Snapping Shrimp (Pistol Shrimp): Characteristics, Behavior and Loud Noise

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twistclaw pistol shrimp (Alpheus clamator)

Snapping shrimp (also known as pistol shrimp or alpheid shrimp) belong to the family Alpheidae. They are shrimp, characterized by having asymmetrical claws, the larger of which is typically capable of producing a loud snapping sound. The family is diverse and has a worldwide distribution, with around 1,120 species within 38 or more genera. The two main genera are Alpheus, with over 330 species, and Synalpheus, with over 160 species. Most snapping shrimp dig burrows and are commonly seen in coral reefs, seagrass beds and oyster reefs. Most live in tropical and temperate coastal and marine waters. They often live inside sponges and are the only known marine species that live in colonies that resemble the colonies of bees and wasps. The colony often consists of a two parents and a whole bunch of grown male children. [Source: Wikipedia]

The loud "pops" made by the firing of the shrimp’s pistol claws rival the loudest noises made by sperm whales. They have been called the loudest animals in the ocean. Some places where the shrimp occur overlap with shipping and military areas and the sometimes sometimes interfere with the sonar capabilities of ships and submarines. [Source: Seth Ratliff, Animal Diversity Web (ADW) /=]

Snapping shrimp produce a loud cracking noise by dislocating their claws. When in colonies, they shrimp can interfere with sonar and underwater communication. The shrimp are considered a major source of sound in the ocean. Snapping shrimp produce a noise that is so loud that submarines use the noise to hide from sonar. The shrimp make the noise through "cativation," which is normally produced by the turbulence caused by objects moving extremely quickly through water like the propellor of a submarine. Snapping shrimp have a relatively giant claw that snaps, producing a stream of water that moves at 70 meters per second. The pressure of the water causes tiny bubbles to expand. Within a microsecond the pressure is equalized and the bubbles compress, producing a loud sound and a shock wave, powerful enough to stun prey. Snapping shrimp are heard much than they are observed.

"Pistol shrimp" grow to 3–5 centimeters (1.2–2.0 inches) long. They have a distinctive, disproportionately large claw, larger than half the shrimp's body. The claw can be on either arm of the body, and, unlike most shrimp claws, does not have typical pincers at the end. Rather, it has a pistol-like feature made of two parts. A joint allows the "hammer" part to move backward into a right-angled position. When released, it snaps into the other part of the claw, emitting an enormously powerful wave of bubbles capable of stunning larger fish and breaking small glass jars.

Websites and Resources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Fishbase ; Encyclopedia of Life ; Smithsonian Oceans Portal

Bigclaw Snapping Shrimp

Alpheus cedrici, a strikingly-colored snapping shrimp from Ascension Island, central Atlantic Ocean

Bigclaw snapping shrimp (Scientific name: Alpheus heterochaelis) are native to the western Atlantic Ocean, particularly the Gulf of Mexico. This species is frequently found along the U.S. Atlantic coast from the Outer Banks of North Carolina to the southern tip of Florida. Coastal areas of many islands in the Caribbean also contain populations of bigclaw snapping shrimp, and they have been observed as far south as the Brazilian coast. [Source: Seth Ratliff, Animal Diversity Web (ADW) /=]

Bigclaw snapping shrimp are generally found on the sea bottom in subtidal waters, to a depth of 30 meters (33 meters) or more. They hide or burrow under rocks and shells for protection during the day, and are common on oyster reefs. They can tolerate a wide range of salinity concentrations, from 5-18 parts per thousand (mesohaline) to more than 40 parts per thousand (hyperhaline). You can typically find these shrimp in reefs, other coastal areas, brackish water and relatively shallow sea bottoms. They can also be found in marshes and other wetlands as well as in estuaries. They are particularly fond of habitats rocks, seaweed, and other cover are present, offering them places to hide. /=\

Bigclaw snapping shrimp can live as long as four years in the wild. When kept as pets, these shrimp live an average of 2-3 years. In the wild they have a high rate of larval mortality, as do most shrimp, but the chance of survival increases with age. In studies of the mutualistic relationship between bigclaw snapping shrimp and ninebar prawn-goby (a kind of fish), shrimp in goby-shrimp pairs tended to live longer than shrimp that were not paired with a goby.

Humans utilize bigclaw snapping shrimp for the pet trade, research and education. They have not been evaluated for the International Union for Conservation of Nature (IUCN) Red List. They have no special status according to the Convention on the International Trade in Endangered Species (CITES). Although the abundance and density of bigclaw snapping shrimp have not been extensively studied, their populations are regarded as healthy and stable.

Bigclaw Snapping Shrimp Characteristics

Bigclaw snapping shrimp are the largest of all the snapping shrimp. They range in length from one to 5.5 centimeters (0.4 to 2.2inches), with their average length being three centimeters (1.2 inches). Some adults may only grow to be 10 millimeters in length. Both males and females are roughly equal in size and look similar. They mature at around the approximate size. The only really observable sexually dimorphic trait is that the snapping claw of the male is slightly larger than that of the female [Source: Seth Ratliff, Animal Diversity Web (ADW) /=]

Bigclaw snapping shrimp (Alpheus heterochaelis)

Bigclaw snapping shrimp have three pairs of legs, two sets of antennae, and two claws: a modified snapping claw and an unmodified claw. The side on which the modified claw is found is not specific. It can be on the right side of the left side. Both claws are covered in setae. The coloration of the bigclaw snapping shrimp ranges from dark blue-green to gray. Most shrimp have concentrations of orange on the top of the head behind the eyes, at the tip of the tail, and on the larger, modified claw. Their entire body is speckled with darker gray-brown spots, and much of their body is translucent.

Bigclaw snapping shrimp sense using vision, touch, vibrations and chemicals usually detected with smell, and communicate with vision, touch and chemicals usually detected by smelling. They also use vibrations to communicate. To date, no auditory organs have been discovered in these shrimp despite the big racket they make. Based on this it is assumed that mechanosensory and chemosensory reception are the primary forms of perception. These types of perceptions are particularly important when the snapping shrimp communicate with each other. /=\

By far the most defining characterized of the bigclaw snapping shrimp is its big claw — a large modified snapping pincer. It is capable of being cocked like the hammer of a gun by being opened. This locks the smaller digit of the pincer open by wedging it behind a “shelf” between the digits of the pincer. This pincer can be "fired" by both digits snapping together. This modified pincer occurs only in adult shrimp.

Bigclaw Snapping Shrimp Behavior, Territoriality and Fights

Bigclaw snapping shrimp are nocturnal (active at night), motile (move around as opposed to being stationary), sedentary (remain in the same area) and very territorial (defend an area within the home range). In regard to their home range, they occupy small areas of seabed that are often adjacent to the territories of other bigclaw snapping shrimp. [Source: Seth Ratliff, Animal Diversity Web (ADW) /=]

Bigclaw snapping shrimp have many way of exhibiting territorial defense and because they often occupy territories near other snapping shrimp, territorial intrusions occur quite often and fights often break out. According to Animal Diversity Web: When these interactions occur, they usually begin with a faceoff period between the defending male and the intruding shrimp, whether it be a male or female. During this face-off, the antennae of the animals touch and both animals snap their modified pincer.

Pistol shrimp claw mechanism: 1) closed pistol shrimp claw with slightly hidden plunger (P). 2) Open shrimp claw with exposed plunger (P) and chamber (C). 3) Open shrimp claw with water (W) entering open chamber (C). 4) Closed shrimp claw with plunger (P) pushed into chamber (C), forcing jet stream (J) out of chamber. This last step is what produces the loud noise and strong jet of water

After this initial faceoff, if the interaction is between two males or a defending male currently belonging to a male-female pair and an intruding female, one of the shrimp will become the dominant and the subservient shrimp will retreat. If the interaction is between an unpaired male and unpaired female shrimp, they will often form a monogamous pair. Once dominance has been asserted, the subservient shrimp, if it was the intruder, will retreat back to its original territory; if it was the defending shrimp, it will retreat to find a new territory. These same interactions occur over the protection of mates and eggs or larvae. Chemical signals are also used to mark territory and warn against intruders.

The aggressions of bigclaw snapping shrimp toward members of the same species are expressed with the modified pistol claw. These aggressive interactions are often a result of intrusion upon an occupied dwelling area or hunting ground. They are not life-threatening to either shrimp, but instead warn against some displeasing behavior. When said agonistic intraspecific encounters occur, one shrimp will shoot jets of water toward an intruding shrimp, but will do this within a range that will not allow for formation of a bubble(usually nine or 10 millimeters). At this distance the intruding shrimp is neither killed nor stunned, but only warned that the area upon which he has intruded is occupied./=\

Bigclaw Snapping Shrimp Snapping

According to Animal Diversity Web: The most well-known and studied behavior of bigclaw snapping shrimp is their ability to create loud "pops" with their modified pistol claw. These "pops" are used in communication and during the hunting of prey. This phenomenon is accomplished by the physical process of cavitation, the rapid formation and implosion of cavities in a liquid in which the pressure of the liquid falls below its vapor pressure. [Source: Seth Ratliff, Animal Diversity Web (ADW) /=]

A) Bigclaw snapping shrimp (Alpheus heterochael) is is one of the largest snapping shrimp. The large snapper claw may be either on the right or the left in both sexes. B) Close-up of the snapper claw in its cocked position. The claw is made transparent by the use of methyl salicylate. The claw has a protruding plunger (labeled pl ) on the dactyl ( d ) and a matching socket ( s ) in the immobile propus ( p ) During the extremely rapid closure of the snapper claw a high-velocity water jet is formed when the plunger displaces the water from the propus socket. [Source: Anna S. Von der Heydt, Chemical Engineering Science, January 2003]

The study by Versluis et al. (2000) was the first to describe the physics behind this extraordinary ability. The rapid firing of the modified pincer causes a high-velocity water jet. This water jet exceeds speeds needed for cavitation to occur and causes a very small and very brief bubble to form and implode within an incredibly short time (less than 300 microseconds, a microsecond equals one millionth of a second). A study by Lohse et alia (2001) found that as the bubbles formed by the water jets collapsed, they emitted an intense flash of light. From this they concluded that at the time of the collapse of the cavitations, extremely high pressures (unmeasured) and temperatures (above 5000 °C) occur. These high pressures and temperatures are the cause of the ability to stun prey or even kill them if they are within a few millimeters of the tip of the snapping claw.

The snapping of the modified pistol claw is a primary means of communication. The shrimp use both the snap frequency and the speed of the water jet produced by the snap to receive or transmit information. It has even been suggested by Herberholz and Schmitz (1998) that bigclaw snapping shrimp receiving signals from the claws of other shrimp can detect the sex of the transmitter due to the fact the males produce more “aggressive” snap frequencies and jet speeds. In a similar study, it was found that sex can also be perceived over longer distances (more than 30 meters) by the reception of gender-specific chemical signals. /=\

Bigclaw Snapping Shrimp Food, Predators and Friendly Fish

Bigclaw snapping shrimp are omnivores (animals that eat a variety of things, including plants and animals). They feed on small marine animals including worms, crustaceans, shellfish, and small fish. They also graze on algae. Most of their food is obtained by ambushing their prey and using their snapping claw to create a jet of water that kills or stuns prey.

Bigclaw snapping shrimp are preyed upon by many larger fish including weakfish and red drum. Large fish are not as much by the firepower of the modified pincer. However, these shrimp are not a main food source of any animal.

In areas where predators of bigclaw snapping shrimp are present, the shrimp sometimes form mutualistic relationships with other fish, particularly gobies, namely ninebar prawn-goby (Cryptocentrus cryptocentrus). The gobies and shrimp share burrows.. The gobies benefit by having access to burrows built by the shrimp, and the shrimp benefit by using their antennae to receive tactile signals from the gobies that indicate the presence or absence of predators. /=\

Bigclaw Snapping Shrimp Mating and Reproduction

Bigclaw snapping shrimp are oviparous (young are hatched from eggs) and iteroparous (offspring are produced in groups). They engage in year-round breeding and in internal reproduction in which sperm from the male parent fertilizes an egg from the female parent and employ sexual fertilization in which sperm from the male parent fertilizes an egg from the female parent. The breeding season is every three to five weeks and determined by molt cycles of females. The number of offspring ranges from three to 200. The average gestation period is 28 days and the age in which they become independent ranges from four to five days.[Source: Seth Ratliff, Animal Diversity Web (ADW) /=]

Bigclaw snapping shrimp, like most other snapping shrimp, are monogamous (having one mate at a time). There is a brief period of a few hours directly after the female molts during which they are sexually receptive. Chemical signals and “firings” of the modified pincer signal when she is receptive. The extent of their monogamy is not fully known but more than 65 percent of the shrimp captured in a study by Nolan and Salmon (1970) were in male-female pairs.

According to Animal Diversity Web: Relations of male-female pairs in bigclaw snapping shrimp often begin in a similar manner as territorial interactions between snapping shrimp. Interactions usually begin with aggressive warning snaps produced by the modified pincer until it is determined by both shrimp that they are interacting with a member of the opposite sex. The male-female pair will then mate at the appropriate time in the female’s molt cycle. This time usually occurs every three to five weeks. Between mating times, the male provides protection for the female when she molts and sheds her protective outer covering. This type of male-female pairing benefits the male by allowing access to the maximum number of mating opportunities and benefits the female by making it unnecessary to search for a mate while in her vulnerable molting state. Chemical signals are expected to also play a role in identifying unpaired shrimp.

Bigclaw Snapping Shrimp Development

Bigclaw snapping shrimp eggs and larvae are predominately cared for by the males though the female shrimp is never absent during the larval development of the hatchling shrimp, Pre-birth provisioning is done by females and protecting is done by males. Parental care and pre-independence protection is provided by the male. Male shrimp are more aggressive territorial defenders than female shrimp, and this territoriality causes the males to be more protective of the developing larvae. After 4-5 days, larvae are fully formed and parental protection and care ceases.

After fertilization, the eggs gestate for approximately 28 days and then hatch. According to Animal Diversity Web: After hatching, bigclaw snapping shrimp enter a larval development cycle of metamorphosis consisting of three larval stages. The first stage lasts only 1-2 hours during which enlargement of the organism occurs. Some shrimp are hatched at a large enough body size to begin the second larval stage, skipping the entire first larval stage because it is unnecessary for development. The second larval stage lasts 28 hours and serves to further develop the eyes and appendages of the shrimp. The third and final stage of larval development lasts approximately 2-3 days. [Source: Seth Ratliff, Animal Diversity Web (ADW) /=]

Bigclaw snapping shrimp molt their exoskeletons during larval development. The time of molting depends on the rate of growth of each individual larva. After the third stage of larval development, bigclaw snapping shrimp enter the post-larval stage and resemble adult shrimp without the modified pincer. Until the post-larval stage occurs and functional mouthparts are formed, the larvae feed completely on egg yolk and oil reserves. Although bigclaw snapping shrimp are known to be sexually mature after their post-larval stage, an exact time to reproductive maturity has not been studied.

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated April 2023

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