Dasypus novemcinctus Linnaeus 1758
Order Cingulata : Family Dasypodidae
DESCRIPTION. About the size of a terrier dog, upperparts encased in a bony carapace with large shields on shoulders and rump and nine bands in between; front feet with four toes, middle two longest; hind foot five-toed, the middle three longest, all provided with large, strong claws; tail long, tapering, and completely covered by bony rings; color brownish, the scattered hairs yellowish white. There are 30 or 32 peg-like teeth. Averages for external measurements: total length, 760 mm; tail, 345 mm; hind foot, 85 mm. Weight of adult males, 5–8 kg; females, 4–6 kg.
DISTRIBUTION. Occurs over most of the state, except for the western Trans-Pecos.
SUBSPECIES. Dasypus n. mexicanus.
HABITS. Soil texture exerts a definite influence on the number of armadillos present in a given area. Those soils that are more easily dug, other factors being equal, will support a greater population density. In the sandy soils of Walker County, a population density of about one armadillo to 1 ha (2.5 acres) is common; in Brazos County, where the soils are more heavily impregnated with clay and become packed during the dry seasons, density averages one armadillo to 4 ha (10 acres); in the rocky terrain of the Edwards Plateau, the animals tend to concentrate in the alluvial stream bottoms and den in the cracks and crevices of the numerous limestone outcroppings in that area. In the Blackland Prairies of Texas, where the soils are heavy clays, the animals are extremely rare and restricted to the vicinity of streams where they can burrow into the banks and probe for food in the relatively soft soils near water. Perhaps the most important factor contributing to the distribution of armadillos is the hardness of the soil during the dry season because the food of the animal is obtained largely by probing for insects and other forms of animal life in the ground.
Armadillos are fond of water; where climatic conditions tend to be arid, the animals concentrate in the vicinity of streams and water holes. Tracks in the mud around small ponds give evidence that the armadillos visit them not only for purposes of drinking and feeding but also to take mud baths. Excess water, however, has a limiting effect on them because they avoid marshy areas.
Few animals of comparable size have so many dens per individual as the armadillo. The length, depth, and frequency of occurrence of their burrows depend somewhat on soil conditions. In sandy areas, the animals are extremely active diggers; in addition to numerous occupied burrows, one finds many that have been abandoned or are used only occasionally as shelters. In central Texas, the majority of their dens are along creek banks, whereas in the sandy soils of eastern Texas they are found almost everywhere. On the coastal prairies the sandy knolls are especially sought as den sites, more for protection from floods than for ease of digging. In the Edwards Plateau, natural caves, cracks, and crevices among the limestone outcroppings afford abundant shelter; excavated burrows are few in number and usually shallow.
Dens vary from 1 to 5 m (3–16 ft.) in length and from a few centimeters below the surface to a depth of 1.3 m. Averaging between 17 and 20 cm in diameter, the den is usually simple, with few turns except those caused by obstacles such as roots, rocks, and so forth. Many of the shallow burrows serve as food traps, where insects and other invertebrates take refuge and the armadillo visits on his foraging excursions. Burrows that are used for breeding purposes usually have a large nest chamber 45 cm or more in diameter and contain a rather loosely constructed nest of dried leaves, grasses, and other plant items. These materials are merely stuffed into the chamber, and the animal pushes its way in and out each time the nest is used. Usually, each occupied burrow is inhabited by only one adult armadillo.
Because of their almost complete lack of hairy covering, armadillos are easily affected by climatic conditions. In the summer season, they are more active in the cool of the evening and at night, but in midwinter their daily activities are reversed and the animals become active during the warmest part of the day, usually in mid-afternoon. They do not hibernate, nor are they equipped to wait out long periods of inclement weather. In Dickens County, one of us (RDB) observed an active armadillo that was foraging in at least 8 cm of snow; however, long periods of freezing weather may effectively eliminate armadillos from an area.
Of special interest is the behavior of this animal in the water. Its specific gravity is high, and the animal normally rides low in the water when swimming. Apparently, it tires easily when forced to swim for any distance. If the stream to be crossed is not wide, the armadillo may enter on one side, walk across the bottom, and emerge on the other side. If the expanse of water to be traversed is of considerable extent, the animals ingest air, inflate themselves, and thus increase their buoyancy. The physiological mechanism by which the armadillo can ingest air and retain it in its digestive tract to increase buoyancy is not known, but it appears to be under voluntary control.
Many legends have arisen concerning the food habits of armadillos. Among the rural folks in the South, armadillos are commonly called gravediggers and are thought to dig into human graves and dine on the contents. Also, they have quite a reputation as a depredator of quail, chicken, and turkey eggs. Observations by field-workers strongly indicate that the armadillo, which usually leaves conspicuous signs of its presence, often is accused of the destruction of quail and chicken nests when the culprit is actually some other animal. A study of their food habits by examination of over 800 stomachs revealed that no fewer than 488 different food items are eaten. Ninety-three percent (by volume) of their food is animal matter, chiefly insects and other invertebrates. Among the insects, nearly 28% were larval and adult scarab beetles, forms that are highly destructive to crops and pastures; termites and ants composed about 14%; caterpillars nearly 8%; and earthworms, millipedes, centipedes, and crayfish appeared conspicuously in their diet at times. Reptiles and amphibians constituted only a small part of their diet, usually captured during periods of cold weather. Bird eggs were found in only 5 of 281 stomachs examined, refuting the idea of predation on quail and turkey eggs.
Slightly <7% of the diet was vegetable matter, and more than two-thirds of that was material ingested with other food items and represented nothing of economic importance. Berries and fungi made up 2.1% of the entire diet. Reports indicate that at times the armadillo may feed on such fruits as tomatoes and melons, but the amount of damage done to those crops is relatively small. Carrion is readily eaten when available, and dead carcasses of animals frequently are visited not only for the carrion but also for the maggots and pupae of flies found on or near them.
Reproduction in the nine-banded armadillo is marked by two distinct and apparently unrelated phenomena: the long period of arrested development of the blastocyst prior to implantation (delayed implantation) and specific polyembryony, which results in the typical formation of identical quadruplets. In normal years, about half of the females become pregnant by the end of July, which is the beginning of the breeding season. At 5–7 days the ovum forms a blastocyst and passes into the uterus. At that point development ceases, and the vesicle remains free in the uterus. Here it is constantly bathed in fluids secreted by the glandular lining of the uterus, which supplies enough nutrition and oxygen for survival. Implantation does not occur until November, about 14 weeks after fertilization. During this process, the blastocyst divides into growth centers, each of which very shortly re-divides to produce four embryonic growth centers attached by a common placenta to the uterus. Development of each of the embryos then proceeds normally, and the four young are born approximately 4 months later in March, although some females have been noted with new litters as early as February and as late as the latter part of May. These offspring are identical in sex and genetics given that they developed from a single fertilized egg.
Young are born fully formed and with eyes open. Within a few hours they are walking, and they begin to accompany the mother on foraging expeditions within a few weeks. The nursing period is probably <2 months, but the young may remain with the mother even after weaning until they are several months old. Normally the young born in one year mature during the winter and mate for the first time in the early summer of the following year.
Delayed implantation may account, in part, for the successful invasion of the armadillo into temperate regions. Without this characteristic of the reproductive cycle, the young would be born at the beginning of winter, when their chance of survival would be greatly reduced. Apparently, the reproductive cycle is easily affected by adverse environmental conditions, particularly drought conditions, probably because of the shortage of ground insects or the difficulty of obtaining them in sandy or hard, dried soils.
Armadillos are believed to pair for each breeding season, and a male and a female may share a burrow during the season. Because of the bony carapace and ventral position of the genitalia, copulation occurs with the female lying on her back. Armadillos are frequently utilized as food in parts of Texas and Mexico. The meat is light colored and when properly cooked is considered by some the equal of pork in flavor and texture.
The common occurrence of this species in eastern Texas is a phenomenon that has developed largely since 1900. When Vernon Bailey published his Biological Survey of Texas in 1905, he mapped the distributional limits of the armadillo as between the Colorado and Guadalupe Rivers with extralimital records from Colorado, Grimes, and Houston counties. By 1914 the armadillo had crossed the Brazos River and moved to the Trinity River, and, along the coast, had already reached the Louisiana line in Orange County. The northward and eastward range expansions continued over the next 40 years, and by 1954 the armadillo was known from everywhere in eastern Texas except Red River and Lamar counties. By 1958 it was known from those two counties as well, and today is abundant everywhere in the region.
Apparently pioneering was most successful in riparian habitat, and invasion was especially rapid parallel to rivers, which served as dispersal conduits. Average invasion rates have been calculated at 4–10 km (2.5–6 mi.) per year in the absence of obvious physical or climatic barriers. Possible reasons for the armadillo's northward expansion since the nineteenth century include progressive climatic changes, encroaching human civilization, overgrazing, and decimation of large carnivores.
POPULATION STATUS. Common. The nine-banded armadillo occurs statewide except in the xeric counties of the western High Plains and Trans-Pecos regions; it is common throughout central and East Texas. However, there may be reasons for concern about its status in Texas. In 1999 the late Dr. Rollin Baker, a retired mammalogist living in Eagle Lake, undertook a survey of professional mammalogists in Texas and found that almost all agreed that armadillos were considered to be more rare than in the recent past. Baker concluded that armadillo numbers along the Texas coast were decreasing, and he suggested the decline might correlate with a dramatic upsurge in the past decade of feral pigs, which may feed on newborn armadillos. Also, it has become popular for people to make jewelry and other trinkets from armadillo shells, which has likely increased the commercial harvest of the species. Recent droughts throughout Texas have no doubt contributed to a decline in this species.
CONSERVATION STATUS. The IUCN status is listed as least concern, and the armadillo does not appear on the federal or state lists of concerned species. However, if populations continue to decline in the future, our official state small mammal may warrant conservation consideration.
REMARKS. Armadillos are known to carry leprosy, and it apparently is the same strain of the microbe (Myobacterium leprae) that infects humans. Using genomic analysis, researchers identified the same strain of leprosy in 28 of 33 wild armadillos and 25 of 39 patients who lived in states where the animals are common. According to the researchers, exposure to fresh armadillo blood or tissue raises the risk of leprosy infection.
From The Mammals of Texas, Seventh Edition by David J. Schmidly and Robert D. Bradley, copyright © 1994, 2004, 2016. Courtesy of the University of Texas Press.