Marvellous mantis shrimps

Mantis shrimps are remarkable invertebrates. They are not shrimps, but an ancient group of crustaceans called stomatopods and they get their name from their large praying mantis-like raptorial claws which they use to capture prey.

Anchisquilloides mcneilli Photo: ©Rob Stewart, NIWA

There are about 450 species of mantis shrimp, and they are found in a wide variety of habitats from the shore down to 1500 m. Most species occur in tropical and sub-tropical waters, although a few species live in temperate and even subAntarctic waters. They play an important role in marine ecosystems, controlling the number of some species and burrowing species increase turnover and oxygenation of sediments. Overseas, several species are fished commercially but they are susceptible to overfishing and habitat loss (Ahyong https://australian.museum/ learn/animals/crustaceans/mantisshrimp/). Mantis shrimps generally grow to about 10 cm long and live for two to seven years. However, there are notable exceptions: some species rarely reach 3 cm while the zebra mantis shrimp can grow to about 40 cm, and the peacock mantis shrimp may live for 20 years. Mantis shrimps are usually solitary and live in burrows, so they are seldom seen but are often attractively coloured, and they have several truly incredible adaptations, including exceptional vision and amazing strike speeds. Their eyes can move independently and may be the most complex eyes in the animal kingdom. Human eyes have three types of light detecting cells while mantis shrimps have 12–16 and they can see polarized light.

Close up of peacock mantis shrimp Odontodactylus scyllarus eyes Photo: Cédric Peneau

There are two main types of mantis shrimp, named after the shape and function of their raptorial claws: ‘spearers’ and ‘smashers’. Most mantis shrimps species are spearers, and they have two sharp claws lined with sharp teeth which they use to stab and snag their prey. They are ambush predators that live in burrows in soft sediments (sand or mud). Spearers mainly feed on evasive prey such as soft-bodied fish and crustaceans, and they can launch their claws at up to 5.7 metres per second.

Smashers are the heavy hitters of the mantis shrimp world. They have two club-shaped limbs, each with a sharp inner edge, which they use to hit, smash apart, and cut their prey. Smashers are foragers and they generally live in cavities or burrows and mainly feed on hardbodied, often slow-moving animals such as crabs and snails which they smash open. Smashers can strike out with their clubs at incredible speed and force. They have one of the fastest strikes on earth (10–23 metres per second) and at an impact force of up to 1,500 Newtons (more than 2500 times their body weight). If one super hit wasn’t impressive enough, they deliver a second shockwave. Their strike is so fast that it creates an area of low pressure, and cavitation bubbles form, which then collapse releasing energy, forming a shockwave. Both limbs are generally used so the unfortunate prey receives four strikes.

New Zealand has 20 species of mantis shrimp, eight are found only in New Zealand and one is invasive. The Japanese mantis shrimp Oratosquilla oratoria was discovered in Kaipara Harbour in 2009 and is thought to have entered New Zealand as larvae in ballast water (Ahyong 2010). It is under sustained control and under

Mantis shrimp Squilla mantis showing spearing raptorial claws Photo: public domain Peacock mantis shrimp Odontodactylus scyllarus showing club like raptorial claws Photo: Prilfish

the Biosecurity Act (1993) it is illegal to keep it in captivity. If you catch one you must destroy it immediately (https://www.nrc.govt.nz/environment/ weed-and-pest-control/pest-controlhub/?pwsystem=true&pwid=20). IN THE AQUARIUM

If you are after a challenge, a mantis shrimp is a great subject for a dedicated local marine aquarium. However, they are voracious predators and will often kill and eat tank mates, including other mantis shrimps, so it pays not to keep them with valuable, or delicate, animals. Also be very careful if you are handling them – spearers are also called thumb splitters, and smashers can deliver a series of very powerful blows and cuts. Most New Zealand mantis shrimps are spearers. They live in burrows in soft sediment, so they need a deep sand bed (as deep as the mantis is long) and a burrow. You can make burrows by burying a U-shaped piece of PVC pipe (with a diameter that is 1.5 X the width of the mantis shrimp) in the sand so that both holes are at the surface.

the invasive mantis shrimp Oratosquilla oratoria Photo: photographer unknown

Hemisquilla australiensis in captivity Photo: Mark Paterson

Although most species are solitary, if you have a very large tank and the burrows are well spaced, you may be able to keep more than one spearer in the same aquarium. A chilller will likely be required in warmer areas particularly over summer. Spearers can be fed on live, or frozen, fish or prawns. Put frozen food on a skewer and wave it about in front of their burrow or even touch them gently with it. They may take a while getting used to frozen food (which should be soaked in nutrient and calcium supplements) but keep trying and they will hopefully start eating it. Mantis shrimps should be fed once a day to two times a week.

Odontodactylus hawaiiensis Photo: NIWA

Bathysquilla microps Photo: ©Chris Thomas, NIWA

Mantis shrimps are not allowed to be imported into New Zealand. Overseas, the strikingly coloured peacock mantis (Odontodactylus scyllarus), a rock burrower (smasher), is often kept in captivity. Tropical smashers, including the peacock mantis shrimp, are very rare but occasionally captured in northern New Zealand. Compared to spearers, smashers are a little easier to keep in captivity. You will need a tank with a sand substrate and some live rock, preferably with holes/ crevices in it for the mantis shrimp to live in (they will smash a hole in the rock if a suitable one isn’t available). Smaller smashers may live in large shells. Smashers can be fed on small hermit crabs and crabs. They may eat fish but they need at least some hard-shelled prey in their diet. Some smashers can damage live rock and there are occasional reports of them breaking aquarium glass. This is unlikely unless they are taunted although they may break glass during digging. Large smashers (>15 cm) should probably be kept in acrylic aquaria or at least in an aquarium with an acrylic base. Smashers may also hitchhike in live rock. If you own a tropical marine tank, be careful when purchasing live rock. It can sometimes contain a juvenile mantis shrimp which may become an unwelcome pest.

Peakcock mantis shrimp Odontodactylus scyllarus Photo: Charlene McBride

Thanks to Kareen Schnabel, NIWA, for her feedback on an earlier version of this article. Darren Stevens & Mark Paterson

References

Ahyong, ST (2010). Japanese shrimp makes NZ debut in Kaipara Harbour. Seafood New Zealand 18: 11–12. Ahyong, ST (2012). The Marine Fauna of New Zealand: Mantis Shrimps (Crustacea: Stomatopoda). NIWA Biodiversity Memoir 125. Ahyong, ST. Mantis shrimp. https://australian.museum/learn/animals/ crustaceans/mantis-shrimp/. Retrieved July 2022 Caldwell, R. Roy’s list of stomatopods for the aquarium; the identification and care of mantis shrimp. https://ucmp.berkeley.edu/ arthropoda/crustacea/malacostraca/eumalacostraca/royslist/index. html#directory. Retrieved July 2022 deVries, MS, Murphy, EAK, Patek SN (2012). Strike mechanics of an ambush predator: the spearing mantis shrimp. Journal of Experimental Biology 215: 4374–4384. https://doi.org/10.1242/jeb.075317 Hansford, D (2020). Aliens on earth. NZ Geographic 164: https://www. nzgeo.com/stories/aliens-on-earth/. Retrieved July 2022 Heim, M. (2021). A peacock of a different feather. https:// thefisheriesblog.com/2021/11/15/peacockmantis/#:~:text=It%20is%20 also%20one%20of,one%20of%20the%20strongest%20species. O’Shea, S, Raethke, N, Clark, M (2000). Bathysquilla microps – a spectacular new deepsea crustacean from New Zealand.Seafood New Zealand 8(9): 36. Patek, SN, Caldwell, RL (2005). Extreme impact and cavitation forces of a biological hammer: strike forces of the peacock mantis shrimp Odontodactylus scyllarus. Journal of Experimental Biology 208: 3655–3664. https://doi.org/10.1242/jeb.01831 Patel, P (2019). Camera Mimics Mantis Shrimp’s Astounding Vision. Scientific American 320: 12. https://www.scientificamerican.com/ article/camera-mimics-mantis-shrimps-astounding-vision/ Wuest, P (2019). What Happens When a Mantis Shrimp Packs a Punch? The research behind one of the most fascinating mechanisms in the animal kingdom. https://www.sportdiver.com/what-happens-whenmantis-shrimp-packs-punch. Retrieved July 2022 Mantis shrimp (Lysiosquillina maculata). http://www.theaquariumwiki. com/wiki/Lysiosquillina_maculata. Japanese mantis shrimp. Squillidae –Oratosquilla oratoria. Northland Regional Council. Te Kaunihera ? rohe o Te Taitokerau. https:// www.nrc.govt.nz/environment/weed-nd pest-control/pest-controlhub/?pwsystem=true&pwid=20

Peakcock mantis shrimp Odontodactylus scyllarus Photo: François Libert