Faded rattlesnake, Yellow rattlesnake
The Midget faded rattlesnake (Crotalus concolor) is a venomous pit viper species found in the western United States. It is a small rattlesnake known for its faded color pattern.
The color pattern of this species consists of pinkish, pale brown, yellow-brown, straw-colored, reddish, or yellow-brown ground color, overlaid with a series of brown elliptical or rectangular dorsal blotches. However, most specimens are gray or silvery. In juveniles, the pattern is distinct but becomes faded in adults, almost to the point where it is indistinguishable from the ground color. This has led to the snake sometimes being locally referred to as the "horseshoe rattler." Like all rattlesnakes, the tail ends in a horny rattle, with the number of tail rings indicating the number of molts the snake has undergone.
Midget faded rattlesnakes occur in the United States in the Colorado and Green River basins. This area covers southwestern Wyoming, Utah, and extreme west-central Colorado. These rattlesnakes inhabit high, cold deserts characterized by sagebrush and an abundance of rock outcrops and exposed canyon walls. Juniper woodlands are more prevalent at higher altitudes. Rock outcrops provide escape cover, thermal cover, and hibernacula for these snakes. They can also be found in sagebrush steppes and riparian areas.
Midget faded rattlesnakes often den in groups, sometimes consisting of up to 100 individuals. Females also gather in groups in areas where they bask in the sun and give birth. After emerging from hibernation in April and May, Midget faded rattlesnakes stay near the den entrance for 2-3 weeks before moving to "shedding habitats" with large flat rocks that assist in molting. Gravid females typically move less than 20 m from their hibernaculum upon emergence. Males and non-gravid females, on the other hand, have some of the longest migrations and largest activity ranges reported for rattlesnakes. The snakes have separate winter/spring and summer activity ranges and make shorter, more random movements primarily associated with hunting during the summer. Midget faded rattlesnakes are sit-and-wait predators. Adult individuals hunt in the evening and during the night, while juveniles typically hunt during the day. Midget faded rattlesnakes are peaceful creatures and will defend themselves only if scared or provoked. When disturbed they will take a defensive posture and will rattle their tail. They prefer to escape but if feeling threatened they won't hesitate to strike.
The Midget faded rattlesnake has the most toxic venom of Crotalid venoms, although apparently, considerable variability exists among local populations. It is even one of the most potent venoms found in North America, and according to LD50 studies, the venom is many times more potent than that of an Asiatic cobra. It is characterized by the presence of a presynaptic neurotoxin, referred to as concolor toxin, the amount of which varies in individual snakes. In rattlesnakes, venom is generally categorized into two types: Type I, which has high metalloprotease activity and lower toxicity, and Type II, characterized by high-toxicity neurotoxins. Unlike some other rattlesnakes that undergo an ontogenetic shift in venom composition, the Midget faded rattlesnake does not show significant changes in venom toxicity as it matures. This phenomenon is termed "venom paedomorphosis," where the snake retains its juvenile venom characteristics into adulthood. The venom of this species is particularly potent, being 5-30 times more lethal than that of other Western Rattlesnake species. Human envenomations are rare, likely due to the snake's remote habitat and generally mild disposition. Symptoms of envenomation can include numbness, swelling, loss of balance, vomiting, and more. Treatment with CroFab antivenom is recommended and has been found to be effective even when administered 52 hours post-envenomation.
Midget faded rattlesnakes are carnivores and prey mainly on lizards and small mammals.
Females of this species usually give birth to 3-4 live young. Midget Faded Rattlesnakes often aggregate during gestation, and young snakes stay with their mother for about a week after birth. This behavior is thought to be an adaptation to environmental pressures, enhancing predator defense as well as osmo- and thermoregulation.
The biggest threat to Midget faded rattlesnakes comes from humans who kill them when encountered mainly because of fear.
The total population size of the Midget faded rattles is unknown. Presently, this species is not included in the IUCN Red List and its conservation status has not been evaluated.
