Overview

Midget Faded Rattlesnakes (Crotalus oreganus concolor) are the smallest member of the western rattlesnake (Crotalus oreganus concolor) species complex with a maximum total length only up to 75 cm, although most individuals measure 45-55 cm. The mass of large adults can reach up to 300 grams, but are generally considerably less than this. There is sexual size dimorphism in both length (males average 44 cm snout-vent length and females 41 cm snout-vent length) and mass (males average 70 g and females 45 g). Midget Faded Rattlesnake coloration and patterning fades with age as the name suggests, but neonates and juveniles can have brighter coloration. Background coloration ranges from cream to yellowish brown to tan with dorsal blotches that are tan to light brown. Blotches tend to be shaped like a rectangle or oval, but can be highly irregular or fused and individuals can be identified by their unique pattern of blotch shapes. Midget Faded Rattlesnakes have a venom composition that is different from all other western rattlesnake subspecies and is one of the most lethal rattlesnake venoms known. This is due to the presence of a neurotoxic element known as concolor toxin. The midget faded rattlesnake was first formally described by Angus Woodbury in 1929 from a specimen in Utah as Crotalus oreganus concolor. The species name “concolor” means uniform color and this represents the tendency for older individuals to attain a faded, uniform color.

Habitat

Midget Faded Rattlesnakes are only found in southwest Wyoming, western Colorado and eastern Utah and their distribution is largely centered on the Green River formation of the Colorado Plateau in these three states. Their range is likely largely limited by geology, as they require exposed rocky outcrops (characteristic of the Green River formation) for denning habitat. These rocky outcrops not only serve as overwintering areas, but are also used for shedding aggregations and for parturition. The snakes use the same specific rocks every year for shedding and parturition. Movement patterns of Midget Faded Rattlesnakes vary by age and reproductive status. Juveniles and gravid females are generally non-migratory and stay nearby the den site. Adult males and non-gravid adult females have much larger movement distances and home ranges and feature disjunct summer and winter ranges. The average distance moved from the denning sites is 779 meters for males and 681 meters for females. Midget Faded Rattlesnakes are limited in their dietary breadth due to their small size. Juveniles feed almost exclusively on lizards with adults shifting to a diet of 80% small mammals and 20% lizards. Adults also will occasionally feed on small birds. Midget Faded Rattlesnakes are a relatively long lived species with low reproductive output. They are ovoviviparous, which means that eggs are retained in the female and young are born live. Age to first reproduction is around five years and mating occurs during July and August after migration from the denning area.

For more information, download the Midget Faded Rattlesnake Fact Sheet