NIGHT LIZARDS: Xantusiidae

PHYSICAL CHARACTERISTICS

The night lizards are mainly small lizards without the working eyelids that many other species of lizards have. Instead, the night lizards have a see-through scale covering the eye. This clear scale, which looks somewhat similar to a person's contact lens, is called a spectacle. Beneath the spectacle, the eyes of some species of night lizards have catlike pupils, but others have round pupils. The typical night lizard has a low flat body, which allows it to sneak easily into cracks of rocks or into narrow openings between plant leaves.

The bodies of these lizards are covered with small scales, except on the head and belly. The top of the head is covered with large plates, and wide rectangular scales stretch across the belly. Most have drab-colored bodies, usually brown or gray, but a few have striking patterns. The granite night lizard, for example, has a spotted leopard-style pattern of brown spots on an otherwise yellowish body. Some have round and bumpy scales that give the lizard's back the look of a tiny beaded purse. Some night lizards are quite small, reaching only 1.5 inches (3.7 centimeters) long from the tip of the snout to the vent, a slit-like opening at the beginning of the tail and on the underside of the lizard. Adults of the largest species, the yellow-spotted night lizard, grow to more than three times that size, reaching 5 inches (12.7 centimeters) long from the snout to the vent. The typical night lizard has a tail as long or slightly longer than its body.

GEOGRAPHIC RANGE

Night lizards live in the United States, Cuba, and Mexico, as well as in Central America as far south as Panama.

HABITAT

Each night lizard species is very picky about where it makes its home. Some species live only in very dry areas, like rocky deserts. Others only live in the rotting parts of certain types of plants or in the dead leaves or decaying logs laying on the ground in a rainforest. Some night lizards even prefer life in a cave. Although members of the family live in North America, Central America, and Cuba, they stay in small areas within that range. For example, the only part of the United States that is home to night lizards is the Southwest, and the Cuban night lizard makes its home in a tiny part of Cuba, where it lives under rocks or buried in soil in areas of dry warm forest.

DIET

Many night lizards, like the Cuban night lizard, eat insects and spiders. The yellow-spotted night lizard also eats scorpions and other invertebrates (in-VER-teh-brehts), which are animals without backbones. Others, such as the island night lizard, eat at least some seeds and other bits of plants. Scientists are unsure if any species are strict vegetarians that eat only plants. Species in this family search for food where they live. For example, a yellow-spotted night lizard that lives in rotting logs usually looks there for its next meal.

BEHAVIOR AND REPRODUCTION

People rarely see night lizards during the daytime, but they actually can be active both night and day, if the daytime temperatures are not too hot. Even on the best of days, however, they spend most of their time out of sight under dead leaves, inside plants, or in the cracks of rocks. They are much more likely to venture outside at night, when they may scramble about under the cover of darkness. Scientists still know very little about the behavior of night lizards.

NIGHT LIZARD CONFUSION

To figure out how closely some animals are related to other animals, scientists can look at a number of characteristics, such as certain bones that are alike or different. Sometimes scientists find it difficult to decide on the closest relatives of species, including the night lizards. The species in this family have characteristics that are similar to four different families: the geckos, the skinks, the whiptails and tegus, and the wall and rock lizards. So far, scientists have not decided for sure which family the night lizards are most like. They do agree, however, that the night lizard family is an ancient one that dates back more than fifty million years.

Females of all night lizard species, except one, give birth to baby lizards. The typical litter holds five to eight babies. The Cuban night lizard is the only species in this family that lays eggs. The female lays a single egg at a time, dropping it into a hole. The egg hatches two months later.

In most lizard species, a female becomes pregnant only after she mates with a male. Some night lizards do not follow this rule, and the females can become pregnant on their own. Among female yellow-spotted night lizards, some mate with males to become pregnant, but others may not even see males. Some groups of yellow-spotted night lizards that live in Costa Rica and Panama are made up of only females. With no males in sight, the females are able to become pregnant themselves and have perfectly healthy babies.

NIGHT LIZARDS AND PEOPLE

Although some people believe they are venomous, night lizards are not. They are harmless to humans.

CONSERVATION STATUS

According to the World Conservation Union (IUCN), one species of night lizard is Vulnerable, which means that it faces a high risk of extinction in the wild. The U.S. Fish and Wildlife Service lists the same species, the island night lizard, as Threatened, which means that it is likely to become endangered in the foreseeable future. The island night lizard is at risk because people have brought pigs and goats to the three small Channel Islands where the lizard lives. These much larger animals eat the plants that the lizards use as their homes. Efforts are now under way to remove pigs and goats from at least one of the three islands. Although no other species have been named as being at risk, many night lizards are threatened by habitat destruction. When humans cut down rainforests, remove plants, or otherwise destroy the places where the lizards live, whole populations of these animals can disappear.

DESERT NIGHT LIZARD (Xantusia vigilis): SPECIES ACCOUNT

Physical characteristics: Among the smallest species in this family, the desert night lizards grow to only 1.5 inches (3.7 centimeters) long from the tip of the snout to the vent. Like other night lizards, they have no working eyelids. This lizard usually has dark spots on its brown back, although in some areas, the back may have a green, yellow, or orange tint. Its skin is typically wrinkly on the neck and along the sides of the body.

Geographic range: This species makes its home in small areas within the southwestern United States and northwestern Mexico.

Habitat: The desert night lizard also goes by the common name yucca night lizard, because it spends much of its time in clumps of rotting yucca (YUCK-uh) plants. It also lives in old, dead agave (uh-GA-vee) plants.

Diet: The desert night lizard eats ants and beetles and occasionally some other insects that it finds in the plants where it lives.

Behavior and reproduction: This lizard likes to stay hidden in yucca or agave plants. Males and females mate in late spring, and about three months later, the females have their young. The typical brood includes one to three baby lizards. Sometimes, if the weather is especially dry, females may skip a year between births.

Desert night lizards and people: Although desert night lizards can be very numerous in some places, with twelve thousand individuals in an area of just one square mile (or four thousand in a square-kilometer area), people rarely see this shy lizard. Humans can, however, harm the lizard populations by cutting down and removing yucca and agave plants, which often happens when they clear land to make way for houses.

Conservation status: This species is not considered endangered or threatened. ∎

FOR MORE INFORMATION

Books:

Alvarez del Toro, M. Los reptiles de Chiapas. 3rd edition. Chiapas, Mexico: Instituto de Historia Natural, Tuxtla Gutierrez, 1982.

Behler, John, and F. Wayne King. "Night Lizards Family (Xantusidae)" National Audubon Society Field Guide to Reptiles and Amphibians. New York: Alfred A. Knopf, 1979.

Campbell, J. A. Amphibians and Reptiles of Northern Guatemala, the Yucatan, and Belize. Norman: University of Oklahoma Press, 1998.

Estes, R. Sauria terrestria, Amphisbaenia. Vol. 10A, Handbuch der Palaeoherpetologie. Stuttgart: Gustav Fisher Verlag, 1983.

Halliday, Tim, and Kraig Adler. The Encyclopedia of Reptiles and Amphibians. New York: Facts on File, 1986.

Mattison, Chris. Lizards of the World. New York: Facts on File, 1989.

Mautz, W. J. "Ecology and Energetics of the Island Night Lizard, Xantusia riversiana, on San Clemente Island." In Third California Islands Symposium: Recent Advances in Research on the California Islands, edited by F. G. Hochberg. Santa Barbara: Santa Barbara Museum of Natural History, 1993.

Web sites:

"Family Xantusiidae (Night Lizards)." Animal Diversity Web. University of Michigan Museum of Zoology. http://animaldiversity.ummz.umich.edu/site/accounts/classification/Xantusiidae.html (accessed on November 15, 2004).

"Granite Night Lizard." Western Ecological Research Center, U.S. Geological Survey Biological Resources Division. http://www.werc.usgs.gov/fieldguide/xahe.htm (accessed on November 15, 2004).

"Island Night Lizard." eNature. http://www.enature.com/fieldguide/showSpeciesSH.asp?curGroupID=7&shapeID=1059&curPageNum=50&recnum=AR0662 (accessed on November 16, 2004).

"Night Lizard." Wikipedia, the free encyclopedia. http://en.wikipedia.org/wiki/Xantusiidae (accessed on November 15, 2004).