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People are constantly posting on forums wondering whether or not they have a Mantis Shrimp or a Pistol Shrimp in their system. This is usually a result of hearing clicks in the night, here is a short article on how you can differentiate a Pistol Shrimp from a Mantis Shrimp.

Clicking and ID
Not all Mantis Shrimp (or Stomatopods to give them their real name) emit the clicking sounds often heard from a reef keepers tank, only the smashing type of Mantis do this (although all are capable), and this noise is usually often heard when they are tending their burrow by chipping pieces of rock away or when they are striking their prey, such as crabs, snails or other hard shelled invertebrate with their extendable raptorial appendages, which can be seen on the image to the right. For video footage of this please look at the video section. Spearing types of Mantis such as Pseudoquilla ciliata will not make themselves known as they spear their prey (your valuable fish or ornamental shrimps) and no noise will be heard. The most common type of hitchhiking Stomatopod is Gonodactylellus viridis from Bali, Fiji and other Indonesia, and from Florida rock Neogonodactylus wennerae are almost guaranteed.You will most likely see the bulging eyes of the Mantis protruding from its burrow. Both these mantis remain quite small, N wennerae specifically, and will leave 99% of fish alone, however you will find that your clean up crew are slowly disappearing. Some people say that Mantis shrimps can break glass, this is true, but for only two species that you are not likely to find in your rock. For removal techniques please see the Removing/Catching a Stomatopod article.
Pistol shrimps (also known as Snapping Shrimp) click for a totally different reason and in totally different ways. As you can see from the photos Pistol Shrimps claws are totally different to Mantis Shrimps and are fully extended 100% of the time, and unlike a Stomatopod they do not have the option of tucking them under their bodies. The clicking/snapping of a Pistol shrimp is just as interesting as a Stomatopod's appendages. Pistol Shrimps usually have one claw larger than the other, this is the claw which will be used for creating the cavitation bubble that we hear the click from. The claws are segmented unlike a Mantis Shrimp. After the Pistol Shrimp draws back one half of its claw (like cocking a gun) it snaps it shut causing a cavity bubble that generates acoustic pressures of up to 80 kPa at a distance of 4 cm from the claw. This is the clicking noise we hear from a Pistol Shrimp.
Now you know how these animals create the sounds that they do, you need to find out which you have. An easy way to determine this is 95% of Stomatopods are diurnal, opening their burrows when the lights come on (clicking may be heard here) and then closing their burrows again at night. Any clicking in between could be the animal feeding or tending its burrow. Pistol Shrimps are usually nocturnal animals, becoming more active at night. If you hear the clicking through the night you most probably have a Pistol Shrimp, some people think these are harmless but others believe they can be a terror in a reef aquarium. If not well fed they have the capability to kill small fish (although rare, the fish would have to be very close by or holed up in a rock or similar) and small Shrimps.


Pistol Shrimp - note the extended arms that are unable to be folded back


Mantis Shrimp (rare Gonodactylellus affinis), note the raptorial appendages (arms) that are folded under the body.

To Keep or Not to Keep?
Ok so you now know you have either a Stomatopod or a Pistol Shrimp, what should you do and what harm could they cause?
Mantis Shrimps, depending on the species of course (but presuming they are smashers and not spearers), would be relatively harmless in a tank with large fish and corals. The Mantis shrimp would however be seen as food for larger predatory fish such as Puffer and Triggerfish and would kill and eat any small shrimps (including Cleaner Shrimps, Blood Shrimps etc), crabs such as Mithrax and Sally Lightfoots. Starfish and Urchins would usually be left alone. Stomatopods often build burrows under or in rock and could cause rock fall if your rock is not stable.
Pistol Shrimp threats vary depending on size and species. Most small Pistol Shrimps rarely leave rocks and rarely cause problems in home aquariums. Larger Pistol Shrimps can cause problems for small fish and shrimps too if not kept well fed. If you wish to remove your Mantis or Pistol Shrimp please see the Removal article for instructions on how to remove them.
If you wish to keep your Mantis shrimp i would strongly suggest buying a small nano tank (5 gallons and up) to dedicate to this animal as they make fascinating species tanks and are very intelligent. If you wish to keep your Pistol shrimp it might be worth trying to pair it up with a Goby of some kind. Find out what sort of Pistol Shrimp you have and find out what the best Goby would be. The Pistol Shrimp and Goby (often Watchman or Yashmak Gobies) will form a symbiotic relationship (this is not guaranteed, but most people eventually have success) where the Pistol will dig tunnels for the goby to hide in and the Goby will keep look-out for any possible predators. With the Pistol Shrimp having very poor eyesight it will stay very close to the Goby, usually with one antenna on the gobys body. In return the Goby gets a nice home built for him!

Article & images copyright to MantisShrimps.co.uk, please do not use without prior concent.
Thanks for looking!
James