[4] Crotalus scutulatus is a highly venomous pitviper (family Viperidae, subfamily Crotalinae) found in the deserts of the southwestern United States and deep into mainland Mexico.

Additionally, C. scutulatus lacks the white margins along the caudal edges of the dorsal “diamonds” that are found in most C. atrox.

[15][8] This snake is found in arid habitats in the southwestern United States, from the Mohave Desert in California’s Los Angeles and San Bernardino Counties, across most of western and southern Arizona (southwest of the Mogollon Rim), and from El Paso County south through the Big Bend region of western Texas.

[6] Crotalus scutulatus is primarily an inhabitant of broad desert valleys or lower mountain slopes, C. scutulatus is often found in sparsely vegetated areas containing predominantly creosote (Larrea), sage (Ambrosia), mesquite (Prosopis), various cacti (Cactaceae), and Joshua trees (Yucca brevifolia), as well as juniper (Juniperus) woodland and grassland (Poaceae) habitats in some places.

In general, C. scutulatus tends to avoid densely vegetated and extremely rocky areas, preferring relatively flat, open, and xeric habitats.

Instead, individuals occupy well defined home ranges year around, taking shelter during the winter and hot summer weather in burrows excavated by animals like rodents, tortoises, and kit foxes.

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.

[22] 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 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 metapopulations during the Pleistocene were sufficient to produce distinctive genetic populations, which have since experienced gene flow 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, 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.

[27] 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.

[30][31][32][33][34][35] 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).

[36] The more toxic (lethal to lab mice) venoms are dominated by presynaptic neurotoxins (of which Mojave toxin is one homolog) but they lack significant amounts of hemorrhagic and tissue-destroying metalloproteinases and serine proteinases, while the “tenderizer” venoms are dominated by the hemorrhagic and tissue-destroying components but contain little or no neurotoxin.

The basic subunit is present in the venoms of many species of Crotalus, including adamanteus, pyrrhus, scutulatus, tigris, and viridis.

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.

[47] 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.

[48] 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 C. atrox is not present to confuse snake identification.

[49] While the physiological 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, genetic profile, and many others.

[50][47] Both antivenoms available in the United States are licensed by the US Food and Drug Administration for the treatment of bites by all native pitvipers, including envenomations by C.