EPOW - Ecology Picture of the Week

Mojave Rattlesnake (Crotalus scutulatus)
Southern Arizona, USA

Explanation:  Watch where you step.  This common inhabitant of deserts and grasslands of southwestern U.S. and Mexico has a venom that is more potent than that of its Western Rattlesnake cousin.  This is the Mojave Rattlesnake.    

Largely nocturnal, this beautiful serpent is more concerned with avoiding danger than confronting it.  When startled, it rattles its tail and raises up to a warning posture, but generally retreats rather than strikes, saving its venom for its prey ... rodents, lizards, frogs, and even birds.  But should it strike, it can inject a large dose of venom with potentially deadly neurotoxins.  

Different populations of the Mojave Rattlesnake are known for their variations in the amount and kind of venom.  Two kinds of venom -- Type A and Type B, and intergrades -- are known from this species.  Type A venom is more lethal and contains Mojave (Mohave) toxin which can cause deadly neurotoxic effects (destroying nerve tissue), although Type B venom can cause local proteolytic (breaking down of proteins) and hemorrhagic (profuse bleeding) injury.  In the U.S., Type A Mojave Rattlesnakes occur in southern California, Nevada, Utah, Arizona, Texas and New Mexico.

Update:  Thanks to EPOW reader Brendan O'Connor for pointing out the apparent oddly dark coloration of this species for southern Arizona.  I do need to clarify that this was a specimen held in the Arizona Sonora Desert Museum outside of Tucson.