Nine-banded armadillo (Dasypus novemcinctus)
AMANDA J. SMITH
Department of Wildlife and Fisheries, Mississippi State University, Mississippi State, Mississippi, 39762 USA
The nine-banded armadillo (Dasypus novemcinctus; Linnaeus, 1758) is an edentate frequently called the common long-nosed armadillo and is the only species of the order Cingulata in North America. The nine-banded armadillo is a medium sized, armored, insectivorous mammal. The bony, scaled shell of the armadillo protects it from attacks by predators. It is 1 of 7 species in the genus Dasypus. Native to South America, it now ranges into much of the southeast United States.
The armadillo prefers areas with soft soils, which allow it to dig burrows and hunt for insects with ease. It is not of conservation concern and is expanding its geographic range into the interior of the United States.
Dasypus novemcinctus has a small head with an elongated snout that is pink and pig-like, small eyes, and large, closely set ears that are 40-50% of total head length (Fig. 1). The top of the head, sides, back, and long tail are covered with ossified dermal plates, which are covered by a thick, leathery skin. The carapace is grayish-brown with many yellowish-tan scales, while the head is covered with small gray dermal scales. The carapace weighs about 16% of the total body weight (McBee and Baker 1982). This dorsal covering is divided into 3 sections: a scapular shield across the shoulders, a pelvic shield covering the hip region, and a series of 8 to 11 transverse, telescoping bands between the two shields (Hall 1981). Each band is connected to adjacent bands by a fold of hairless skin. Male armadillos tend to be larger than females; females weigh 3.6 to 6.0 kg and males weigh 5.5 to 7.7 kg (McBee and Baker 1982). Ranges for standard external measurements (lengths in mm) of males and females, respectively, are: total length, 778.0 and 752.0; length of tail, 328.8 and 340.9; length of body, 452.4 and 432.5; length of hind foot, 68.4 and 65.3 (Layne 2003).
Dasypus novemcinctus has a greater distribution than any other edentate. The southern limit of distribution extends to northwestern Argentina and Uruguay, then northward through Central America and Mexico (McBee and Baker 1982). The species occurs throughout the southeastern United States from western Texas to eastern Florida. The nine-banded armadillo is found throughout Mississippi (Layne 2003).
Form—The dental formula is i 0/0, c 0/0, p-m 7/7, total 28; the teeth are simple, peg-like, and single-rooted, and the mandible is long and slim (Fig. 2). The xenarthrous vertebrae reflect an adaptation for digging. The second and third cervical vertebrae are combined to form a mesocervical bone, and the anterior caudal vertebrae are included into the sturdy sacrum (Layne 2003). The ribs are specialized to provide additional stability, and the muscle system is greatly developed in the limbs (Jenkins 1970). A unique salivary bladder is contained within a mass of skeletal muscle. It stores a large amount of sticky saliva, suggested for foraging efficiency (McBee and Baker 1982). The female reproductive tract is archaic and highly specialized, with two kidney-shaped ovaries and a complex, primate-like uterus (Newfang 1947). Male testes descend only into the inguinal canal; there is no scrotum. The nine-banded armadillo possesses a pair of anal glands that produce a strong musty scent (McBee and Baker 1982).
Function—Dasypus novemcinctus has a low basal metabolic rate, relatively low body temperature, and high thermal conductance (Layne 2003). The armadillo can acquire a high oxygen debt, which may be related to their fossorial foraging habits of digging with their snouts under the soil for extended periods of time (Layne 2003).
Ontogeny—Dasypus novemcinctus exhibits monozygotic polyembryony in which a single fertilized egg gives rise to four separate embryos at the blastula stage following division of the inner cell mass (Loughry et al. 1998). There is little to no variation among the 4 offspring (Bagatto et al. 2000). Armadillos give birth to precocial young, who have an approximate mass of 85 to 113.5 g, and are born with open eyes and a thin, flexible carapace (Layne 2003). Developmental events occur at different times for male and female litters. Males perform acts of drinking water, consuming solid food, and weaning earlier than female litters (McDonough et al. 1998). The young begin to leave the burrow with the mother at around 2 to 3 months of age and become self-sufficient within 3 to 4 months (Layne 2003).
Reproduction—Sexual maturity for Dasypus novemcinctus is reached at about one year of age, and ovulation occurs from June to August. Embryonic diapause lasts 3 to 4 months with parturition between February and July. In Mississippi, parturition peaks in May (Layne 2003). Females have one pair of pectoral teats and one pair at the inguinal region; lactation occurs for 3 to 4 months (Layne 2003).
Population characteristics—Densities for
Space use— Dasypus novemcinctus usually inhabit self-constructed burrows with enlarged nest chambers filled with vegetative debris (McBee and Baker 1982). Armadillos share their burrow systems with many other species (cottontail rabbits, cotton rats, opossums, and skunks). Home ranges range from 2 to 20 ha, with overlap between the sexes and adult females, but little overlap between adult males (Loughry and McDonough 1998).
Diet—Insects are the primary prey of Dasypus novemcinctus; however, they are opportunistic and will also feed on small amphibians and reptiles, bird and reptile eggs, fungi, and berries (Layne 2003). The armadillo relies on olfactory cues when foraging, roots with its nose and digs into the ground with its forefeet when a food item is found (McBee and Baker 1982).
Diseases and parasites—Known parasites of Dasypus novemcinctus in North America include viruses, protozoans, helminthes, fungi, and arthropods. Compared to other mammals of the same size, armadillos have a relatively small amount of parasites (Layne 2003). Except for humans, armadillos are the only other species that acquire leprosy (Myobacterium leprae) infection. Leprosy in armadillos is usually fatal, and the symptoms occur more rapidly than in humans. There is no known evidence of leprosy transmission from armadillos to humans (Layne 2003).
Grouping behavior—Armadillos are solitary animals with social interactions restricted to mother and young and breeding periods. Play has been observed among juveniles (Layne 2003), and the juveniles are thought to discriminate between siblings and non-siblings (Loughry et al. 1998).
Reproductive behavior—Nine-banded armadillos pair for each breeding season and may also share a burrow. Because of the location of the carapace and ventral position of the genitalia, copulation occurs with the female lying on her back (McBee and Baker 1982). Adult males and females in Mississippi pair in all months except March and April (Layne 2003).
Miscellaneous behavior—Nine-banded armadillos have several responses to threat, depending on the magnitude of the stimulus. When slightly alarmed, they may remain still momentarily and then return to their normal behaviors, or they may try to hide in vegetation that is close to the ground. A distressed individual may run into its burrow, and if the armadillo is greatly alarmed, it may leap vertically into the air (Layne 2003). Another unusual behavior is their ability to walk across the bottoms of shallow and narrow waters. When swimming at the surface of the water, buoyancy may be improved by ingesting air into the stomach and intestines (Layne 2003).
Bagatto, B., Crossley II, D. A., and Burggren, W. W. 2000. Physiological variability in neonatal armadillo quadruplets: within- and between- litter differences. Journal of Experimental Biology 203:1733–1740.
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Contributing editor of this account was Clinton Smith.