With no outlet to the sea, dissolved gypsum from the nearby San Andres and Sacramento Mountains once flowed into the Tularosa Basin where it dried, leaving an alkali flat of gypsum crystals known as selenite. Broken down by weathering, the vast fields of selenite produced gypsum particles the size of grains of sand, forming a 275-square-mile field of drifting dunes, 40 percent of which is within the grounds of White Sands National Monument in New Mexico.

Over generations, many of the animals living among the white gypsum dunes adapted to the harsh conditions by developing a lighter coloration. One theory about the prevalence of lighter-colored moths in the sandy, white dunes is that light-colored animals are less visible to predators, avoiding being eaten more often than their darker relatives. With more pale-colored survivors alive to reproduce, the ratio of dark to light members of a species gradually shifts so that most, if not all, of the animals are light in color. Another example is the bleached earless lizard (Holbrookia maculata ruthveni), a pale resident of the white dunes whose relatives living elsewhere are darker in color.

A second theory about the high number of light-colored animals in dunes of White Sands is that something in the soil chemistry affects the animals’ metabolisms, causing the creatures to appear lighter.

Are Invertebrates Living Among the Dunes Also Pale?

Prior to 2006, little was known about the invertebrate denizens of the white dunes. Invertebrates (animals without backbones, such as insects) are important research subjects. Easy to collect and study, insects are like the canary in the mine, telling us when conditions in a region are healthy and warning us when they are not.

In 2006, scientist Eric H. Metzler was awarded a Western National Parks Association research grant to help fund his inventory of Lepidoptera (the scientific order that includes moths and butterflies) within and adjacent to the white gypsum dunes.

Metzler and his colleagues have recorded more than 600 species of moths in and near the dunes, including at least 26 previously undiscovered moth species. According to Metzler, about 50 percent of the newly discovered moth species are white or display faded colors.

Metzler’s inventory will provide a baseline against which scientists can measure the effects of climate change, air pollution, water supply, and many other environmental factors. In the course of his research, Metzler might even solve the mystery of the pale moths.