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Mantis Shrimp Kate Redman

Within the realm of invertebrates, the general public may consider the Cephalopods (e.g., octopus and squid) as harbouring the only truly intelligent species. However, many scientists regard other marine invertebrates as having decent levels of cognitive abilities, especially crustaceans in the order Decapoda. Take, for instance, mantis shrimps.

Mantis shrimps belong to the order Stomatopoda, within the class Malacostraca. Malacostraca is the largest of the six classes of crustaceans [1], and contains crabs, lobsters, crayfish, shrimp, krill, and woodlice. There are approximately 500 different species of mantis shrimps recognised from around the world [2], with the majority growing to approximately 10 centimetres in length [3], although individuals of 38cm [4] and 46cm [5] have been discovered. Diet, and mode of prey capture, further separates stomatopods into two distinct groups: the smashers, and the spearers. The ‘smashers’ have club-like claws, which they use to crack open the shells of crabs, snails, and other molluscs;  meanwhile, the ‘spearers’ use sharp, barbed claws to ensnare soft-bodied fish. Most mantis shrimp species live in tropical and subtropical seas, in the Indian and Pacific Oceans between eastern Africa and Hawaii, with a few living in temperate seas [3].

Mantis shrimp, with a few exceptions, are solitary sea creatures. The exceptions to the rule being spearers of the Lysiosquillina genus [6], some of which form monogamous pairings. Stomatopods live in burrows, which can either be a part of a natural rock formation, or created by the shrimp itself burrowing a passageway into the sea bed. Home type tends to depend on the species of shrimp, with spearers living in excavated burrows, and smashers occupying cavities in coral rubble, or other hard substrate [7]. Stomatopods spend most of their time hiding out in their home burrows, often only exiting to hunt or find a mate. Modes of reproduction are equally varied, and range from extreme promiscuity within the smashers [8], to the monogamous spearers mentioned above. In one species, Pseudosquilla ciliata, the female initiates courtship through visual displays and a vigorous sexual chase [9]. Depending on the species, the eggs will then either be homed within the safety of a burrow, or carried around under the female's tail until they hatch [3]. In terms of longevity, some species can live for 20 years [3].

Mantis shrimps are dexterous, have exceptional senses, posses good memories, and are adept at learning. For starters, they can recognise other individuals through a combination of visual and chemical cues, and will adapt their behaviour in response to the previous encounter they had with that specific opponent [10]. Experiments have shown that when a mantis shrimp, for example Gonodactylus festai, fights and loses against a dominant individual defending its home cavity, it will subsequently avoid cavities containing water, and hence the scent, from the victor, even if the dominant mantis is no longer in the cavity [11]. In a non-combatant scenario, Haptosquilla glyptocercus (a species that is very variable in colouration) was able to recognise other individuals visually, displaying more interest in strangers than individuals they had previously seen [12]. Further, although the types of mating behaviours of stomatopods are varied, the different species take part in ritual courtship. However, the flexibility seen in their behaviour, and in the decisions that get made (such as avoiding aggressive contests with previous mates [10]) suggests that learning is likely involved [12].

Moreover, when it comes to food, these animals can learn to identify and effectively manipulate prey items. Their nimble maxillipeds (food-handling appendages) allow stomatopods to interact with their environment with great precision, giving them the ability to select and manipulate objects for burrow construction, prey handling, mating, and other behaviours [12]. Also, stomatopod eyesight puts ours to shame. Their eyes carry 16 types of colour receptive cones, as opposed to our three, and it is likely they can perceive colours outside the human visual spectrum [3]. They can also see polarized light. Their advanced vision, coupled with their complex brains and manual dexterity, means stomatopods can learn to distinguish the colour of a container containing food [13], as well as its shape [14]. Moreover, when presented with a container of food where only one side is accessible (e.g., a smasher is presented with a box with only one breakable side) they can learn which side to crack to retrieve the meal [14], quickly turning the object to get at it. Additionally, when presented with a new prey type, they will perfect their hunting strategy, and become more adept at accessing the reward over time (e.g., reducing the number of blows it takes to crack open a snail shell [16]).

At present, only a small percentage of the 500 species of stomatopods are used in aquaria [2], such as the peacock mantis, Odontodactylus scyllarus, due to its bright colouring, but their popularity is growing. When keeping stomatopods in an aquarium, whether for a personal display, or for research, it is important for future caretakers to be aware of the cognitive abilities displayed by these shrimps, and provide suitable habitats that minimise stress. Because of their intelligent nature, mental enrichment will be an important thing to consider. With smashers, this can be provided by the introduction of novel food items that they have to learn to access, in spearers, providing live huntable prey, such as small shrimp, should keep them mentally active.

Creating a suitable habitat within the aquarium will also be crucial to keeping mantis shrimp’s healthy. Due to their aggressive behaviour, it is best to home any mantis on its own, and away from any other prized aquarium species, which will probably be seen as food. Depending on the species of shrimp, rock formations with holes in, suitable sediment (and depth of sediment) to dig in to, or imitation homes made from piping, or other suitable material, will need to be provided. For instance, the peacock mantis, a smasher that can reach 20cm in length, will require a 100 litre tank (at least), with sides that can withstand heavy impacts, filled with a deep substrate and live rocks [17 & 18]. Spearers are less likely to damage a tank, but even so, they too will need a good amount of space and suitable substrate. The zebra mantis (aka striped mantis, Lysiosquilla maculata) gets bigger than a peacock (about 40cm) and would do well to be homed in a tank of approximately 120 litres, filled with a deep fine/mixed grade substrate [17]. In addition, for both smashers and spearers, efficient filtration will be required to deal with their messy, high meat diet.

Water quality will also need to be taken into account, though information on this tends to be limited, most likely due to mantis shrimps not being a commonly kept species. Advice ranges from no particular needs, so long as it’s a saltwater tank with the water well filtrated [18], to stomatopods requiring water temperatures of 23-27oC, and salinities of 1.020-1.022sg (26.6-29 ppt) [19]. Seawater pH is between 7.5 to 8.4 [20]. As stated earlier, stomatopods exist in oceans ranging from temperate to tropical, therefore, if you intend to keep one, it is best to thoroughly research your chosen species and its habitat before setting up a tank. When it comes to lighting, low levels are best [18] and, again depending on the species, should be set on a timer to mimic their natural cycle [19].

Generally, stomatopods are a robust species, often finding themselves in an unsuitable tank environment, unknowingly brought there in a live rock, yet surviving with no problems. However, disease can still be an issue. "Shell rot", also known as "shell disease", seems to be the most common health problem for mantis shrimps, and can be fatal. The disease manifests as blotches on the exoskeleton of the shrimp. The bacteria then proceed to eat away at the carapace, down into the animal’s flesh. The direct cause of the affliction, or the pathogen responsible, is unknown [21], hence there is currently no sure-fire preventative or cure. However, stress seems to be a possible factor [22], which makes it even more important that an appropriate environment is provided for your animal. Parasitic load can also be an issue, especially if the animal was sourced from the wild. Several smasher species within the family Gonodactylidae are known to harbour small, parasitic sea snails (Caledoniella montrouzieri) which may inhibit a shrimp’s growth, and moulting and egg-laying abilities [23].

Whether considering a mantis shrimp for a home or public aquarium, it is important to be aware of the problems associated with keeping and showing these animals. Stomatopods are active hunters and home makers, and as such, can cause havoc in a display. They can eat the other inhabitants of a tank, with spearers hunting fish and cephalopods, and smashers destroying sea snails and fellow crustaceans, and some rock-burrowing species can damage the live rock within a set-up. They can also be dangerous towards their caretakers, and because of their weaponised appendages, they should never be fed by hand. Even tongs and tweezers can be lost to a fearless mantis [18]. It is also worth noting that, because they spend most of their lives in tunnels, they can be rather dull subjects for an exhibit unless creative ways of displaying them are employed (e.g., transparent PVC tubing ‘caves’). Not only that, but the formidable clubs of smashers, when wielded by some larger species, can break aquarium glass [24].

As we learn more about the animals in our world, the more we learn that intelligence is not reserved for the 'higher' terrestrial mammals. It is our responsibility as aquarists to ensure the animals in our care have the best habitat possible, and in so doing, we can ensure our animals live a long and stress-free life.

[1] Malacostraca (https://en.wikipedia.org/wiki/Malacostraca) Accessed 05-March-2016

[2] Roy's List of Stomatopods for the Aquarium (http://www.ucmp.berkeley.edu/arthropoda/crustacea/malacostraca/eumalacostraca/royslist/) Accessed 04-March-2016

[3] Mantis shrimp (https://en.wikipedia.org/wiki/Mantis_shrimp) Accessed 04-March-2016

[4] Large shrimp thriving in Ala Wai Canal muck (http://the.honoluluadvertiser.com/article/2003/Feb/14/ln/ln01a.html) Accessed 04-March-2016

[5] Florida fishermen catch "Giant Shrimp" length 46 cm (http://www.chinatimes.com/realtimenews/20140906001704-260408) Accessed 04-March-2016

[6] Secrets of the Stomatopod (http://www.ucmp.berkeley.edu/aquarius/monogamy.html) Accessed 09-March-2016

[7] Caldwell, R.L., & Dingle, H. (1976). Stomatopods, Scientific America, 234, 80-89. Summarised in [10].

[8] Caldwell, R.L. (1991). Variation in reproductive behavior in stomatopod crustacea. In R.

Bauer & J. Martin (Eds.), Crustacean sexual biology, pp 67-90. New York: Columbia University Press. Summarised in [12].

[9] Hatziolos, M. E., & Caldwell, R. L. (1983). Role reversal in courtship in the stomatopod

Pseudosquilla ciliata (Crustacea). Animal Behaviour, 31, 1077-1087. (http://www.sciencedirect.com/science/article/pii/S0003347283800153)

[10] Vetter, K.M., & Caldwell, R.L. (2015). Chapter 2: Individual Recognition in Stomatopods. In L. Aquiloni, E. Tricarico (Eds.) Social Recognition in Invertebrates, pp 17-36, Springer. (http://www.springer.com/cda/content/document/cda_downloaddocument/9783319175980-c2.pdf?SGWID=0-0-45-1509975-p177335312)

[11] Caldwell, R.L. (1979) Cavity occupation and defensive behaviour in the stomatopod Gonodactylus festai: Evidence for chemically mediated individual recognition, Animal Behaviour, 27(1) pp 194-201.


[12] Cronin, T. W., Caldwell R. L., & Marshall J. (2006). Learning in Stomatopod Crustaceans. International Journal of Comparative Psychology, 19, pp 297-317 (https://ib.berkeley.edu/labs/caldwell/Caldwell%20pdfs/IJCP_CroninCaldwellMarshall_2006.pdf)

[13] Marshall, N. J., Jones, J. P., & Cronin, T. W. (1996). Behavioural evidence for color vision in stomatopod crustaceans. Journal of Comparative Physiology A, 179, pp 473-481. (http://link.springer.com/article/10.1007%2FBF00192314)

[14] Chen, K. & Caldwell, R. (2014). Simple Shape Learning of the Two Stomatopod Species: Haptosquilla trispinosa and Pseudosquilla ciliata. Berkeley Scientific Journal, 19(1) pp 56-63. (http://www.springer.com/cda/content/document/cda_downloaddocument/9783319175980-c2.pdf?SGWID=0-0-45-1509975-p177335312)

[15] The Fastest Claw In the West (part 3 of 3) (https://www.youtube.com/watch?v=ua794XPMUlg) Accessed 04-March-2016

[16] Caldwell, R.L., & Childress, M.J. (1990). Prey selection and processing in a stomatopod crustacean. In R.N. Hughes (Ed.), Behavioural mechanisms of food selection, pp 143-164. Springer. Summarised in [12].

[17] Mantis shrimps: Ultimate assassins (http://www.practicalfishkeeping.co.uk/content.php?sid=2978) Accessed 03-04-2016

[18] Mantis shrimps: The prawn supremacy (http://www.practicalfishkeeping.co.uk/content.php?sid=6159) Accessed 03-04-2016

[19] Mantis Shrimp (Order: Stomatopoda) – Part II, Care in Captivity (http://blogs.thatpetplace.com/thatfishblog/2008/07/16/08/#.VwJL6XV97OQ) Accessed 03-04-2016

[20] Seawater (https://en.wikipedia.org/wiki/Seawater) Accessed 03-04-2016

[21] Shell Disease In Stomatopods (http://www.dfwmas.org/shell-disease-in-stomatopods-2684.html) Accessed 03-04-2016

[22] Shell Rot & Peacock Mantis Shrimp (O.scyllarus) (http://thereefuge.com/threads/shell-rot-peacock-mantis-shrimp-o-scyllarus.5532/) Accessed 03-04-2016

[23] Reaka, M.L. (1978). Effects Of An Ectoparasitic Gastropod, Caledoniella montrouzieri, Upon Molting And Reproduction Of A Stomatopod Crustacean, Gonodactylus viridis. In The Veliger, 21(2), pp 251-254. (http://biodiversitylibrary.org/page/42515155)

[24] Shrimp spring into shattering action (http://usatoday30.usatoday.com/tech/columnist/aprilholladay/2006-01-09-shrimp_x.htm) Accessed 13-

By prilfish from Vienna, Austria (Mantis Shrimp macro - Odontodactylus scyllarus) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons