What creature has the best and most adaptable eyesight in the natural world, packs a wicked punch harder than a bullet and can change its body colors at will?
This would be the mantis shrimp in the stomatopod family!
Remember the baby alien creature in the movie “Alien” that suddenly hatches out of its victim’s stomach? The mantis shrimp reminds me of that explosive moment, one of the scariest in any movie I’ve seen. But this astonishing little creature is even more real, though it’s neither a mantis nor a shrimp, despite its name. It actually departed from the shrimp family hundreds of millions of years ago.
Mantis shrimps are beautiful and vibrant in color, but deadly, able to club prey with the force of a bullet or spike them with sharp claws. They are true killing machines, with an ability to smash or skewer their prey unique in the natural world.
This creature also has one of the most sensitive visual systems in nature. Furthermore, most mantis shrimp species are monogamous, some pairs staying together for as long as 20 years! For these species, males care for their female mate’s eggs by tending part of their egg clutch in a separate nest, or by foraging for food to bring to their nesting mate. This small beastie combines ferocity, unique visual acuity, and a loving adherence to a loyal partnership. What an amazing combination! And after all, with these combat skills, fights between spouses could get destructive…
One unique crustacean
Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda (from Ancient Greek στόμα (stóma) ‘mouth’, and ποδός (podós) ‘foot’). Stomatopods branched off from other members of the crustacean class around 340 million years ago, and developed their own unique characteristics. Unlike most crustaceans, they often hunt, chase, and kill prey.
Called “sea locusts” by ancient Assyrians, “prawn killers” in Australia, and now sometimes referred to as “thumb splitters” – because of the animal’s ability to inflict painful wounds if handled incautiously – mantis shrimp have powerful raptorials that are used to attack and kill their prey either by spearing, stunning, or dismembering it. Some mantis shrimp species have specialized calcified “clubs” that can strike with great power, while others have sharp forelimbs used to seize the prey (hence the term “mantis” in its common name). So if you pick one up, do so very carefully or it might break your finger!
Mantis shrimp have used their unique punching abilities to shatter the glass walls of an aquarium, much to owners’ surprise and dismay. They have also been known to attack their own reflection through the glass, calling for a use of specially heavy glass in aquariums built to hold these pugnacious captives.
There are around 450 species of mantis shrimp worldwide, and their colors range from shades of brown to bright, green, red and blue. The best-known species is the Peacock mantis shrimp (also known as harlequin mantis shrimp, painted mantis shrimp, or clown mantis shrimp), which is one of the larger, more colorful mantis shrimps commonly seen. They typically grow to around 2-10 inches (5-25 cm) in length, but some were recorded to be as large as 18 inches (46 cm) long.
The mantis shrimp has a flattened, translucent body with a pale green hue. Its abdomen and carapace (or shell) are segmented, with each segment outlined in dark green or yellow. It has three pairs of walking legs, four pairs of clawed appendages and one pair of long, jackknife claws that resemble a praying mantis. Its emerald green eyes are on stalks located on the top of its head.
While relatively common, mantis shrimp are not well-understood because they are solitary and territorial sea creatures, spending most of their time hiding in rocks and burrowing in the seabed, most commonly in U-shaped burrows at the base of coral reefs. Depending on the species, they can be active during the day or entirely nocturnal. Since these sea creatures rarely exit their homes except to feed and relocate, they are rarely seen by humans. Shy guys, I guess!
Mantis shrimp are skilled predators, and their diet depends on the species. They typically eat fish, crabs, clams, snails, worms, shrimp and squid. They can also prey on animals much larger than themselves due to their significant punching power.
Though some live in temperate seas, most mantis shrimp live in tropical and subtropical waters in the Indian and Pacific Oceans between eastern Africa and Hawaii. The two main categories of mantis shrimp – spearing and smashing – favor different locations for burrowing. The spearing species build their habitat in soft sediments and the smashing species make burrows in hard substrata or coral cavities.
These two habitats are crucial for their ecology since they use burrows as sites for retreat and as locations for consuming their prey. Burrows and coral cavities are also used for mating and keeping eggs safe. Stomatopod body size undergoes periodic growth which necessitates finding a new cavity or burrow that will fit the animal’s new diameter. Some spearing species can modify their pre-established habitat if the burrow is made of silt or mud, which can be expanded.
Both brawn and brain
The mantis shrimp is highly intelligent, with complex social behavior and ritualized fighting and protective activities. With a great capacity to learn and retain knowledge, mantis shrimp can recognize and interact with fellow mantis shrimp through visual signs and even by individual smell. Their eyes are considered the most complex in the animal kingdom, with great color and depth perception, as well as polarization sensitivity, making these creatures’ brains far more efficient than virtually any other species in nature.
Although stomatopods typically display the standard types of movement seen in true shrimp and lobsters, one species can flip itself into a crude wheel. Most mantis shrimps live in shallow, sandy areas, and at low tides, they can be stranded by their short rear legs. While those might be sufficient for movement when the body is suspended in water, they’re not up to the task when the mantis shrimp finds itself on dry land. In these situations, mantis shrimp perform will a forward flip in an attempt to roll into the next tide pool, and they’re capable of moving up to two meters (over 6 feet) in this manner.
The mantis shrimp’s second pair of thoracic appendages has been highly adapted for powerful close-range combat. The appendage differences divide mantis shrimp into two main types: those that hunt by impaling their prey with spear-like structures and those that smash prey with a powerful blow from a heavily mineralized club-like appendage. A considerable amount of damage can be inflicted after impact with these robust, hammer-like claws.
Both types strike by rapidly unfolding and swinging their claws at the prey, and can inflict serious damage on victims significantly greater in size than themselves. In smashers, these two weapons are employed with blinding quickness, with an acceleration of 10,400 g (102,000 m/s2 or 335,000 ft/s2) and speeds of 23 m/s (83 km/h; 51 mph) from a standing start, which is somewhat “faster than a speeding [.22] bullet” fired out of a gun (a Superman reference, for you youngsters out there!).
Because these mantis shrimp strike so rapidly, they generate vapor-filled bubbles in the water between the appendage and the striking surface – known as cavitation bubbles, which are super-heated bubbles with a small flash of light which for split seconds also generates temperatures of 4,400 degrees Celsius in the surrounding water (which is nearly as hot as the sun).
The collapse of these cavitation bubbles produces measurable forces on their prey in addition to the instantaneous forces of 1,500 Newtons caused by the impact of the appendage against the striking surface, so the prey is hit twice by a single strike: first by the claw and then by the collapsing cavitation bubbles. Even if the initial strike misses the prey, the resulting shock wave can be enough to stun or kill.
Smashers use this ability to attack crabs, snails, rock oysters, and other mollusks, their blunt clubs enabling them to crack the shells of their prey into pieces. Spearers, however, prefer the meat of softer animals, such as fish, which their barbed claws can more easily slice and snag. Check out a peacock mantis shrimp’s skills on video:
The eyes of the mantis shrimp are mounted on mobile stalks and can move independently of each other. They are thought to have the most complex eyes and front-end for any visual system in the natural kingdom. Compared with the three types of photoreceptor cells that humans possess in their eyes, the eyes of a mantis shrimp have between 12 and 16 types of photoreceptor cells.
Furthermore, some species of these mantis shrimp can tune the sensitivity of their long-wavelength color vision to adapt to their environment. This phenomenon, called “spectral tuning”, is species-specific. Despite the impressive range of wavelengths that mantis shrimp can see, they do not have the ability to discriminate between closely positioned wavelengths, which may allow these organisms to assess their surroundings with little delay, reflecting their territoriality and combativeness.
Each compound eye is made up of tens of thousands of clusters of photoreceptor cells, consisting of two flattened hemispheres that divide the eye into three regions, which enable mantis shrimp to see objects with trinocular vision, giving them great depth perception. Mantis shrimp can perceive wavelengths of light ranging from deep ultraviolet (300 nm) to far-red (720 nm) as well as polarized light. They are not believed to be sensitive to infrared light.
The mantis shrimp’s capacity to see UV light may enable observation of otherwise hard-to-detect prey on coral reefs. Some species of mantis shrimp are reported to detect circularly polarized light, which has not been documented in any other animal; this could inspire new types of optical media that might outperform our current Blu-ray Disc technology. They also have a structure in their eyes that is much like the technology found in DVD players, only far more advanced.
Researchers from the University of Queensland believe that the compound eyes of mantis shrimp can detect cancer lesions and the activity of neurons, because polarized light reflects differently from cancerous and healthy tissue before appearing as visible tumors. This capability has inspired a group of researchers to build a proof-of-concept camera sensor, inspired by the mantis shrimp’s visual acuity. So this species is helping doctors too!
One subspecies of mantis shrimp is the only animal known to have vision with optimal dynamic polarization, achieved by rotational eye movements to maximize the contrast between the object in focus and its background. Since each eye moves independently from the other, it creates two separate streams of visual information.
By moving their eyes to scan their surroundings, mantis shrimp can add information about forms, shapes, and landscape that cannot be detected just by their eyes’ upper and lower hemispheres. They can also track moving objects using large, rapid, and independent eye movements, allowing their eyes to cover a very wide visual field.
The wide diversity of mantis shrimp photoreceptors likely comes from ancient gene duplication events. Over the years, some species have lost the ancestral phenotype, although some maintain 16 distinct photoreceptors and four light filters. Species in a variety of visual environments have very high selective pressure for photoreceptor diversity and maintain ancestral phenotypes better than species that live in murky waters or are primarily nocturnal.
The eyes of mantis shrimps may enable them to recognize different types of coral, prey species (which are often transparent or semitransparent) or predators, such as barracuda, which have shimmering scales. Alternatively, the way they hunt with very rapid movements of their claws may require extremely accurate ranging information, which would require excellent depth perception. So maybe the rest of us should steer clear!
Researchers suspect that the broader variety of photoreceptors in the eyes of mantis shrimps allows visual information to be preprocessed by the eyes instead of the brain, because the brain would otherwise have to be larger to process all that input. The mantis shrimp uses the different types of photoreceptors in its eyes to perform the same function as humans’ brain neurons, resulting in a hardwired and more efficient system for an animal that requires rapid color identification. Humans have fewer types of photoreceptors, but more color-tuned neurons, while mantis shrimp appear to have fewer color neurons and more diverse classes of photoreceptors.
Mantis shrimps can have as many as 20 or 30 breeding episodes over a lifetime. Depending on the species, eggs can be laid and kept in a burrow, or are carried around under the female’s tail until they hatch. Also depending on the species, males and females may come together only to mate, or they may bond in monogamous, long-term relationships.
In the monogamous species, mantis shrimps remain with the same partner for up to 20 years. They share the same burrow and may even coordinate their activities. Both sexes often take care of the eggs, in a phenomenon known as bi-parental care. In some species, the female lays two clutches of eggs – one that the male tends and one the female tends. In other species, the female looks after the eggs while the male hunts for food. After the eggs hatch, the offspring may spend up to three months as plankton.
During mating rituals, mantis shrimps actively fluoresce, and the wavelength of this fluorescence matches the wavelengths detected by their eye pigments. Females are only fertile during certain phases of the tidal cycle; the ability to perceive the phase of the moon may, therefore, help prevent wasted mating efforts. It may also give these shrimps information about the size of the tide, which is important to species living in shallow water near the shore.
The exact advantage of this creature’s visual sensitivity to polarization remains unclear; however, polarization vision is used by other animals for sexual signaling and secret communication that avoids the attention of predators. This mechanism could thus provide an evolutionary advantage; it only requires small changes to the cell in the eye and could be supported by natural selection.
With its super strength, vision, memory, and combat skills, the mantis shrimp is an amazingly capable creature!
Time to punch out now.
By Fred Jennings