Eastern Fence Lizard

Overview

The Eastern Fence Lizard (Sceloporus undulatus), colloquially celebrated as the prairie lizard, pine lizard, or fence swift, is an agile, rough-scaled diurnal lizard belonging to the spiny lizard family (Phrynosomatidae). Native to the sun-dappled pine woodlands, hardwood ridges, and agricultural edges of the eastern and central United States, this charismatic reptile is renowned for its remarkable bark-like camouflage, lightning-fast tree-climbing agility, and the adult male’s dazzling, iridescent sapphire-blue abdominal patches. Widely studied in evolutionary biology, the eastern fence lizard has become a world-famous textbook example of rapid, real-time natural selection in response to invasive predators.

Ecologically, Sceloporus undulatus serves as an important secondary consumer and insect regulator in temperate forest ecosystems. Foraging actively across tree trunks, rock outcrops, and wooden fences, it consumes immense quantities of forest insects—including pest beetles, caterpillars, and ants. In turn, it represents a crucial food source for a broad guild of woodland predators, including copperheads, black racers, red-shouldered hawks, kestrels, shrikes, and predatory mammals like foxes and raccoons.

Biology and Physical Characteristics

The morphology of the Eastern Fence Lizard is characterized by heavily keeled, overlapping, pointed scales that give its body a distinctly rough, spiny, and bristling texture. Its dorsal coloration is a cryptic mosaic of gray, brown, and charcoal, crossed by a series of dark, wavy, horizontal chevron-shaped bands that mimic the furrowed bark of pine and oak trees with astounding precision. Females possess a dull gray or whitish belly marked with faint gray speckles. In stark, breathtaking contrast, adult males boast vibrant, iridescent electric-blue or turquoise patches bordered by black on both sides of the belly and across the throat; these jewel-like colors reflect ultraviolet light and serve as intense visual signals during territorial disputes and courtship displays.

Behavior and Ecology

Eastern fence lizards are diurnal sun-seekers that spend early mornings basking on elevated wooden fences, fallen logs, or telephone poles to elevate their body temperatures before actively hunting. When an intruder or rival male enters its territory, the resident male displays his dazzling colors by executing rhythmic, rapid ‘push-up’ displays, bobbing his head and compressing his body laterally to flare his brilliant blue throat and belly patches. When threatened by a predator, the lizard darts around to the opposite side of a tree trunk with squirrel-like cunning, circling the bark to keep the trunk between itself and the threat. In a celebrated evolutionary breakthrough, biologists discovered that southern populations of fence lizards invaded by non-native red imported fire ants (Solenopsis invicta) have evolved longer hind legs and a novel behavioral twitching dance to kick off attacking ants, physically adapting to an invasive species in just a few decades.

Conservation and Human Impact

Sceloporus undulatus is classified as Least Concern on the IUCN Red List, supported by vast, resilient, and stable populations across its eastern North American range. It thrives in open, managed pine plantations, national forests, and rural homesteads where fallen timber and wooden split-rail fences provide ideal basking and hunting perches. Localized threats include the clearing of mature pine-oak forests, domestic cat predation, and the over-application of broad-spectrum insecticides that eliminate its invertebrate prey base. Preserving deadwood snags and open woodland canopies remains the cornerstone of its conservation management.

Interesting Factoid

When attacked by invasive, venomous fire ants, the fence lizard does a frantic body-shaking dance: scientists discovered it has evolved longer legs in just a few generations specifically to kick biting fire ants off its skin in under a second.