms

Lobsters will also eat a wide variety of marine worms, such as roundworms, flatworms, arrow worms, and horseshoe worms. Worms also live on the ocean floor, so it’s easy for lobsters to catch them while they’re passing by.

Algae

Nutritious algae often grow close by, so lobsters also consume them and other plants. There’s a wide variety of algae growing on the sea bed, and lobsters consume them all.

Mollusks

Mollusks are also on the lobster menu. They’re many different species of mollusks, including snails, slugs, mussels, oysters, and octopuses. Many species are very slow, so it’s easy prey for quick and strong lobsters.

Carrion meat

Carrion meat is an animal’s dead, decaying matter that usually floats around in the ocean. Lobsters will catch it with their appendages when the food it’s drifting around on the bottom or in the water.

Sources

• Bleakley, Bronwyn, ‘Cannibalism in Crustaceans’, in Martin Thiel, and Gary A. Wellborn (eds), Life Histories: Volume 5 (New York, 2018; online edn, Oxford Academic, 23 Sept. 2021), https://doi.org/10.1093/oso/9780190620271.003.0014, accessed 11 Sept. 2022.