Mantis Shrimp in Australia: Are They Dangerous?

Hover over a sandy patch between coral heads on a tropical reef and something may be watching you back. Two eyes on stalks swivel independently, rarely pointing the same way, above a body painted in greens and electric blues. Lean in for a closer look and the animal is gone, scooting back into its hole before you can raise a camera.

Mantis shrimps are exclusively marine, predatory crustaceans (order Stomatopoda), named for raptorial claws that resemble a praying mantis's, and they have looked remarkably similar for 100 million years. Australia is a stronghold: the Queensland Museum counts about 150 species from 70 genera in Australian waters, out of more than 450 worldwide. Fishers call them "prawn-killers" because they turn up so often in prawn trawls. Divers know them for the punch and the eyes. Both are real, but the popular stories often outrun the science.

## Smashers and spearers

Mantis shrimps come in two working designs. Smashers, including the peacock mantis shrimp, keep the last segment of the claw folded and strike with its swollen base like a hammer, cracking crabs, snails and other hard-shelled prey. Spearers have that segment armed with long, forward-pointing spines that impale soft-bodied, mobile prey such as worms, shrimps and fish.

They hunt differently too. Smashers forage away from their burrows, while spearers wait in sandy burrows and ambush whatever passes. Mantis shrimps are typically around 10 cm long.

## The punch: what the research measured

The famous numbers come from the peacock mantis shrimp. High-speed filming by Sheila Patek and colleagues, published in Nature in 2004, recorded its club at peak speeds of up to 23 m/s, more than 80 km/h underwater, with accelerations of 6,300-8,000 times gravity.

That speed makes the water cavitate. Vapour bubbles form between the club and the shell, and when they collapse they cause a tiny implosion that produces heat, light and sound. The prey is effectively hit twice: once by the club, then again by the collapsing bubble. Patek's lab measured peak forces of about 1,500 N, more than 2,500 times the animal's body weight, with the whole sequence of blows over in less than 800 microseconds. The Western Australian Museum even notes reports of them cracking aquarium glass.

So is it the fastest strike in the animal kingdom? Not quite. The original 2004 announcement was carefully worded, saying the mantis shrimp "may have" the swiftest kick. The same work compared it with other fast strikers such as the trap-jaw ant, and the fastest known animal appendage now belongs to the Dracula ant, whose snapping jaws reach about 90 m/s.

## The eyes: extraordinary, but not super colour vision

The Queensland Museum describes mantis shrimp eyes as the most complex in the animal kingdom. They hold up to 16 different photoreceptor types (we have three), detect ultraviolet and polarised light, and each eye can judge depth on its own by viewing an object with different parts of the same eye.

Here is where the myth creeps in. Some species have 12 photoreceptor types devoted to colour, spanning deep ultraviolet to far red, and it is often claimed they must see colours far beyond our imagination. When University of Queensland researchers tested this in 2014 with the species Haptosquilla trispinosa, the mantis shrimps could only tell colours apart if their wavelengths differed by 15-25 nanometres. Humans in the same kind of test manage about 5 nanometres. Mantis shrimps turned out to be worse at telling colours apart than humans, honeybees and butterflies.

Instead, the team proposed a different system: the shrimp scan their eyes across a scene and recognise colours directly, without comparing receptor signals the way our brains do, more like a satellite sensor reading a look-up table than a human eye. Colour vision, it turns out, depends on processing as much as on receptors.

## Peacock mantis shrimp in Australia

The peacock mantis shrimp (Odontodactylus scyllarus), also called the harlequin or painted mantis shrimp, is a tropical Indo-Pacific species that grows to about 18 cm and lives from the shallows to about 100 m, according to Reef Life Survey. The Queensland Museum names it among the common mantis shrimps in its guide to Queensland animals and describes it as an active hunter of crustaceans, small fish and molluscs.

Reef Life Survey divers have photographed peacock mantis shrimps at Stradbroke Island in southern Queensland, and in the Indian Ocean the WA Museum lists records from [Christmas Island](https://scubadownunder.com/dive-sites/christmas-island), Cartier Island and Ashmore Reef. Even where they live, sightings take patience. Reef Life Survey records the species at just 2.3 percent of the sites it surveys within its range and notes it is more often shy than curious.

## Mantis shrimps in temperate waters

Southern divers have mantis shrimps too. The Australian Museum notes that more than half of the Indo-West Pacific's species occur around Australia, and that new species are regularly being discovered, even off the coast of New South Wales. Many temperate species live in burrows in sand and seagrass and seldom show more than their eyes, so a patient look into small holes on a muck or seagrass dive is the best way to find one.

## Are mantis shrimps dangerous?

Not to a diver who keeps their hands to themselves, but both smashers and spearers can hurt. The Queensland Museum explains the nickname "thumb splitters": anyone handling these crustaceans can receive a painful wound to the fingers or thumbs. The WA Museum adds that many unwary divers have felt that pain.

The hands-off rule that keeps divers safe around [blue-ringed octopuses](https://scubadownunder.com/blog/blue-ring-octopus-the-oceans-tiny-assassin) and [stonefish](https://scubadownunder.com/blog/stonefish-the-oceans-master-of-disguise) applies here too.

## How to find and photograph mantis shrimps

- **Search the doorways.** Look for holes in sand, gaps between rocks and crevices in coral clumps, then watch for a pair of eyes peering out. - **Approach low and slow.** Move in gradually and do not crowd the burrow; a patient diver will often be watched rather than fled from. - **Never poke one out.** Prodding a mantis shrimp from its hole, especially a female carrying eggs, is unnecessary and risky for both of you. - **Focus on the eyes.** More magnification or a shallower depth of field brings out eye detail found in few other ocean subjects. Because the eyes swivel independently, wait for the moment both face the lens.

Elsewhere in the world mantis shrimps support large fisheries and are susceptible to overfishing and habitat loss, the Australian Museum notes. On Australian reefs they remain one of the great rewards of slow, observant diving.

## Sources

- [Queensland Museum: Mantis shrimps](https://www.museum.qld.gov.au/learn-and-discover/animals-of-queensland/crustaceans/mantis-shrimps) - [Australian Museum: Mantis Shrimp](https://australian.museum/learn/animals/crustaceans/mantis-shrimp/) - [Reef Life Survey: Odontodactylus scyllarus](https://reeflifesurvey.com/species/odontodactylus-scyllarus/) - [Patek Lab, Duke University: Mechanics of movement, mantis shrimp](https://pateklab.biology.duke.edu/research/mechanics-of-ultrafast-movement/mechanics-of-movement-mantis-shrimp/) - [UC Berkeley News: Mantis shrimp may have swiftest kick in the animal kingdom](https://newsarchive.berkeley.edu/news/media/releases/2004/04/21_shrimp.shtml) - [National Geographic: The mantis shrimp sees like a satellite](https://www.nationalgeographic.com/science/article/the-mantis-shrimp-sees-like-a-satellite) - [Larabee et al. 2018: Snap-jaw morphology in the Dracula ant](https://pmc.ncbi.nlm.nih.gov/articles/PMC6304126/) - [Western Australian Museum: Creature Feature, Peacock Mantis Shrimp](https://museum.wa.gov.au/creature-feature-peacock-mantis-shrimp)

Header photo: A peacock mantis shrimp (Odontodactylus scyllarus) faces the camera, stalked eyes and folded smashing clubs on show; photographed in eastern Indonesia, not Australia. by prilfish (Silke Baron), via Flickr, [CC BY 2.0, via Wikimedia Commons](https://commons.wikimedia.org/wiki/File:Mantis_shrimp_(Odontodactylus_scyllarus).jpg).