Pictured above: A female racerunner on the upper-left, and males on the upper-right and bottom. Notice the blue/green tinge around the head of the male. The individual on the upper-right was found under a piece of metal, while the one on the upper-left was in an open grassland.
Description: The prairie racerunner is a small, fast-moving lizard, that will attain adult sizes of about 6 to 10 inches (total body length), and 3 to 4 inches (excluding the tail). They are slender bodied lizards with long tails and 6 distinct stripes that run laterally (3 on each side). These stripes tend to be yellowish over a dark gray or brown background. During the breeding season, the heads and necks of male racerunners turn a very vibrant greenish, or blue-ish color. Aside from the 6 stripes that run laterally, many of these lizards also have a thicker stripe running down the center of their backs that is brownish in color. They are members of the taxonomic order Squamata, sub-order Lacertilia, and members of the taxonomic family Teiidae. Members of the genus Cnemidophorus are often called "whip-tailed lizards" due to their long slender tails.
Habitat/Ecology: Prairie racerunners are found mostly on dry or mesic prairie-type habitats with sandy soil, and sparse or patchy vegetation (such as blue-stem) where they hunt insects and other invertebrates. Because prairies are disappearing within Wisconsin, this lizard has become restricted to small, fragmented prairie remnants and "goat prairies" that exist along bluff sides (which is where they are encountered in the La Crosse area). Traditionally, this lizard was found throughout Wisconsin in the same types of habitats that Ornate Box Turtles (another vanishing species) once enjoyed. They are known to live in self-excavated burrows, or many inter-connected tunnels, in sandy or loamy soil. These they use to escape predators, such as racers (Coluber constrictor) and birds.
I have more frequently encountered this lizard in habitats with very sparse vegetation and between pockets of open sand. I cannot be certain whether this is the result of the species actually preferring this type of habitat, or the fact that a small lizard may be harder to see in thicker vegetation and, thus, the paucity of reports that describe racerunners in such a habitat is the result of a collecting bias. Yet, anyone who has seen a racerunner knows that they are not particularly quiet when making their hasty getaways. Therefore, once one knows what to listen for, the sound of a fleeing racerunner is quite obvious, and can potentially be heard in both sparse and dense vegetation. I can say with a fair amount of certainty that I have rarely heard them in habitats with thick undergrowth or vegetation and, although I have nothing but anecdotal evidence to back this up, I'd surmise that they prefer sparse vegetation with areas of open sand/dirt.
These lizards are fond of warmer temperatures. In fact, I have found them basking on sand that exceeded 35-45 degrees Celsius! I also find them in the shade of a small clump of vegetation that is surrounded by scorching hot sand. I find this behavior interesting because, by doing this, they have essentially decided to rest in a cooler microhabitat that acts as an island surrounded and protected from ectothermic predators (such as racers) by treacherously hot terrain. I often wonder if this is an adaptation that aids in the avoidance of such predators. This statement, however, is conjecture on my part, but is a research question that I'm considering pursuing in the near future.
Due to their affinity for warm temperatures, emergence from hibernation usually occurs later than many other herps found in the same area (late May), and breeding begins when temperatures rise. Racerunners are normally active for a short period during the year, and generally return to their burrows for hibernation by late August. The latest that I've witnessed active adults in the field has been August 29th. Juveniles, however, tend to remain above ground slightly longer. I have seen them active as late as September 8th.
Remarks: Racerunners are aptly named. Usually, one only gets a glimpse of these fleet lizards as they scurry across the sand and into a nearby burrow. They are one of the few species of lizards that exist within Wisconsin, and for that reason it's a great surprise to ever see one. I have encountered them under pieces of wood and metal in prairie preserves (not in La Crosse Co.), and along open bluffsides near La Crosse (where they are very hard to catch).
Until recently, this lizard was described as the Six-lined racerunner (Cnemidophorus sexlineatus sexlineatus), but has now been re-classified as the prairie racerunner (Cnemidophorus sexlineatus viridis).
Above: a juvenile racerunner. Note how small this little fella is. Also note the bright blue coloration of the tail, which is readily broken off as a predator avoidance mechanism.