Plestiodon obsoletus

Geographic Range

The biogeographic range of Eumeces obsoletus (Great Plains skinks) begins in western Missouri and northwest Arkansas and extends to eastern Arizona. It reaches as far north as the southern portions of Nebraska and ends in northern Mexico. They are found in Nebraska, Colorado, Arizona, New Mexico, Texas, Oklahoma, Kansas, Missouri, and Arkansas. They are only found in the Nearctic region and specifically in the southern half of the North American Grassland Biome. Eumeces obsoletus are most abundant in Kansas. Scattered populations are found in more northern portions of Nebraska, Iowa, and Missouri but are not connected to the main distribution. Lack of rocks coupled with a decrease of mean daily temperatures has limited distribution around these isolated populations.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Great Plains skinks are found in wide and diverse habitats including mixed woodland, prairies, forests, mountain slopes, canyons, open hillsides and deserts. In the southwest, they are confined to rugged rocky terrain. Areas that have short, thick grass or other ground vegetation, and flat rocks for shelter are optimal habitats for Great Plains skinks and they are found in dense low vegetation near rock outcroppings, or beneath trash and rocks. If rocks or other surface cover are absent they will burrow in the open or use small mammal burrows for shelter

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• forest forest
• mountains mountains

Physical Description

Great Plains skinks are larger than other species of skinks with a relatively thick torso and neck. The neck is muscular and equals the body in diameter. They have long, curved claws and their toes and feet are covered in scales. Great Plains skinks do not have the traditional striped pattern of most skinks , and their scale patterns have changed to an oblique pattern rather than the normal parallel pattern. The coloring is a mottled light grey, dark brown, and black. Males also have a patch of orange on either side of their head.

• Sexual Dimorphism
• male larger
• sexes colored or patterned differently
• male more colorful

Development

After eggs are laid they take about 40 days to hatch. Hatching occurs in late summer and first hibernation begins in October of the same year. Juvenile Eumeces obsoletus are black with a vibrant blue tail. They do not display the mottled, tri-color pattern until adulthood. Because of this trait, scientists considered juveniles a different species for many years: Eumeces guttulatus . By the time the skinks reach one full year of age, they are nearing adult size, coloring, and reproductive maturity. They can live for up to eight years.

Reproduction

Mating pairs may be found under rocks during breeding season, but they are a polygynandrous species. Sexual activity is limited to a period of a few weeks in late spring and the mating pattern followed is similar to other species of Eumeces . The male recognizes the female due to her scent and lack of orange markings on the head. The male chases the female, nips at her tail, and catches her by her neck skin. The male loops underneath the female to begin copulating. Copulation lasts around 6 minutes.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Mating occurs in late April and early May, eggs are laid in early June and hatch in about 40 days. Great Plains skinks produce large clutches of 7 to 24 eggs. Only 8% of lizard species have larger average broods than this Great Plains skinks. Large clutches compensate for the long amount of time required to incubate the eggs and because they may not reproduce every year. The mother guards the eggs for a 1 to 2 month incubation period. No more than 1 clutch per year is possible and some females do not breed every year. Older females are more productive than young ones (as in many other species of lizard). Environmental factors may also influence clutch size. If the weather is dry females will change nesting sites. If eggs are already laid, she will dig up the soil around them to increase humidity. Females are known to release water from the bladder to moisten the nest cavity if necessary. When the eggs hatch, the mother smells around the eggs to locate eggs that are not yet hatched. She passes her head over babies left to right and rouses the recently hatched skinks. She grooms babies for ten days after birth by licking their cloacal vent around 5 times for about half a second. Hatching occurs in the late half of the summer and mortality of young is high. By the time the skinks reach one full year they are nearing adult size.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• sexual sexual
• oviparous oviparous

The mother spends the entire summer sheltering and guarding her eggs before they hatch. Following birth, the mother cares for the young and is extremely tolerant of them. Males give no care to young.

• Parental Investment
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

Great Plains skinks can live up to 8 years in the wild. The population has a sharp decrease in frequency of skinks that survive from age 1 to 2 and there are large drops in the frequency of older skinks that levels off around year 5.

Behavior

Great Plains skinks are never found far from their rocky homes. This is presumably due to the temperature extremes in their environments. In field research it has been found that activity level drastically drops off when the temperature rises. This species of skink does not tolerate cold temperatures either. Beginning in October Great Plains skinks hibernate until March of the next year.

• Key Behaviors
• terricolous
• diurnal diurnal
• sedentary sedentary
• hibernation hibernation
• aestivation
• solitary solitary

Home Range

Great Plains skinks stay close to their burrows and have a small hunting range. They may spend many days under the same rock or in their burrow. When a skink does emerge, it only makes short trips and returns to its home. Burrows are temporary and the skink may change its burrow location every few days or weeks, depending on environmental conditions. When the skink does change the site of its burrow it is often only a few meters away from the original burrow.

Communication and Perception

Great Plains skinks use visual cues and their sense of smell to discriminate the sex of other skinks at a distance. After contact is made, communication is through touch and smell.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

In the wild, Great Plains skinks consume only invertebrates. Their diet consists of insects, arachnids, arthropods, and gastropods. There have rarely been remains of other skinks in the stomachs of Great Plains skinks, but it is believed that this is mostly due to accidents. Most frequently, the remains of gryllid crickets , short-horned grasshoppers , scarabaeid beetles , lepidopteran larvae , and carabid beetles are found in their stomachs. Most prey is found in the sheltered areas near the burrow and many prey species can be found underground. They rely on their sense of smell to find prey and to avoid venomous species. Invertebrate prey generally not consumed include earthworms, centipedes, ants, and cockroaches. Their diet changes seasonally with available arthropod prey.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore
  • eats non-insect arthropods

• Animal Foods
• insects
• terrestrial non-insect arthropods

Predation

Great Plains skinks are preyed on by venomous snakes, birds of prey, and small mammals. Snakes find and trap the skinks in their burrows. Small, fossorial mammals also find skink burrows and prey on them. Most adult Great Plains skinks have scars from predators but they will aggressively defend themselves. They use hard wriggling bites that cause lacerations and defecation as a defense mechanism. When a Great Plains skink bites, it uses its powerful jaws to grab a small piece of skin. It will then thrash around until it leaves a painful laceration. Great Plains skinks are also relatively cryptically colored in their native environment.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Great Plains skinks are a food source for their predators and help control insect and other invertebrate populations in their environment. Parasitic species that use Eumeces obsoletus as a host include four species of chigger. Compared with other species of skinks, Eumeces obsoletus carries a larger number of chiggers. Eumeces obsoletus is one of the principle carriers of chiggers out of all species that live Great Plains grasslands.

Economic Importance for Humans: Positive

Great Plains skinks prey on insects and arachnids that could be considered pests to humans.

• Positive Impacts
• controls pest population

Economic Importance for Humans: Negative

Great Plains skinks carry a large number of chiggers, which can be transmitted to humans.

Conservation Status

Distribution of Great Plains skinks is large but has areas of isolated colonies. These small populations are isolated because they are surrounded by inhospitable habitats with little cover and lower daily temperatures than are necessary for survival of the species.

Other Comments

Common names for Eumeces obsoletus include Great Plains skinks and Sonoran skinks.

Additional Links

Encyclopedia of Life

Contributors

Rachel Skaggs (author), Centre College, Jeffrey Mullaney (author), Centre College, Stephanie Fabritius (editor, instructor), Centre College, Tanya Dewey (editor), Animal Diversity Web.

References

Belfit, S., V. Belfit. 1985. Notes on the ecology of a population of Eumeces Obsoletus (Scincidae) in New Mexico. The Southwestern Naturalist , 30(4): 612-614.

Evans, L. 1959. A motion picture study of maternal behavior of the lizzard, Eumeces obsoletus Baird and Gerrard. The Southwestern Naturalist , 1959(2): 103-110.

Fitch, H. 1955. Habits and adaptations of the Great Plains Skink. Ecological Monographs , 25(1): 59-83.

Hall, R., H. Fitch. 1971. Further observations on the Great Plains Skink. Transactions of the Kansas Academy of Science , 74(1): 93-98.

Hall, R. 1972. Food habits of the Great Plains Skink. American Midland Naturalist , 87(2): 258-263.

Smith, H. 1946. Handbook of Lizards . Ithaca, New York: Comstock Publishing Co..

Watkins, L., L. Hinesley. 1970. Notes on the distribution and abundance of the Sonoran Skink, Eumeces obsoletus , in Western Missouri. Transactions of the Kansas Academy of Science , 73(1): 118-119.

2008. "IUCN Red List of Threatened Species" (On-line). Accessed April 03, 2009 at http://www.iucnredlist.org/details/64235 .