Overview
The Six-lined Racerunner (Aspidoscelis sexlineata) is a slender, lightning-fast whiptail lizard native to open, sun-baked landscapes across the eastern and central United States. Named for the six crisp, light-colored longitudinal stripes running down its back, this agile reptile is renowned as one of the fastest sprinting lizards in North America, clocking speeds that allow it to outrun most natural predators across loose sand.
Biology and Physical Characteristics
Adult Six-lined Racerunners are slender lizards measuring up to 24 cm in total length, with an exceptionally long, whip-like tail comprising more than two-thirds of their body length. The dorsal coloration is dark brown, olive, or jet black, traced by six parallel, sharply defined lines of bright yellow, cream, or white that stretch from the neck to the base of the tail. Mature males in breeding condition display striking turquoise-blue or sky-blue wash across their chin, throat, and flanks.
Behavior and Ecology
Strictly diurnal and thermophilic, Six-lined Racerunners do not emerge until the mid-morning sun warms sandy soils to above 30 degrees Celsius. They forage actively by darting from patch to patch, using their sharp vision and keen sense of smell to hunt spiders, grasshoppers, and beetles. If startled, they sprint away in blinding bursts of speed reaching up to 29 km/h (18 mph), zigzagging into rodent burrows or dense thorny briars.
Conservation and Human Impact
Assessed as Least Concern by the IUCN, the Six-lined Racerunner remains abundant throughout its extensive range. Because it requires open, early-successional sandy habitats, fire suppression that allows dense forest canopies to shade out sunny forest floors can cause localized declines, which prescribed burning programs help reverse.
Interesting Factoid
The Six-lined Racerunner can sprint at speeds of up to 18 miles per hour (29 km/h)—faster than an Olympic sprinter can run relative to its body size—appearing as a blur of yellow stripes across open sand.