Bleached Earless Lizard

A white and grey lizard crawls along white sand
The bleached earless lizard has evolved within a short time span to gain the white coloration necessary for survival in gypsum dunes.

NPS Photo

 
One of the most famous inhabitants of White Sands National Monument is the bleached earless lizard (Holbrookia maculata ruthveni). This white lizard is a subspecies of the common lesser earless lizard. The common lesser earless can be found throughout the central and southwestern United States, including most of New Mexico. Unlike its relatives, however, the bleached earless lizard is only found in the White Sands area. Adaptations over the last several thousand years allow the bleached earless lizard to thrive in the white sands dunes, but not in other darker environments.

One of the most notable adaptation that sets the bleached earless lizard apart from other common earless lizard populations is its color. The gypsum dunefield is fairly young in geological terms, only about 7,000 years old. Yet the bleached earless lizard has evolved within this short time span to gain a white coloration necessary for survival in this new environment. Against an all-white background, dark lizards can be seen relatively easily by predators like roadrunners or hawks. As predators targeted darker individuals, lighter individuals survived to reproduce. Over many generations this natural selection resulted in the bleached earless lizard’s unique white coloration.

Bleached earless lizards have two black spots on each side of their abdomens. The lizards are typically around four inches (10.16 cm) long and are believed to live an average of four to five years in the wild. Their bodies and tails are both fairly flat. The term “earless” refers to the lack of external ear openings on the lizards. Despite not having these external openings, the bleached earless lizard does have the ability to hear. The bleached earless lizards eat a wide variety of insects including ants, beetles, bees, wasps, and grasshoppers.

This species is the most active from midspring through early fall. Though they live across the dunefield, these lizards are most often seen by guests at the Interdune Boardwalk area in the mornings. In the heat of the day and late at night, the bleached earless lizards bury themselves in the loose soil for protection and temperature regulation.

These lizards use head bobbing, leg stretching, and body compression as displays when other lizards encroach on their territory or to attract mates during the mating season. The mating season for the bleached earless lizard is from May to July. During this season, the lizards gain slight coloration that signals whether they are receptive to advances or that they have already become gravid. Experiments have shown that males can identify the different colorations and will display to those females who would be most responsive to their attention. Females lay one or two clutches per year. The clutch can be anywhere from one to twelve eggs, but is usually between four to six eggs.

Last updated: January 14, 2017

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