Phrynosoma douglassiiPigmy Short-horned Lizard

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Geographic Range

Phrynosoma douglassii is the most widely distributed of the Horned Lizards. There are five subspecies which range from southwestern Canada through the western United States to as far south as central Mexico (Manaster 1997).

Habitat

Phrynosoma douglassii is suited to a wide range of habitats and can even live at altitudes as high as 900-11,300 feet above sea level (Manaster 1997). It can typically be found throughout its range in dry areas and at high altitudes (Pianka and Hodges).

Physical Description

Phrynosoma douglassii achieves a size in the range of 2.5 to 6 inches in length which may vary between subspecies. The size of the subspecies Phrynosoma douglassii brevirostre reflects the sexual dimorphism of the species, with the larger females growing up to 7.7 cm while males only grow to 5.5 cm (Powell and Russell 1983). Color varies depending upon the animal's surroundings, as their color provides them with camouflage. The color generally ranges from red-brown to yellow-grey. Its body is flat, broad, and almost oval shaped. It has a crown of short spines on the back of the head that extend vertically--these are the horns. The dorsal scales are irregular and there is a single row of spiny scales along each side of its body (Pianka and Hodges; University of Texas).

Reproduction

The mating season for P. douglassii extends from April to June. This species is viviparous and the young are born in July or August after three months of development. An average of twenty-three young are born which are offered no parental care beyond birth. The babies are capable of caring for themselves within a few hours of being born. Because they lack well developed horns at birth, the babies are especially vulnerable to predation (Manaster 1997). Viviparity has possibly evolved in response to the dry and cool mountain climate that these lizards inhabit (Pianka and Hodges).

Behavior

Males of this species are territorial and announce their territories with head bobbing displays. If a receptive female enters his territory, the male and female will bob heads briefly and then copulate. Colder weather in mid-October serves as a signal that it is time to prepare for hibernation. The lizards dig an underground burrow where they will stay from November to April (Manaster 1997).

Predator avoidance behavior is accomplished primarily by remaining still and depends largely upon color for camouflage. When encountered by a predator, especially a snake, P. douglassii may inflate the body to appear too large to consume. Some species of Phyrnosoma have the ability to squirt blood from their eyes when startled, which may serve to deter a predator. It is unclear whether Phrynosoma douglassii exhibits this particular behavior (Manaster 1997; Pianka and Hodges).

Food Habits

Phrynosoma douglassii is an insectivore and often considered a dietary specialist with a myrmecophagous diet, or a diet consisting primarily of ants. They are also known to eat a variety of other insects based upon availability, including Coleopterids and Orthopterids. The method of foraging exhibited by P. douglassii is classified as sit-and-wait predation. They are not fast movers and prefer to wait for a prey item to come into their range. They possess uncomplicated homodont dentition which limits their diet to smaller sized prey, such as ants. They will only respond to moving prey items and will consume a variety of prey items dependent upon the local fauna. Due to their larger size, females are able to forage on a broader range of prey sizes than males (Powell and Russell 1983).

Economic Importance for Humans: Positive

Humans do not derive any economic benefit from Phrynosoma douglassii.

Economic Importance for Humans: Negative

Phrynosoma douglassii has no negative effects upon humans.

Conservation Status

Legislation exists in most states to protect Horned Lizards from capture and sale into the pet trade. One obstacle to continued success that P. douglassii faces (as well as other Horned Lizards) is the invasion of some habitat by non-native fire ants. These ants tend to outcompete the natural populations of ants and thus decrease the availability of food (Pianka and Hodges).

Other Comments

Horned Lizards (in general) play an important role in many Native American cultures. The Horned Lizard is often seen as a symbol of strength and important as a symbol for healing (Pianka and Hodges). In Mexico the Horned Lizard is believed to help bring rain (Manaster 1997).

Contributors

Melissa Munger (author), Michigan State University, James Harding (editor), Michigan State University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

native range

the area in which the animal is naturally found, the region in which it is endemic.

References

"Herps of Texas-Lizards" (On-line). Accessed December 10, 1999 at http://www.zo.utexas.edu/research/txherps/lizards/phrynosoma.douglassii.html.

Manaster, J. 1997. Horned Lizards. Austin: University of Texas Press.

Pianka, E., W. Hodges. "Horned Lizards" (On-line). Accessed December 10, 1999 at http://www.zo.utexas.edu/faculty/pianka/phryno.html.

Powell, G., A. Russell. 1983. The diet of the eastern short-horned lizard (Phrynosoma douglassii brevirostre) in Alberta and its relationship to sexual size dimorphism. Can. J. Zool., 62: 428-439.