Mantis shrimp: The crustacean that packs a punch

Armed with kaleidoscopic eyesight, the ability to send secret messages and a punch so fast it can boil water, mantis shrimps are a force to be reckoned with.

What is a mantis shrimp?

With a hard exoskeleton and hinged forearms, mantis shrimps get their common name from their resemblance to both a shrimp and a praying mantis. However, they’re actually neither of these.

Instead, mantis shrimps belong to an ancient order of crustaceans called Stomatopoda. This group branched off from the Malacostraca class – which includes crustaceans such as crabs and lobsters – about 400 million years ago. This makes stomatopods much older than dinosaurs!

We find mantis shrimps in the warm, shallow waters of the Pacific and Indian Oceans. They live in burrows that they dig with their strong front limbs. These burrows are used as hunting bases, protective shelters and nurseries where females guard their eggs.

Most mantis shrimps spend the majority of their lives inside these shelters, venturing out only to hunt or to move into larger burrows as they grow.

Depending on the species, mantis shrimps may live in their burrows alone or in pairs. Some form lifelong monogamous bonds with a single mate.

The females carry their eggs attached to their stomach, aerating and cleaning them. The number of eggs varies depending on the species, but some, like the peacock mantis shrimp, can carry around 50,000 per clutch.

After the eggs have hatched, the larvae become plankton – tiny organisms that float about in the water, carried by the ocean currents. They float on the surface of the water for days or weeks, before coming down to the ocean bed.

There are more than 400 species of mantis shrimps and they’re incredibly diverse in appearance and size. Most adults are between around two and 10 centimetres long. However, adults of some species can be much larger. For example, the zebra mantis shrimp, which is named for its distinctive brown and cream stripes, can reach up to 40 centimetres in length.

Perhaps the most well-known species is the peacock mantis shrimp. It’s also known as the harlequin or painted mantis shrimp because of its vividly coloured exoskeleton. Scientists think that their shells reflect light frequencies that only they can see. This lets them communicate with each other to send warning messages of territory or mating signals. This species ranges in size from about 3-18 centimetres.

How hard can a mantis shrimp punch?

Mantis shrimps have two forelimbs called raptorial appendages. Many arthropods have raptorial appendages, but mantis shrimps have an extra part attached to theirs called a dactyl club.

Mantis shrimps use their dactyl clubs to deal out strong punches while hunting for food, in self-defence and in fights with other mantis shrimps. They keep their dactyl club tucked away using a spring and latch mechanism. In this position, it stores up huge amounts of energy, meaning they can release their club with extreme force.

We can divide mantis shrimps into two groups – smashers and spearers.

Spearers, such as the zebra and tiger mantis shrimps, have a sharp dactyl club covered in barbed spines. They lie in wait, hidden in their burrows, and then strike, impaling soft-bodied prey such as fish and squid.

Smashers, such as the peacock mantis shrimp, have a specialised hammer-like dactyl club. They use this to bludgeon hard-shelled prey, including crabs, snails and molluscs. Smashers tend to be more active hunters. Their strike is incredibly powerful. They can hit prey at speeds of around 23 metres per second, which is about as fast as a bullet fires from a gun. That’s around 50 times faster than you blink.

However, the power of their strike lies in more than just its speed or force. When a mantis shrimp releases its dactyl club, the water between the object and the club vaporises. This creates cavitation bubbles – tiny vapour pockets that collapse with explosive energy. As these bubbles implode, they produce heat, boiling water and even flashes of light. So, even if the mantis shrimp’s punch misses, the crustacean can still deliver a lethal shockwave that stuns or kills nearby prey. The force is so immense that mantis shrimps have been known to crack, and sometimes even shatter, the glass walls of aquarium tanks.

Why doesn’t a mantis shrimp harm itself when it punches?

Despite striking at incredible speeds, mantis shrimps don’t cause any harm to themselves. This is thanks to the unique structure of the dactyl club, which is made up of a complex, multi-layered material. Inside, tiny fibres are arranged in a spiral pattern that helps absorb and disperse the force of impact.

This prevents damage to the club too and has even caught the attention of scientists who are studying new ways to create advanced armour and protective materials.

How good is the eyesight of a mantis shrimp?

Mantis shrimps have extraordinary eyes. In our eyes, we have three types of photoreceptors – the cells in the retinas that can detect light. These are tuned to red, blue and green light waves. Mantis shrimps have about 12 types of photoreceptors, with some species having as many as 16, meaning they have more than any other animal. As a result, they can see a huge array of colours and even detect ultraviolet and polarised light that’s invisible to us.

Mantis shrimps’ two eyes, which are perched on stalks on their heads, can also move independently and detect the distance of an object with a single eye. They’re even able to apply filters that tune the cells of their eyes to adapt in different lighting conditions, which allows them to detect predators and prey.

So, if you ever spot one of these harmless-looking, colourful crustaceans, take a moment to think about the extreme force hiding behind its small body.