Stomatopods as Pests

How do you tell if there's a mantis shrimp in your tank?

(A) Fishes and invertebrates like shrimps and crabs start to disappear overnight.

The continued loss of fishes and invertebrates may mean that there is a mantis shrimp somewhere in your tank. Note however that other inhabitants of the aquarium may in fact be responsible for this. Sally Lightfoot Crabs, for example, have been known to devour an inhabitant or two, and predatory fishes that have been mistakenly placed along with more timid (or smaller) fishes may also be the actual culprits. By a process of elimination, make sure that these are no other possible candidates.
This external link takes you to an article whose author is doubtful whether many of the fish disappearances are actually caused by mantis shrimps. I agree with many of his arguments, however, you should note that many of the newsgroup posts concerning problems with mantis shrimp have reported BOTH the loss of fish/invertebrates AND the presence of what they take to be mantis shrimps. Therefore, there seems to be strong circumstantial evidence that mantis shrimps can be the cause of massive losses in livestock. In addition, the author seems to conclude (mistakenly) that all smashers are restricted to a diet of hard-bodied animals. This is not true. Both smashers and spearers can take fishes and shrimps. The smasher raptorial appendage can be used to impale or severely wound soft-bodied prey.

(B) Loud clicking noises are heard coming from the tank.

A lot of people seem to be confused about this. Pistol shrimps, which are "generally" viewed as non-harmful to most inhabitants of the tank, can and do make these clicking noises using one of their enlarged, specialized claws. Mantis shrimps cannot by themselves produce such noises. However, they can and do produce clicking noises whenever they use their raptorial appendages to hammer something hard, whether it be the armored shell of some luckless crab or mollusk, or the walls of their cavities. I have read somewheres that one way to tell from the clicking noises is that pistol shrimps tend to snap in ones and twos, whereas mantis shrimps make rapid multiple hits.
The point here is that clicking noises don't prove anything. However, in conjunction with the continued loss of inhabitants, and the lack of any other viable culprit, you can probably assume that you do have a mantis problem.

What's the difference between mantis shrimps and pistol shrimps?

(taken from an email I sent to a reader)

NOTE: For pics of the two types go to this Marine Aquarist Society of Australia page.

At the very basic level, the two are very different critters, with pistol shrimps belonging to a completely different group of organisms which include lobsters and crabs, while mantis shrimps make up the only living order in a superorder called the hoplocarida. You can tell both apart very quickly by the ff:
Pistol shrimps have two relatively large claws (one significantly larger than the other) that it holds extended in front of it, while mantis shrimps hold their enlarged forelimbs very close to their bodies.
The carapace of a pistols is relatively "long" (ie. covers the head and thoracic segments), whereas in mantises the carapace is extremely short, which makes them look more "wormlike" because of the exposed abdomen and some thoracic segments. This makes the mantises very flexible, and they like rolling around a lot inside their burrows or cavities.
Pistols seem to have a very normal looking shrimplike "rostrum" (I don't own a pistol, so I'm basing this on pics), which is a sharplike extension jutting outwards from their head, while mantis shrimps do not clearly show this structure.
The eyes of pistols are recessed, whereas mantises have extraordinarily stalked and eminently moveable eyes.
Mantis shrimps have a pair of "winglike" antennal scales along the sides of their head, which you can very clearly see if you look at them face to face.
Pistol shrimps make those clicking noises by using one of their specially modified claws. Based from different sources, these are either used in mating, hunting (by stunning small prey), and in fighting with other pistol shrimps. Mantises cannot make clicking noises per se.... instead, any clicking noises from a mantis shrimp are due to using its forelimbs to hit something else, either inanimate objects or (more likely) hardshelled prey such as snails or hermit crabs.
Whether or not pistols are deadly to other inhabitants of the aquarium seems to be an open debate. Some have said they do eat others, while I've read in some reference books that they feed on already dead stuff. I suppose it's really a combination of both, with the shrimp feeding on much smaller prey when the opportunity arises. The mantis is deadly to others (especially when it's pretty hungry), although one mantis that I have has (so far) left other inhabitants alone when kept amply fed. I've seen pics of gobies and pistols cooperating, while I'm sure the mantis would rather eat the fish than live with it. Since your question was sort of general, I gave you a broadsided answer. If you had a specific question, please feel free to email me.

banyanwanderer.