Armadillos

(Dasypodidae)

Class: Mammalia

Order: Xenarthra

Family: Dasypodidae

Thumbnail description
Small to medium-sized omnivore or insectivore with homodont teeth and a tough carapace covering portions of the back, face, tail and legs; sparse hairs cover soft underside; elongated or shovel-shaped head has small eyes and ears and powerful legs have large claws for digging

Size
Head-to-tail length: 6–59 in (0.15–1.5 m); weight: 0.18–66 lb (0.08–30 kg)

Number of genera, species
8 genera; 20 species

Habitat
Forest (deciduous, cloud, and rain), savanna, pampas, desert, and scrub

Conservation status
Endangered: 1 species; Vulnerable: 5 species; Lower Risk/Near Threatened: 2 species; Data Deficient: 4 species

Distribution
Latin America with one species ranging into southern North America

Evolution and systematics

Fossil armadillos found in South America are considered the oldest members of this order. During the Tertiary Period, they diversified in South America when it was isolated from the north. After the land bridge formed, armadillos invaded North America but became extinct there only 10,000-15,000 years ago. These invaders included giant herbivorous armadillos (pampatheres) and those resembling armadillos living today. Also present were rhinoceros-sized glyptodonts with solidly sutured carapaces without movable banding that may have had limited locomotion. Spines or club-like structures on the end of their tails were used for deterring predators or fighting other glyptodonts. These clubs could exert a force that could have caused fractures observed on fossil carapaces. Since the mid-nineteenth century, the nine-banded armadillo (Dasypus novemcinctus) has reinvaded North America, expanding its range into the southeastern United States. Similarities observed between living armadillos and their ancestors led Charles Darwin to develop the law of the succession (i.e., the same types of organisms replace one another within the same area), an adjunct to descent with modification.

Some phylogenies based on molecular data have used armadillos to place xenarthrans as a sister taxon to ferungulates (carnivores and hoofed mammals), whereas others place them with Afrotheria (elephants, hyraxes, and aardvarks). The armadillo suborder, Cingulata, split from anteaters and sloths around the Cretaceous/Tertiary boundary. Cingulata has only one living family, Dasypodidae, which has three main clades represented by the subfamilies: Dasypodinae, the long-nosed genus that arose first, Tolypeutinae (giant, naked-tailed, and three-banded armadillos), and the closely related Euphractinae (hairy, yellow, and pichi armadillos). Phylogeny within the subfamilies remains unclear. The genus, Chlamyphorus, does not appear in the analysis because populations were rare and not sampled.

Physical characteristics

The Spanish word armadillo means "little armored one." Armadillos are quite unique in that they are the last mammals to have a shell, that is, an ossification of the corium interrupted by several folds of the skin. The surface of the skin is gray or brown, quite soft and feels like leather. Thanks to the skin folds, the animal is very agile. Surprisingly stocky and low to the ground, armadillos are medium-sized mammals with extra articulating structures in the vertebral column that presumably improve digging. Armadillos are named for the tough bony carapace that covers the pelvic and pectoral girdles as well as areas on the head, limbs, and portions of the tail. Made of ossified dermal tissue covered with a horny epidermis, the carapace, ranging in color from dark to yellow-white, provides protection from thorny vegetation, conspecifics and predators. When harassed, armadillos will tuck their eyes under the shoulder shield and coil slightly to minimize the amount of exposed flesh. Three-banded armadillos (Tolypeutes) take this to the extreme and bend completely into a ball, exposing only thick carapace. Girdle-like armor banding (3–13) separated by folds of skin provides flexibility and agility in locomotion. Black to white-colored hairs may be interspersed on the cara-pace and cover their soft underbellies.

The head varies from shovel-shaped to elongated and narrow. The ears vary in length as well and can be pointed or rounded. Powerful limbs bear formidable claws for digging burrows and gathering food. Hind limbs always have five digits while the number of forelimb digits varies (three to five) depending on the species. Naked-tailed (Cabassous) and giant armadillos (Priodontes maximus) possess an enlarged claw on the forelimb used to tear into termite and ant mounds. Wielding this large claw and rotating their carapaces back and forth enable these armadillos to escape predators by burying themselves within minutes.

Distribution

Most armadillos are restricted to South America, specifically east of the Andes to the Atlantic coast and south to the

Strait of Magellan. Exceptions include the northern naked-tailed (C. centralis) and the nine-banded armadillos that have expanded their ranges into southern Mexico and the southeastern United States, respectively.

Habitat

Armadillos are terrestrial to fossorial, exploiting habitats ranging from rainforests to desert, including deciduous and cloud forests, grasslands, llanos, savanna, and thorny scrub. In tropical rainforests armadillos are second only to sloths in mammalian biomass. Adult armadillos are prey to jaguars, pumas, jaguarundis, wild dogs, maned wolves, black bears, and alligators. Probably due to their smaller size, nine-banded armadillo juveniles have twice the mortality of adults, falling prey to these and other animals including raptors.

Burrows, built for sleeping, nesting, escaping predators, or creating an insect reservoir, are dug in well-drained soils or into ant and termite mounds. Naked-tailed armadillos dig a fresh burrow nightly while nine-banded armadillos may reuse 20 burrows per year. In some species, adults and juveniles build nests in burrows by gathering and tucking grass or dead leaves between body and forelimbs, hopping backwards to the burrow, and depositing material by kicking their back feet. Female larger hairy (Chaetophractus villosus), nine-banded and Brazilian seven-banded (D. septemcinctus) armadillos construct above ground grass shelters prior to parturition.

Behavior

Armadillos are primarily solitary though young siblings and consorting pairs forage together. Llanos long-nosed armadillos (D. sabanicola) have been seen feeding in groups in elevated areas in floodplains. Social organization for most species is unknown with the exception of nine-banded armadillos. In this species, males and females have overlapping home ranges. Females may or may not share an area with each-other depending on density. Although males do overlap in home range, breeding males may use more exclusive areas. These breeding "territories" are maintained by aggression directed at non-breeding males. Female aggression in nine-banded, yellow (Euphractus sexcinctus), and larger hairy armadillos is associated with lactation. Defense of space was also seen in northern long-nosed armadillos during the breeding season.

These animals communicate through scent and sound. Secretions from glands in the anal region, on the feet, ears, and pelvic shield function for marking of habitat, identifying individuals, and advertising sexual receptivity. Chemical composition of anal sac glands changes during estrus in nine-banded armadillos and paired females conspicuously wag their tails after male solicitation. The position of large smelly glands on the yellow armadillos pelvic shield suggests a burrow-marking function. Armadillos give off a snuffling sound while foraging and some make a growling sound or a scream when captured. Both sexes in nine-banded armadillos softly chuck during courtship. A buzzing sound may be heard between mother and young. Strangely, armadillos seem unaffected by human voice. Eyesight is so poor that they may run into objects in their path.

Activity is mostly crepuscular and/or nocturnal although yellow, three-banded, northern long-nosed, and pichi (Zaedyus pichiy) armadillos forage during the day. Many species shift activity periods seasonally, becoming more diurnal as temperatures drop. Only Andean hairy (C. nationi) and pichi armadillos hibernate. Young nine-banded armadillos have a morning and an evening peak of activity. When active, armadillos mostly forage. When disturbed, many balance on back feet and tail and sniff to monitor for predators or conspecifics. If suddenly surprised, nine-banded armadillos will leap into the air and land running, startling a predator. This escape strategy is used unsuccessfully with automobiles, resulting in road kills. Armadillos are champion sleepers, spending upwards of 16 hours snoozing per day.

Feeding ecology and diet

Armadillos are primarily insectivores, feeding on adult and larval forms of beetles, ants, and termites. Some species are myrmecophagic while others opportunistically forage on invertebrates, small vertebrates, carrion, and plant material. Some ingest fruit seasonally. Armadillos ingest large amounts of dirt for mammals. It is unknown whether dirt is required for proper digestion or trace minerals or enters the gut incidentally with food.

Armadillos root around in leaf litter and pause periodically perhaps to sense soil-dwelling prey. Once prey is detected, armadillos use their formidable claws to dig rapidly, excavating small conical pits or tearing into ant and termite mounds. Their sticky tongues effectively lap up the scurrying insects. One stomach had more than 40,000 ants present. Armadillos have a very low metabolic rate, which means that they do not waste a lot of energy producing heat. This also means that they are not good at living in cold areas, because they are not efficient at keeping warm. They do not have any fat reserves, so they must forage for food on a daily basis. A few consecutive cold days can be deadly to the animals.

Reproductive biology

Mating for most species appears to be polygynous and occurs in the summer but some species breed year round in captivity. During courtship, a male follows the female and, for nine-banded armadillos, they forage together for several days. The male checks receptivity by soliciting the female to lift her tail by lightly touching her back. Fertilization occurs but implantation of the embryo is delayed for four months in some species. Most species have a litter of one to three young per year. Unique to mammals, Dasypus females exhibit obligate polyembryony, thereby giving birth to genetically identical young (two to 12 depending on the species). Parental care is solely the job of the female. Mating systems are unknown for most species except nine-banded armadillos. Gestation is 140 days, newborn are blind and naked with soft leathery skin, that hardens into armor within a few days. The young are nursed for 2–2.5 months, and start to walk around after a week and open their eyes after 3–4 weeks.

Conservation status

Of the 20 species of armadillos, 12 are listed as Vulnerable, Endangered, Near Threatened, or Data Deficient. Exploitation for food and loss of habitat are the main reasons for decline. Many populations are fossorial and have not been studied thoroughly and so their current status is unclear. The hairy long-nosed armadillo (D. pilosus) is known only from a few skins from mountains in Peru.

Significance to humans

Armadillos are exploited throughout Latin America for food. They are considered so tasty that one Mexican society circumvented food taboos by calling them turkeys. In the

United States during the Great Depression in the thirties, armadillos were readily consumed and given the names Texas turkey and Hoover hog. Souvenir purses and baskets with tail handles are formed from hollowed-out carapaces. Stuffed specimens on tip toes still line shop shelves in Mexican border towns. Armadillos are unwanted guests in suburban settings and agricultural fields. Ranchers have also targeted armadillos for extermination because their burrows report-edly lead to broken limbs of livestock and horses. Many change their minds upon hearing that armadillos are the only known predator of fire ants in the United States. Armadillos also are used as research models in the study of leprosy and development of a vaccine, because they are the only animals that can transmit leprosy.

Species accounts

Resources

Eisenberg, John F. Mammals of the Neotropics. Vol. 1, The Northern Neotropics: Panama, Colombia, Venezuela, Guyana, Suriname, French Guiana. Chicago: The University of Chicago Press, 1989. ——. The Mammalian Radiations: An Analysis of Trends in Evolution, Adapation, and Behavior. Chicago: The University of Chicago Press, 1981.

Eisenberg, John F., and Kent H. Redford. Mammals of the Neotropics. Vol. 3, The Central Neotropics: Ecuador, Peru, Bolivia, Brazil. Chicago: The University of Chicago Press, 1999.

Emmons, Louise H. Neotropical Rainforest Mammals: A Field Guide. Chicago: The University of Chicago Press, 1990.

Montgomery, G. Gene, ed. The Evolution and Ecology of Armadillos, Sloths, and Vermilinguas. Washington: Smithsonian Institution Press, 1985.

Redford, Kent H., and John F. Eisenberg. Mammals of the Neotropics. Vol. 2, The Southern Cone: Chile Argentina, Uruguay, Paraguay. Chicago: The University of Chicago Press, 1992.

Carter, T. S., and C. D. Encarnaçao. "Characteristics and Use of Burrows by Four Species of Armadillos in Brazil." Journal of Mammalogy 64 (1983): 103–108.

Delsuc, Frederic, et al. "The Evolution of Armadillos, Anteaters, and Sloths Depicted by Nuclear and Mitochondrial Phylogenies: Implications for the Status of the Enigmatic Fossil Eurotamandua." Proceedings of the Royal Society of London, Series B 268 (2001): 1605–1615.

Greegor, D. H. "Preliminary Study of Movements and Home Range of the Armadillo, Chaetophractus vellerosus." Journal of Mammalogy 61 (1980): 334–335.

McDonough, Colleen M. "Social Organization of Nine-banded Armadillos (Dasypus novemcinctus) in a Riparian Habitat." American Midland Naturalist 144 (2000): 139–151.

Merritt, Dennis A., Jr. "The La Plata Three-banded Armadillo in Captivity." International Zoo Yearbook 16 (1976): 153–156.

Pacheco, J., and C. J. Naranjo. "Field Ecology of Dasypus sabanicola in the Flood Savanna of Venezuela." In The Armadillo as an Experimental Model in Biomedical Research. Washington: Pan American Health Organization No. 366 (1978): 13–15.

Shaller, G. B. "Mammals and Their Biomass on a Brazilian Ranch." Arquivos de Zoologia, S. Paulo 31, no. 1 (1983): 1–36.

[Article by: Colleen M. McDonough, PhD; W. J. Loughry, PhD]