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Frequently-Asked-Questions (FAQ)

Last Updated: November 10, 2002

Should I keep my mantis in an acrylic tank? (ASJ)

Mantis that are below a certain size (around 9-10 cm) are probably not be capable of breaking your glass tank. Even mantis shrimp that are larger very RARELY will be agitated enough to try breaking the glass. Dr Caldwell notes that he has seen only Odontodactylus, Gonodactylus chiragra, and Hemisquilla do this.

Thus, keeping your mantis in a glass tank will probably not be a problem.


What mantis makes the best pet? (Dr. R. Caldwell)

While I certainly agree that Odontodactylus scyllarus, aka peacock, painted, harleguin mantis) are interesting, interactive and big, they to have problems. Large males are prone to shell disease and both sexes have difficulty molting in captivity and frequently lose a raptorial appendage. I wish we could point to these problems and say that they are simply cases of poor diet and/or water quality, but unfortunately, we can't identify all of the factors involved. As an aside, they do not have the best vision, although they certainly see well enough.

For me personally, I prefer some of the smaller Odontodactylus, O. brevirostris from Hawaii and O. havanensis from Florida. THey are even more interactive than O. scyllarus, are a bit easier to keep (although they don't live as long), and generally do more.

Other favorites would be Gonodactylus smithii, by far one of the most spectacularly color stomatopods, and Pseudosquilla ciliata, the cats of the manitis shrimp family.

It is unfortunate that Odontodactylus other than O. scyllarus aren't available. THey make superb residents of small systems. I keep my research animals in 1 gal tanks with a simple Fluval and two inches of sand/coral gravel and they do very well.

O. havanensis is common off the Florida Keys, but generally lives at 20 m + on open sand plains.

O. brevirostris is common in Hawaii at 10 m+ on coralline algal slopes.

O. latirostris is common in Indonesia at 10m+ on open plains.

I have been trying for a couple of years to find divers interested in collecting these species, but so far without success. For my research, I go get them myself. Given that I usually can collect and transport back to Berkeley more than 30 animals or so, they usually end up costing my at least $100 each. If I could purchase them at the same price as O. scyllarus, I would be buying all I could find.

The most common to show up is the occasional O. havanensis from Florida since they occur in the same habitat and have the same kind of burrow as yellow jawfish.

- Dr. Roy Caldwell

Are mantis shrimp diurnal or nocturnal? (Dr. R. Caldwell)

Whether a mantis shrimp is diurnal, nocturnal or crepuscular (dawn and dusk) depends on the species. Most of the species of mantis shrimp that people keep are diurnal. That includes almost all gonodactylids and pseuodsquillids. Even here, there are definite peaks of activity during the day. A typical gonodactylid (Gonodactylus chiragra, G. platysoma, G. mutatus, Neogonodactylus wennerae, etc.) opens its cavity at dawn, forages actively for a few hours and is more likely to stay in the cavity around 10-2. Then there is another peak of foraging and the animals begin closing up their cavity just before sunset. In the field, tidal cycles and alter this pattern.

Odontodactylus scyllarus is a bit of a puzzle. They are primarily active during the day, but also come out at night, particulalry when there is a full moon. They usually do not seal their burrows on a daily cycle.

A few people are starting to keep Lysiosquillina. They hunt day and night, but usually don't leave their burrows.

Echinosquilla from Hawaii and the central Pacific is one gonodactyloid that is crepuscular. You don't see them in their burrow entrances until dusk, then they move to the entrance and you start to see eyeshine from a dive light.

If you don't have an Ondontodactylus scyllarus and you hear clicking in your live rock at night, you can be pretty sure that it is not a stomatopod. The most likely culprit is a snapping shrimp.

- Dr. Roy Caldwell

How difficult is it to raise adult stomatopods from larvae? (Dr. R. Caldwell)

Stomatopod larvae have only been reared successfully from the egg a few times. Brine shrimp nauplii don't seem to provide adequate nutrition. I have had limited success treating them with an additive such as Selco. Your greatest problem, however, is likely to come fromt the fact that the larvae are very cannibalistic. Most people who have had success rearing them have kept only one per container. That makes for a lot of work.

Assuming that you have a gonodactylid such as Neogonodactylus wennerae, the larvae remain with the female for about a week undergoing three molts. They do not feed during this time. After the fourth molt, they become attracted to light, swim out of the cavity and start feeding. Generally in a standard aquarium, they will starve to death in two or three days. If you can get them to feed, they will molt four more times and finally settle as postlarvae in a month. If you have O. sycllarus larvae, we don't know how long they stay in the plankton since they have never been reared. However, given the size at which they settle, it is probably atleast three months or more.

- Dr. Roy Caldwell

How difficult is it to buy a spearer vs a smasher? (Dr. R. Caldwell)

There are a couple of misconceptions (about spearers). The first is that spearers are frequent stowaways in Live Rock. Almost all spearers live in burrows in sand or mud. They do not frequent live rock and even if a Pseudosquilla or Raoulserenea were in a rock (the two most likely general to be found in hard substrate), they are less resistant to desication and would almost certainly bail before the rock was shipped. Neogonodactylids from the Caribbean are fairly common in LR and are small and tough as nails frequently surviving even in "well cured" rock.

The second issue is whether it is even possible to order a spearer. Aside from Lysiosquillina maculata which is easily identified as the "large striped brown and yellow mantis shrimp that is eaten", you would be hard pressed to explain to most importers and collectors what you want when you say "spearer". This is a term that I used 27 years ago and while it means something stomatopod lovers, it doesn't mean a thing to most local collectors. Asking for a "yellow" mantis shrimp might get you a P. ciliata since on some reefs the yellow morph does occur, is easy to spot, and there are very few other stomatopods that are solid yellow. However, for every yellow morph, there will be dozens of green, brown, black and sandy colored P. ciliata. They are rare. I recently collected for a month on some of the most pristine reefs in northern Australia and saw only two yellow Pseudosquilla ciliata.

Collectors will only collect what is economically feasible. Most spearers are very difficult to collect alive. It isn't easy getting them out of their burrows in one piece and running them a species like P. ciliata down on a reef flat takes time. On a good day in Hawaii where P.c. populations are some of the highest I've seen, a good day's collection would yield half a dozen. In the same time, I could collect 50 Gonodactylus mutatus and even more valuable fish. If I'm a collector, I might grab a spearer (if I knew what it was and if I knew it was wanted) when I saw one, but I would not be out their specifically targeting them. About the only species of mantis shrimp for which that occurs is O. scyllarus. The collectors know there is a market, you can easily find and collect several on a dive, they are hardy, and the local exporters will pay for them.

- Dr. Roy Caldwell

How often do mantis shrimp molt? (Dr. R. Caldwell)

It all depends on species, size, and reproductive condition. Small juveniles can molt every two weeks, larvae even faster. However, if you are talking about an adult gonodactyloid (gonodactylid or Odontodactylid, every three or four months is average. However, it can be longer. I have an adult O. havanensis that just molted today for the first time since I captured it last July.

- Dr. Roy Caldwell

Why do some mantis shrimps' raptorial appendages "fall off"? (Dr. R. Caldwell)

First, stomatopods have ways of dealing with this. If they are missing a single raptorial appendage (2cd maxilliped), there is no modification of the molt cycle and they molt at a normal rate. They usually have no problem feeding, although smashing shells may take a bit longer. If the entire appendage is lost, after one molt there will be a small, poorly colored appendage. It will not be functional. After a second molt, it will be a little more than half size and will move, but not strike very well. After a third molt, it will be 3/4 size and functional (but weaker). After a fourth molt, you won't know the difference. Given that it may be a couple of months or more between molts, it can take up to a year to regenerate the appendage. Juveniles can do it in a couple of months.

If both appendages are lost, the animal has to eat prey that it can chew - worms, soft meat, etc. However, it will put all of the energy it can into molting resorbing the ovaries or testes, etc. It will molt up to 50% faster and if it is fed well, can grow the appendages back to full size in about 2/3 the time it takes to grow back one. Obviously, however, this is at a cost. It does not reproduce and energy reserves are dangerously low.

As to why the animal lost both rapts, I would guess some sort of stress. Heat, cold, salinity, organic solvents, etc. can all cause the muscles in the raptorial appendages to be permanently damaged. The rapts don't fall off, the stomatopod literally breaks them off. Stomatopods can't autotomize its claw the way a lobster or crab does, so it grabs the appendage with the other maxillipeds and twists it back and forth until it breaks free.

The other common cause of rapt loss is during the molt, but often this involves just a single rapt. Also, loss during molting is not as common in Gonodactylids as it is in O. sycllarus.

- Dr. Roy Caldwell

I have a female Odontodactylus and im thinking about adding a male to the 20gal tank. is this a good idea? will they fight? (Dr. R. Caldwell)

Eventually. They probably will mate when you put them together and they may even cohabitat in the same burrow, but sooner or later they will not be able to get far enough away from one another and a fight will break out. Alternatively, one will molt and the other will cannibalize her/him. Also, if the female lays eggs, she will probably attack the male.

There are a number of monogamous lysiosquillids that will live together happily in one burrow for years, but I know of no gonodactyloid (Gonodactylus, Odontodactylus, Pseudosquilla, Haptosquilla) that will live together for mor than a few days.

I have been able to keep a couple of Odontodactylus havanensis together in a 125 gal tank with lots of room to build burrows and even this doesn't always work.

- Dr. Roy Caldwell

How dangerous are the strikes of common mantis shrimps to humans? (Dr. R. Caldwell)

I handle stomatopods every day in our lab and when I'm in the field it is not uncommon to measure and sex 150 animals in an evening. Needless to say, I'm struck fairly often. Some species are far worse than others, but it usually hurts. Even a 2 cm Gonodactylus can draw blood and a 4 cm animal can drive the dactyl tips to the bone. Aside from a two inch slice in my hand made by a large lysiosquillid (by the uropod spine, not the dactyl), the most severe injury I have incurred was from a 7 cm Gonodactylus chiragra that drove its dactyl into the joint of my index finger and the tip broke off. It took some minor surgery to remove it. But that is nothing compared to what happen to a diver from South Africa who wrote me a few years ago describing his attempt to grab by hand an 18 cm Odontodactylus. The animal severely injured his finger which became infected by a chiton-digesting bacteria. The infection did not respond to the usual antibiotics. In the end, they amputated the finger. Be careful out there!

- Dr. Roy Caldwell

Editor's Note: There are newspaper reports of large Hemisquilla cutting off people's fingers with one strike, although how much credence can be given to stories like these is open to doubt.

What is the average life expectancy of most mantis in captivity? (Dr. R. Caldwell)

"We have kept them (Odontodactylus scyllarus) in the lab for three or four years and in the field I suspect they live at least five or six years. Other species live much longer. We have one adult Lysiosquillina that is about 25 cm long. It has not grown since we got it (although it molts every three months) and it has been in the lab for 5 years."

- Dr. Roy Caldwell

Are stomatopods shrimps? (ASJ)

No. Although stomatopods belong to the same class (Class Malacostraca) as crabs and shrimps, they form their own SuperOrder (Hoplocarida), which contains the single order Stomatopoda.

How big can they get?

Stomatopods range in size from 1-2 cm to more than 30 cm in the case of some deeper-water lysiosquillids. Smasher types tend be smaller than spearers.

Can mantis shrimps really break aquarium glass? (ASJ)

Yes. The larger smashers (>9 cm) certainly can. A 9 cm smasher once made headlines in the U.K. by smashing through its tank. I had another 9 cm specimen break the hard plastic container that it was in with a single, very loud strike.

A large 25 cm Californian species (Hemisquilla ensigera) can strike with a force approaching that of a small-caliber bullet, and can easily break a double layer of safety glass.

Are mantis shrimps intelligent? (ASJ)

It depends on where the cutoff point for intelligence is set. Although it is unlikely that a stomatopod will ever get a perfect score in any collegiate entrance examination, researchers have discovered that these crustaceans do pack some intellectual brainpower.

Dr. Roy Caldwell notes:

(Stomatopods have the) ability to distinguish colors, polarization patterns, and shape. (My very first study was to train a stomatopod to distinguish between a right side up and up side down equilateral triangle.) We have also observed them learn to open unfamiliar shell morphologies and change the size of prey taken depending on the risk of foraging. Then there are the learning to recognize other individuals studies. Within the constraints of being able to manipulate objects, they appear to be able to do everything that large octopus can and then some. Memory wise, the longest ability to discriminate between two individuals I have documented is a month.

The unique rotating eyes of stomatopods tend to make people ascibe some intelligence in their behavior. If you have ever kept a mantis shrimp, you will notice that they spend lots of time just peering out of their lairs, following your movements as you bustle about on the outside. In addition to being really "cute", such behavior prods one into believing (whether rightly or wrongly) that some consciousness is at work behind those crazily rotating eyeballs.

To find out more about stomatopod learning, click here.

How fast can a mantis shrimp strike? (ASJ)

Stomatopod strikes are one of the fastest known movements in the animal kingdom. Although they exist in a medium significantly denser than air, their strikes are 10 times faster than those of the land-based Praying Mantis. The raptorial appendages of stomatopod spearers can go from full rest to a speed of 10 meters/second in 4-8 milliseconds.

Other very fast movements in the animal kingdom include the strike of an Odontomachus ant (the mandible tips of these large ponerine ants travel at 8.5 m/sec and closes within 1 millisecond); the jump of a springtail at 4 milliseconds; and the escape response of a cockroach at 40 milliseconds.

How can I tell that a mantis shrimp is in my reef tank? (ASJ)

There are several ways to tell if you have a mantis shrimp in your setup, and they are listed in the Stomatopods as Pest section.

How can I get rid of a mantis shrimp in my reef tank? (ASJ)

A sample of the numerous and inventive ways to get rid of mantis shrimps are listed here.

What do mantis shrimps eat? (ASJ)

Spearers tend to specialize in softer-bodied prey, including shrimps, fishes, and cephalopods such as squid and octopus. The smashers favor hard-bodied prey such as crabs, lobsters, clams, and snails. However, smashers will also take fish and other similar prey when necessary; their raptorial appendages end in a wickedly sharp point which will easily pierce soft flesh.

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