The Six-lined Racerunner
Described in 1766 by Carl Linnaeus from a type specimen collected by Alexander Garden in Carolina, six-lined racerunners (Aspidoscelis sexlineatus) are a species of lizard endemic to North America east of the Rockies. They belong to a largely tropical and subtropical family of lizards called the Teiidae, a group well represented in the Pampas Amazónicas. Recent studies reported by Science suggest that this species started its evolutionary trajectory some 3 to 7 million years ago. In short, they've been around a long time, a lot longer than us humans. However, like many other species, they have not always been able to adapt to our presence. At least until the 1940s, these lizards could be found in sandy habitats in parts of Washington, D.C. But these habitats have been largely eliminated by development and no racerunners have been reported since, and no one knows, or even seems to care, if they persist there today. Their story will illustrate many aspects of our tremendously poor understanding of biodiversity, nature, and human impacts.
What can we learn from these lizards?
Six-lined racerunners are just one of the approximately 124 species of lizards found native to the United States and are found from South Dakota and Minnesota south to extreme northeastern Mexico, and eastwards to Maryland and the Florida Keys. While considered a common and widespread species overall, they are disappearing in parts of their historic range. In Illinois, Iowa, Kentucky, Maryland, South Dakota, West Virginia, Wisconsin, and Wyoming they are considered vulnerable, imperiled, or critically imperiled, and, in some cases, a species of greatest conservation need by state wildlife action plans. How much do we really know about the species that live around us and the ecosystems that support them and us? These lizards, like most species, have certain habitat requirements and can only adapt "so much" to rapid changes in the landscape. They need sunny places and don't do well in dense vegetation, so they are often associated with areas subject to periodic fires, grazing, or mowing. Where suitable natural habitats are no longer available, they sometimes persist in managed habitats such as clearcut forestry lands and power line, road, and railroad rights of way.
Never heard a of six-lined racerunner? You're not alone!
Chances are, you have never heard of a six-lined racerunner, sandlapper, fieldstreak, or any other name folks have given these lizards. We rarely come across anyone who has, even in places where they are common. Even professional herpetologists (people who study reptiles and amphibians) and state biologists are often unaware of the presence of these lizards in their own backyards. However, chance are, that if you live in much of their range, you might have seen them many times skittering or dashing by without knowing it!
At present, very little ongoing research or conservation efforts focus on these lizards and their habitats, despite recognition of their decline or vulnerability by various state agencies. One reason is that they aren't considered a priority globally or nationally because they are considered widespread and common. Another reason is that even where they are considered to rank among the species of greatest conservation need, resources are limited and must be dedicated to species of higher priority.
This is the case generally for most species and ecosystems - we don't have the time and money to study them, manage them, conserve them... As is the case with the Pampas Amazónicas ecosystems, six-lined racerunners aren't any more or less important than any other species...but we think they are worthy of your attention!
Useful links
Global species accounts, data, and maps for Aspidoscelis sexlineatus
State accounts for Aspidoscelis sexlineatus - a mix of state agency, university, and private sites