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''Crotalus scutulatus'' is known commonly as the Mohave Rattlesnake. Other common English names include Mojave Rattlesnake Stebbins, R.C. (2003). ''A Field Guide to Western Reptiles and Amphibians''. Boston: Houghton Mifflin & Co. pp. 416–417. Campbell JA, Lamar WW (2004). ''The Venomous Reptiles of the Western Hemisphere''. Ithaca and London: Comstock Publishing Associates. 870 pp., 1,500 plates. . and, referring specifically to the nominate (northern) subspecies: Northern Mohave Rattlesnake and Mojave Green Rattlesnake, the latter name commonly shortened to the more colloquial “Mojave green”. Campbell and Lamar (2004) supported the English name “Mohave (Mojave) rattlesnake” with some reluctance because so little of the snake’s range lies within the
Mojave Desert The Mojave Desert (; ; ) is a desert in the rain shadow of the southern Sierra Nevada mountains and Transverse Ranges in the Southwestern United States. Named for the Indigenous peoples of the Americas, indigenous Mohave people, it is located pr ...
. The spelling of the English name with an “h” has been advocated by multiple authors in recent years for various reasons. The most recent iteration of standard English names for North American reptiles, endorsed by the major herpetological societies in the United States and Canada, concludes that spelling with either a “j” or an “h” is correct, based on “whether the word is used in a Spanish or English context.” Thus, their standard English names list adopted the “h” spelling. ''Crotalus scutulatus'' is a highly
venomous Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...
pitviper (family
Viperidae Vipers are snakes in the family Viperidae, found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, New Zealand, Ireland, and various other isolated islands. They are venomous snake, venomous and have long (relat ...
, subfamily
Crotalinae The Crotalinae, commonly known as pit vipers,Mehrtens JM (1987). ''Living Snakes of the World in Color''. New York: Sterling Publishers. 480 pp. . or pit adders, are a subfamily of vipers found in Asia and the Americas. Like all other vipers ...
) found in the
desert A desert is a landscape where little precipitation occurs and, consequently, living conditions create unique biomes and ecosystems. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the la ...
s of the southwestern
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
and deep into mainland
Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
. It is perhaps best known for producing two distinctly different
venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...
types in different
population Population is a set of humans or other organisms in a given region or area. Governments conduct a census to quantify the resident population size within a given jurisdiction. The term is also applied to non-human animals, microorganisms, and pl ...
s. Two
subspecies In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...
are currently recognized. This account describes the widely distributed nominate subspecies, the Northern Mohave Rattlesnake, ''Crotalus scutulatus scutulatus''. The other subspecies, '' C. scutulatus salvini'', occurs in a relatively small area deep in mainland
Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
.


Type specimen and locality

The type specimen of ''Crotalus scutulatus'' is ANSP 7069, in the collection of the Philadelphia Academy of Natural Sciences (formerly one of two specimens of USNM 5027 at the Smithsonian Institution). The type location is "Fort Buchanan, Arizona". The ruins of Fort Buchanan are in present day Santa Cruz County, Arizona.


Description

''Crotalus scutulatus'' grows to an average total length (including tail) of less than , with a maximum total length of 123.6 cm (4.1 ft) for males and 92.2 cm (3.0 ft) for females. There is no single visual trait that reliably identifies ''C. scutulatus'' and the most reliable visual identifications result from careful consideration of multiple traits. ''Crotalus scutulatus'' is broadly sympatric with '' C. atrox'' (the Western Diamond-backed Rattlesnake), which it closely resembles. The dorsal color of ''C. scutulatus'' varies from shades of green to browns, grays, and even yellowish. ''Crotalus scutulatus'' has a row of large diamond-shaped dorsal blotches closely resembling ''C. atrox'' but lacking the abundant dark speckling, both coarse and fine, found throughout the dorsal surfaces of ''C. atrox''. Additionally, ''C. scutulatus'' lacks the white margins along the caudal edges of the dorsal “diamonds” that are found in most ''C. atrox''. The postocular light facial stripe usually bends toward the neck and does not intersect with the mouth in ''C. scutulatus'', as it does in ''C. atrox''. The tail is usually marked with alternating pale and dark rings in both species, with the dark rings often (but not always) being narrower than the pale ones in ''C. scutulatus'' and the colors are usually less distinct than the bright white and dark black caudal rings of most ''C. atrox''. The proximal rattle segment contains live tissue and is usually bicolor – yellow and black, or entirely yellow, in ''C. scutulatus'', but entirely black (sometimes with a brush of white) in ''C. atrox''. The crown scales (between the supraoculars) of ''C. scutulatus'' are relatively large compared to other rattlesnakes like ''C. atrox'' (but see '' C. molossus'' and '' C. ornatus''), and the enlarged scales spill out behind the supraocular scales in a fan shape, usually with a well-defined margin. The minimum number of scales separating the supraoculars varies from two to four in ''C. scutulatus''. Crown scales on ''C. atrox'' are usually smaller, more numerous, and they do not produce the well-defined fan where they integrate into the scales behind the crown.


Geographic range

This snake is found in arid habitats in the southwestern
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
, from the Mohave Desert in
California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
’s
Los Angeles Los Angeles, often referred to by its initials L.A., is the List of municipalities in California, most populous city in the U.S. state of California, and the commercial, Financial District, Los Angeles, financial, and Culture of Los Angeles, ...
and San Bernardino Counties, across most of western and southern
Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...
(southwest of the
Mogollon Rim The Mogollon Rim ( or or ) is a topography, topographical and geological feature cutting across Northern Arizona, the northern half of the U.S. state of Arizona. It extends approximately , starting in northern Yavapai County, Arizona, Yavapa ...
), and from El Paso County south through the Big Bend region of western
Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...
. It also occurs as far north as Lincoln County in
Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...
, Washington County in southwestern
Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...
, and portions of extreme southern
New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...
. In
Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
, it is found in
Sonora Sonora (), officially Estado Libre y Soberano de Sonora (), is one of the 31 states which, along with Mexico City, comprise the Administrative divisions of Mexico, Federal Entities of Mexico. The state is divided into Municipalities of Sonora, 72 ...
, Chihuahua, and south on the
Mexican Plateau The Central Mexican Plateau, also known as the Mexican Altiplano (), is a large arid-to-semiarid plateau that occupies much of northern and central Mexico. Averaging above sea level, it extends from the United States border in the north to the T ...
to the states of
Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
,
Puebla Puebla, officially the Free and Sovereign State of Puebla, is one of the 31 states that, along with Mexico City, comprise the Federal Entities of Mexico. It is divided into 217 municipalities and its capital is Puebla City. Part of east-centr ...
, and
Veracruz Veracruz, formally Veracruz de Ignacio de la Llave, officially the Free and Sovereign State of Veracruz de Ignacio de la Llave, is one of the 31 states which, along with Mexico City, comprise the 32 Political divisions of Mexico, Federal Entit ...
. It is found in
desert A desert is a landscape where little precipitation occurs and, consequently, living conditions create unique biomes and ecosystems. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the la ...
s and other areas with
xeric Deserts and xeric shrublands are a biome defined by the World Wide Fund for Nature. Deserts and xeric (Ancient Greek 'dry') shrublands form the largest terrestrial biome, covering 19% of Earth's land surface area. Ecoregions in this habita ...
vegetation from near sea level to about elevation. This serpent has also been observed guarding the summit of Black Butte at Mt. Shasta, California.


Habitat

''Crotalus scutulatus'' is primarily an inhabitant of broad
desert A desert is a landscape where little precipitation occurs and, consequently, living conditions create unique biomes and ecosystems. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the la ...
valleys or lower mountain slopes, ''C. scutulatus'' is often found in sparsely vegetated areas containing predominantly
creosote Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood, or fossil fuel. They are typically used as preservatives or antiseptics. Some creosote types w ...
('' Larrea''), sage (''
Ambrosia In the ancient Greek mythology, Greek myths, ambrosia (, ) is the food or drink of the Greek gods, and is often depicted as conferring longevity or immortality upon whoever consumed it. It was brought to the gods in Mount Olympus, Olympus by do ...
''),
mesquite Mesquite is a common name for some plants in the genera ''Neltuma'' and '' Strombocarpa'', which contain over 50 species of spiny, deep-rooted leguminous shrubs and small trees. They are native to dry areas in the Americas. Until 2022, these ge ...
('' Prosopis''), various
cacti A cactus (: cacti, cactuses, or less commonly, cactus) is a member of the plant family Cactaceae (), a family of the order Caryophyllales comprising about 127 genera with some 1,750 known species. The word ''cactus'' derives, through Latin, ...
(
Cactaceae A cactus (: cacti, cactuses, or less commonly, cactus) is a member of the plant family Cactaceae (), a family of the order Caryophyllales comprising about 127 genera with some 1,750 known species. The word ''cactus'' derives, through Latin, ...
), and Joshua trees (''
Yucca brevifolia ''Yucca brevifolia'' (also known as the Joshua tree, yucca palm, tree yucca, and palm tree yucca) is a plant species belonging to the genus ''Yucca''. It is tree-like in habit, which is reflected in its common names. This monocotyledonous tree ...
''), as well as
juniper Junipers are coniferous trees and shrubs in the genus ''Juniperus'' ( ) of the cypress family Cupressaceae. Depending on the taxonomy, between 50 and 67 species of junipers are widely distributed throughout the Northern Hemisphere as far south ...
(''
Juniper Junipers are coniferous trees and shrubs in the genus ''Juniperus'' ( ) of the cypress family Cupressaceae. Depending on the taxonomy, between 50 and 67 species of junipers are widely distributed throughout the Northern Hemisphere as far south ...
us'')
woodland A woodland () is, in the broad sense, land covered with woody plants (trees and shrubs), or in a narrow sense, synonymous with wood (or in the U.S., the '' plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunli ...
and
grassland A grassland is an area where the vegetation is dominance (ecology), dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes such as clover, and other Herbaceo ...
(
Poaceae Poaceae ( ), also called Gramineae ( ), is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos, the grasses of natural grassland and species cultivate ...
) habitats in some places. In general, ''C. scutulatus'' tends to avoid densely vegetated and extremely rocky areas, preferring relatively flat, open, and xeric habitats.


Conservation status

''C. scutulatus'' is classified as Least Concern (LC) on the
IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...
of Threatened Species (v 3.1, 2001). Species are listed as such due to their wide distribution, presumed large population, or because they are unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend was stable when assessed in 2007.


Behavior

''Crotalus scutulatus'' is most active from April to September. They are ambush predators, eating mostly small
rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...
s and
lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...
s. Courtship begins in late summer/fall, is interrupted by winter, and resumes in the spring. Females bear live young, from two to 17 (average about eight), from July through September. Klauber LM (1997). ''Rattlesnakes: Their Habitats, Life Histories, and Influence on Mankind. Second Edition''. First printing in 1972. Berkeley: University of California Press. . This species is not known to den communally and they have no need to seasonally migrate between winter dens and summer foraging areas, as do some other species living at higher elevations and higher latitudes. Instead, individuals occupy well defined
home range A home range is the area in which an animal lives and moves on a periodic basis. It is related to the concept of an animal's territory which is the area that is actively defended. The concept of a home range was introduced by W. H. Burt in 1943. ...
s year around, taking shelter during the winter and hot summer weather in burrows excavated by animals like
rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...
s,
tortoise Tortoises ( ) are reptiles of the family Testudinidae of the order Testudines (Latin for "tortoise"). Like other turtles, tortoises have a shell to protect from predation and other threats. The shell in tortoises is generally hard, and like o ...
s, and kit foxes. Like other rattlesnakes, this species is routinely preyed upon by larger predators like
coyote The coyote (''Canis latrans''), also known as the American jackal, prairie wolf, or brush wolf, is a species of canis, canine native to North America. It is smaller than its close relative, the Wolf, gray wolf, and slightly smaller than the c ...
s,
bobcat The bobcat (''Lynx rufus''), also known as the wildcat, bay lynx, or red lynx, is one of the four extant species within the medium-sized wild cat genus '' Lynx''. Native to North America, it ranges from southern Canada through most of the c ...
s, and raptors. As a result, it is shy, cryptic, and does not seek out confrontations with larger creatures, including humans. But like other rattlesnake species, it will strike and bite vigorously when disturbed, especially if surprised or when there is no nearby vegetation or burrow into which the snake can escape.


Recent genetic and morphological analyses

Robust genetic analyses have revealed the population structure of ''C. scutulatus'' throughout the species' range, correlating genetic evidence of isolation and subsequent secondary contact of subpopulations with corresponding geologic and climatic events. As a result, four genetically distinct clades among present-day ''C. scutulatus'' have been described''.'' The earliest split occurred at the northern margin of the Central Mexican Plateau about 4.1 million years ago (MYA), separating the species into northern and southern subpopulations. Then about 1.8 MYA, the subpopulation now identified as ''C. scutulatus salvini'' diverged genetically from the animals on the Central Mexican Plateau. Most recently, the northern subpopulation was divided at the
Continental Divide A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not ...
(Cochise Filter) about 1.5 MYA, creating the Mojave-Sonoran clade to the west and the Chihuahuan clade to the southeast. Note that the boundaries between these clades correspond to elevational clines where climatic shifts during
Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
glacial advances and retreats likely isolated the subpopulations during cold periods but allowed secondary contact and resumption of
gene flow In population genetics, gene flow (also known as migration and allele flow) is the transfer of genetic variation, genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent ...
during warmer periods, including the present. These analyses indicate that the Central Mexican Plateau clade is more closely related (i.e., more recently shared a common ancestor) to the Huamantlan Rattlesnake (currently ''C. scutulatus salvini'') than it is to the northern (Mojave-Sonoran and Chihuahuan) clades, suggesting that the designation of ''salvini'' as a subspecies of all other ''C. scutulatus'' is problematic. More recently, qualitative, meristic, and morphometric traits from 347 specimens of ''C. scutulatus'' were analyzed, producing the conclusion that the species "is phenotypically cohesive without discrete subgroups, and that
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...
follows a continuous cline in primary color pattern and meristic traits across the major axis of its expansive distribution," suggesting that "multiple episodes of isolation and secondary contact among
metapopulation A metapopulation consists of a group of spatially separated populations of the same species which interact at some level. The term metapopulation was coined by Richard Levins in 1969 to describe a model of population dynamics of insect pests in a ...
s during the
Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
were sufficient to produce distinctive genetic populations, which have since experienced
gene flow In population genetics, gene flow (also known as migration and allele flow) is the transfer of genetic variation, genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent ...
to produce clinal variation in phenotypes without discrete or diagnosable distinctions among these original populations." It was recommended that, for taxonomic purposes, ''Crotalus scutulatus'' "be retained as a single
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
, although it is possible that ''C. s. salvini'', which is morphologically the most distinctive population, could represent a peripheral isolate in the initial stages of
speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...
."


Venom


History

For decades, the bite of ''C. scutulatus'' has been considered to be extraordinarily deadly, often described as the (or “one of the”) deadliest or most dangerous rattlesnakes. For example: "the most lethal of the North American rattlesnake venoms"; "one of the most lethal venoms among the world's reptiles"; "an extremely dangerous snake"; "probably the most dangerous snake in the United States"; and “considered among the most venomous snakes on Earth”. Such claims are usually attributed to the neurotoxin produced by most populations of ''C. scutulatus'' in the United States and Mexico, which has been reported to be capable of causing delayed respiratory paralysis with little or no local tissue injury. This neurotoxin was isolated and described in 1975 and named "Mojave toxin". In 1978, an area in southcentral Arizona was identified where the venom of ''C. scutulatus'' is significantly less lethal to laboratory mice than venom from the balance of the species' range. The more lethal (and more widely distributed) variant was named "venom A" and the less lethal variant was named "venom B". The difference in lethality was later determined to be lack of Mojave toxin in the venom B population. Thus, venom A became known as the neurotoxic variant and venom B became the non-neurotoxic variant. In addition to the absence of Mojave toxin, ''C. scutulatus'' venom B was found to contain tissue-destroying
toxin A toxin is a naturally occurring poison produced by metabolic activities of living cells or organisms. They occur especially as proteins, often conjugated. The term was first used by organic chemist Ludwig Brieger (1849–1919), derived ...
s, predominantly
metalloproteinase A metalloproteinase, or metalloprotease, is any protease enzyme whose catalytic mechanism involves a metal. An example is ADAM12 which plays a significant role in the fusion of muscle cells during embryo development, in a process known as myoge ...
s, similar to the venoms of many other rattlesnakes. Some animals in the
intergrade In zoology, intergradation is the way in which two distinct subspecies are connected via areas where populations are found that have the characteristics of both. There are two types of intergradation: primary and secondary intergradation. Primary ...
zone between venom A and B populations produce venom containing both Mojave toxin and significant metalloproteinase and they have been labeled "venom A+B". Other studies have noted that pitviper venoms can be divided generally into two dichotomous groups that have been termed “toxicity vs. tenderizers” (neurotoxic vs. tissue-destroying, respectively). The more toxic (lethal to lab mice) venoms are dominated by
presynaptic In the nervous system, a synapse is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending o ...
neurotoxin Neurotoxins are toxins that are destructive to nervous tissue, nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insult (medical), insultsSpencer 2000 that can adversely affect function ...
s (of which Mojave toxin is one homolog) but they lack significant amounts of hemorrhagic and tissue-destroying
metalloproteinase A metalloproteinase, or metalloprotease, is any protease enzyme whose catalytic mechanism involves a metal. An example is ADAM12 which plays a significant role in the fusion of muscle cells during embryo development, in a process known as myoge ...
s and serine proteinases, while the “tenderizer” venoms are dominated by the hemorrhagic and tissue-destroying components but contain little or no neurotoxin. In the broader context of all pitvipers, the more common venoms containing higher levels of metalloproteinase and lacking significant neurotoxin have been termed “type I” venoms, while venoms containing high levels of neurotoxin but lacking hemorrhagic and tissue-destroying components are called “type II”. Thus, ''C. scutulatus'' venom A is a type II venom, and venom B is a type I venom.


Mojave toxin

Mojave toxin is a potent
presynaptic In the nervous system, a synapse is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending o ...
β-neurotoxin composed of two distinct peptide subunits.Aird, S.D. et al. (1985). "Rattlesnake presynaptic neurotoxins: primary structures and evolutionary origin of the acidic subunit". ''Biochemistry'' 24: 7054–7058. The
basic Basic or BASIC may refer to: Science and technology * BASIC, a computer programming language * Basic (chemistry), having the properties of a base * Basic access authentication, in HTTP Entertainment * Basic (film), ''Basic'' (film), a 2003 film ...
phospholipase A2 (PLA2) subunit alone is mildly toxic while the
acid An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...
ic subunit is not toxic by itself, but both subunits must be present to constitute Mojave toxin. The basic subunit is present in the venoms of many species of '' Crotalus'', including '' adamanteus'', '' pyrrhus'', ''scutulatus'', ''
tigris The Tigris ( ; see #Etymology, below) is the eastern of the two great rivers that define Mesopotamia, the other being the Euphrates. The river flows south from the mountains of the Armenian Highlands through the Syrian Desert, Syrian and Arabia ...
'', and '' viridis''. The acidic subunit is less commonly distributed and limited to individuals in populations that also express the basic subunit.


Human lethality


Mortality

Mortality statistics have long shown that there are only about 2 to 6 people killed by venomous snakes annually in the United States, with most deaths reported in the southeastern states, despite ''C. scutulatus'' occurring only in the southwest, where they are commonly encountered and responsible for many bites each year. Thus, statistics from both the Centers for Disease Control and the American Association of Poison Control Centers suggest that bites by ''C. scutulatus'' are no more lethal than bites by other rattlesnake species.


Respiratory paralysis

Respiratory paralysis was reported in laboratory animals in the 1930s during comparison of venoms from North American pitvipers, confirming respiratory paralysis and indicating extreme lethality (aka toxicity) in pigeons caused by ''C. scutulatus'' venom. Numerous subsequent studies, mostly using mice, confirmed the relative lethality of ''C. scutulatus'' venom A in laboratory animals. In 1956, Laurence Klauber quoted these studies in his widely-read rattlesnake reference, adding “…if future tests of the quality of the venom of ''C. s. scutulatus'' corroborate the m.l.d. edian lethal dosefigures now available, this may prove to be a very dangerous rattler.” Apparently because of these early animal studies, warnings subsequently abounded about the extreme lethality and danger of respiratory paralysis following bites by ''C. scutulatus''.


Recent clinical studies

Recent investigations of human rattlesnake bites in regions where ''C. scutulatus'' is common have cast doubt on the legitimacy of concerns regarding extreme lethality and respiratory failure/paralysis in humans. A retrospective study of 3440 Arizona rattlesnake bites reported to the Arizona Poison and Drug Information Center (covering all of Arizona except Maricopa County) between January 1999 and December 2020, disclosed no reports of neurotoxic respiratory failure/paralysis. Another retrospective study of 289 rattlesnake bites treated at a tertiary referral hospital in Maricopa County between July 1994 and November 2000, also found no reports of neurotoxic respiratory failure/paralysis. These published findings are consistent with anecdotal reports from southern California, where ''C. scutulatus'' is the predominant biting rattlesnake in the flat creosote bush scrub of the Mohave Desert, where all animals tested thus far have expressed neurotoxic (type II/venom-A) venom, and where
sympatric In biology, two closely related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter each other. An initially interbreeding population that splits into two or more distinct spe ...
''C. atrox'' is not present to confuse snake identification. A literature search for published case reports (that was not limited in scope, either geographically or temporally) revealed only one case of neurotoxic respiratory failure. While the
physiological Physiology (; ) is the science, scientific study of function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a branches of science, subdiscipline of biology, physiology focuses on how organisms, organ syst ...
effects of Mojave toxin are almost certainly dose-dependent, many other variables affect how an organism (pigeon, lab mouse, squirrel, human, etc.) is affected, including such factors as the organism's body mass, age, health, comorbidities,
allergies Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include Allergic rhinitis, hay fever, Food allergy, food al ...
, genetic profile, and many others.


Prognosis of bite victims

While ''C. scutulatus'' is capable of inflicting a life-threatening bite, the prognosis of ''C. scutulatus'' bite victims appears to be no worse than that of victims bitten by other rattlesnakes of similar size. Factors that worsen the prognosis of pitviper bites include delay in reaching advanced medical care, small victim size, and large snake size.


Antivenoms

Both
antivenom Antivenom, also known as antivenin, venom antiserum, and antivenom immunoglobulin, is a specific treatment for envenomation. It is composed of antibodies and used to treat certain venomous bites and stings. Antivenoms are recommended only if ...
s available in the United States are licensed by the
US Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...
for the treatment of bites by all native pitvipers, including
envenomation Envenomation is the process by which venom is injected by the bite or sting of a venomous animal. Many kinds of animals, including mammals (e.g., the northern short-tailed shrew, ''Blarina brevicauda''), reptiles (e.g., many snakes), spiders, i ...
s by ''C. scutulatus''. Each product contains antibodies raised against the venoms of multiple carefully selected pitviper species.
Neurotoxic Neurotoxicity is a form of toxicity in which a biological, chemical, or physical agent produces an adverse effect on the structure or function of the central and/or peripheral nervous system. It occurs when exposure to a substance – specifical ...
''C. scutulatus'' venom is used in the manufacture of CroFab®, while the venom of a tropical rattlesnake ('' C. simus'') that expresses a very similar neurotoxin, is used in the production of Anavip®. Thus, both products are designed to be effective against neurotoxic ''C. scutulatus'' envenomations, and venoms from other species used in the production of both products are protective against type I/venom-B (non-neurotoxic) ''C. scutulatus'' bites.


Subspecies

The
subspecific name In biology, trinomial nomenclature is the system of names for taxa below the rank of species. These names have three parts. The usage is different in zoology and botany. In zoology In zoological nomenclature, a trinomen (), trinominal name, or ...
, ''salvini'', is in honor of English
herpetologist Herpetology (from Ancient Greek ἑρπετόν ''herpetón'', meaning "reptile" or "creeping animal") is a branch of zoology concerned with the study of amphibians (including frogs, salamanders, and caecilians (Gymnophiona)) and reptiles (in ...
Osbert Salvin Osbert Salvin (25 February 1835 – 1 June 1898) was an English natural history, naturalist, Ornithology, ornithologist, and Herpetology, herpetologist best known for co-authoring ''Biologia Centrali-Americana'' (1879–1915) with Frederick DuC ...
. Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). ''The Eponym Dictionary of Reptiles''. Baltimore: Johns Hopkins University Press. xiii + 296 pp. . (''Crotalus scutulatus salvini'', p. 232).


References


External links

*
Mojave Rattlesnake, ''Crotalus scutulatus''
a
AZ PARC
Accessed 3 February 2007.

a
eMedicine
Accessed 3 February 2007.

a
Blue Planet Biomes
Accessed 3 February 2007.

a
Herps of Texas
. Accessed 3 February 2007.

a
Michael Cardwell homepage
Accessed 3 February 2007.

a
Jeff's Big Bend National Park page
Accessed 8 April 2007.
Account of severe ''C. scutulatus'' envenomation
a
venomousreptiles.org
Accessed 6 December 2007. {{Taxonbar, from=Q953286 scutulatus Fauna of the Colorado Desert Fauna of the Mojave Desert Fauna of the Sonoran Desert Fauna of the Chihuahuan Desert Reptiles described in 1861 Taxa named by Robert Kennicott