The Six-lined racerunner (Aspidoscelis sexlineatus ) is a species of lizard native to the United States and Mexico.
Six-lined racerunners are typically dark green, brown, or black in color, with six yellow or green-yellow stripes that extend down the body from head to tail. The underside is usually white in color in females and pale blue in males. Males also sometimes have a pale green-colored throat. They are slender-bodied, with a tail nearly twice the body length.
Six-lined racerunners are found throughout much of the southeastern and south-central portion of the United States, from Maryland to Florida in the east, across the Great Plains to southern Texas and northern Mexico. Their range also reaches north to Wisconsin and Minnesota. A small disjunct population is found in Tuscola County, Michigan. These lizards live in a wide variety of habitats including grasslands, woodlands, open floodplains, or rocky outcroppings. They prefer lower elevations, with dry loamy soils; in such areas, they are often found in human-made disturbances like under voltage towers or along highways and railroads.
Six-lined racerunners are solitary and territorial creatures. They are most active in the morning and spend nights inside their burrows. They are wary, energetic, and fast-moving, reaching speeds of up to 18 mph (29 kmph), darting for cover if approached. Aggressive behavior is common, as the dominant will chase the subordinate and often follow up with a bite to signify dominance. Six-lined racerunners hibernate during cold months of the year and are active from April through early October.
Six-line racerunners are carnivores (insectivores). Their diet includes spiders, grasshoppers, and large insects.
Six-lined racerunners are polygynandrous (promiscuous) meaning that both males and females have multiple partners each mating season. Breeding usually takes place in the spring and early summer. During this time males perform an act termed "female tending" where the male will repeatedly charge at a female trying to leave its burrow until the female allows for the male to approach and begin the reproductive process. The clutch size is up to 6 eggs which hatch in 6 to 8 weeks. A second clutch of eggs may be laid several weeks after the first. The eggs are usually laid in a nest dug in soft soil or under logs. The hatchlings are independent at birth and don’t require parental care. They become reproductively mature at the age of one year.
There are no major threats to this species at present. Locally, some populations suffer from the loss of their native habitat for human uses.
According to IUCN Red List, the total population size of the Six-line racerunner is unknown but probably exceeds 1,000,000 individuals. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.
