Sceloporus occidentalis

Western Fence Lizard (Sceloporus occidentalis)

The western fence lizard, scientifically known as Sceloporus occidentalis and often called the blue-belly, is a widespread and common reptile native to the western United States and northern Mexico. Its presence spans a diverse range of habitats, from arid grasslands and sagebrush plains to woodlands and even suburban yards, making it a familiar sight for many in its native territory.

Identification and Characteristics

Adult western fence lizards typically measure between 5.7 to 8.9 centimeters in snout-to-vent length, with a total length reaching about 21 centimeters. Their coloration varies from brown to black, often with sandy or greenish hues, and they possess distinctive black stripes along their backs. The most striking feature, particularly in adult males, is the bright blue coloration of the ventral abdomen, which gives them their common name. This blue is often accompanied by yellow on the underside of the limbs, and males may also display blue patches on their throats and iridescent turquoise spots dorsally. Females and juveniles display a less vibrant coloration.

Habitat and Distribution

The species is found across California, which forms the core of its range, and extends into eastern and southwestern Oregon, Washington (north of Seattle), southwestern Idaho, Nevada, western Utah, northwestern Baja California, New Mexico, and Arizona. They occupy a broad spectrum of elevations and environments, including grassland, chaparral, sagebrush, woodland, coniferous forest, and farmland, generally avoiding extreme desert conditions and often being found near water sources. Urbanization has also led to their adaptation to man-made environments.

Behavior and Diet

Western fence lizards are diurnal, meaning they are active during the day. They are frequently observed basking on surfaces like rocks, paths, and fences to regulate their body temperature. Notably, they can change their skin color to nearly black during basking to absorb more heat. During the winter, they undergo a period of brumation. Their diet consists almost exclusively of terrestrial invertebrates, with insects forming the primary food source, supplemented by spiders, isopods, and other small arthropods. Males are territorial and engage in displays, including "push-ups," to defend their home ranges from rivals and attract females.

Reproduction and Ecology

Reproduction typically occurs in the spring, with mating taking place after the lizards emerge from brumation. Females lay clutches of three to 17 eggs, usually around eight, in nests dug under surfaces, between April and July. The eggs hatch approximately 60 days after being laid. An interesting ecological role of the western fence lizard is its contribution to reducing the prevalence of Lyme disease. A protein in their blood is toxic to the bacterium that causes Lyme disease, effectively clearing the infection in ticks that feed on them.

Conservation and Urban Adaptation

The western fence lizard is currently listed as unprotected, with no specific conservation restrictions applied. However, urbanization poses a significant threat through habitat loss. Studies indicate that lizards in urbanized areas have evolved shorter limbs and toes, adapting to navigate a greater variety of surfaces. Increased temperatures in urban heat islands also influence their physiology, leading to changes in scale size and number to mitigate heat load and water loss.