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The Invasion of the Armadillo

The animals, typically associated with the tropics, have migrated to the Midwest

At first glimpse, the most shocking thing about an armadillo is its shell of patterned armor, reflecting sunlight and giving the prehistoric-looking creature the appearance of big, waddling football. The only mammal with a hard shell, its long tapered tail marked with rings of decreasing size and elongated snout add to its unique allure. Unique it is. The only surviving member of the order Cingulata (the five other families are extinct and known only from fossil remains), the armadillo has wandered the Americas for at least 55 million years, dating back to the late Paleocene.

"In their 55 million years, very little has changed [about armadillos' appearance]," says Lynn Robbins, a biology professor from Missouri State University. "Because they fossilize so well, you can see."

On closer inspection, there's more that's fascinating than meets the eye. What's been most intriguing in recent armadillo history is where they've been moving. Of the 20 living armadillo species, all of which live in South America, the only one that inhabits the United States is the nine-banded, named for the nine rings that circle its hard body. The animal, typically associated with the tropics or Texas, has over the last 150 years migrated from the southern United States to the Midwest. It's estimated that there are approximately 30 to 50 million armadillos in this country. How much farther north the armadillo will trek is unknown. They've made their way up to approximately the southern half of Illinois.

"Armadillos have interested me for a while because to look at them on the surface, they don't seem like they'd be a rock star of mammalian expansion, and yet most other mammal species are losing territory every year," says Joshua Nixon, a biologist at Elizabeth City State University who is an armadillo enthusiast. Although he's never studied the armadillo professionally (his own research has been on rodents and circadian rhythms), Nixon has the most comprehensive "dillo" site on the web, which he's been running for more than 10 years. "They're one of the few mammals that's actually gaining ground and expanding into areas that they don't currently live in. The nine-banded has such a huge range—you can find these animals all the way from South America up into the United States. For one single species, that's very different."

How and why this armadillo, typically the size of a very large housecat, has expanded its range so rapidly is unknown, but there are theories. Many like to cite global warming as a reason the animal with warm weather roots is finding favorable temperatures in more northern locales.

"The armadillos' expansion is unique because it's been so fast," says Robbins, who in the mid-1990s published a study on their expanding range. "Some of the estimates are [that they're moving] five to eight miles per year. The records show that you don't have them one year, and then the next year you do. Then in two or three years you're inundated with armadillos, and the people up north have them now."

This expansion isn't the first North American armadillo invasion. The history of the Dasypodidae, as it's known scientifically, began some 58 million years ago. A relative of the sloth and the anteater, the armadillo came into being in South America before the continent was connected to North America. The glyptodon and panocthus were the earliest armadillo-like animals, and with their hard armor and lack of predators, their population burgeoned. Then, roughly three million years ago, as the continents shifted, North and South America became joined by a land bridge, making way for a world of predators to invade the southern continent and for other animals to head north. Despite its armor, the armadillo can fall victim to even an average dog, which is able to bite through the shell.

"Fossils show that Dasypodidae, Pampatheriidae and Glyptodontidae wandered into North America in the course of the Great American Biotic Interchange after the emergence of the Panamanian isthmus, when many animal species from northern America migrated south, and others migrated from south to north," says Mariella Superina, DVM, of University of New Orleans, who's currently doing field research in Argentina. She's been fascinated by armadillos since first sight, encountering one in Brazil in 1992 and describing it as "odd, so different, that it woke my interest."

"Some hypothesize that large canines and felines migrated south and began to prey upon these large armadillos," Superina continues, "which in turn contributed to the extinction and the migration of Dasypus bellus out of South America towards the north."

According to fossils, the Dasypus bellus, or beautiful armadillo, was very similar to today's nine-banded, but was approximately three times the size. Ancient remains of the bony scutes that made up the armor closely resemble the scutes of the nine-banded, the only difference being size.

"Armadillos are one of the very few South American animals that were able to not only deal with the influx of big predators when North and South America connected, but actually were able to live through that and do quite well," says Nixon. "A lot of the other South American animals at the time went extinct."

The beautiful armadillo continued its migration, making its way up to the Ohio River Valley. Remains of the armadillo have been found in Illinois, Iowa, Missouri and Indiana and are between 40,000 and 11,500-years-old. The beautiful armadillo went extinct approximately 10,000 years ago likely due to an ice age. Glaciers went on to cover large portions of the Midwest.

"Before our last recorded ice age, armadillos were a part of the landscape in North America and in the Midwest," says Robbins. "They're moving back into their traditional areas. There was just a big time lapse."

As the North American armadillos vanished into extinction, the armored animals in South and Central America flourished. The Aztecs called them "azotochtli", which means "turtle rabbit", and they had their place in Mayan legend, according to which they were created by the sun god to teach two lesser gods humility. A bench the gods sat upon turned into two armadillos, which jumped and threw the gods to the ground. The creature got its modern name from the Spanish conquistadores, who called it "armadillo", meaning "little armored one". Then, in 1850, after not inhabiting North America for 10,000 years, the armadillo moved to Texas. The biggest question is why, when the habitat was already there and the glaciers had long since receded from the continent, did it take so long?

"A number of publications suggested that it was carnivores keeping their population down—mountain lions, bears, wolves—and with our settling of the West and killing off of those major predators, the armadillo didn't have a natural predator," Robbins says. "So their population built up and they moved north. Our paper that we published, based on some stuff in Mexico and Central America, projected that it is true the settlers were the predators, but the predators were probably Native Americas. Armadillos are very easy to kill. So once they didn't have the predation of the local population, and we did change Texas from being an arid grassland area to putting in agriculture and planting trees near rivers, they moved north, and they moved quickly."

In its second North American invasion, the armadillo found a very hospitable climate. Preferring warmer temperatures and soft soil for digging, the armadillo uses its long sharp claws to burrow holes and find its food of choice—grubs, ants, beetles and other insects. They'll also eat plants and carrion, typically roadkill. With a poor sense of sight, the animal relies on its ability to hear and smell to find food. The armadillo often grunts as it forages for something to eat, sticking its long snout into the ground as its rough tongue with sticky saliva laps up whatever it can grab and then munches it with peg-like teeth. Armadillos' constant search for food is the bane of many whose backyards have been torn up by digging armadillos.

"There are different theories about the reason why this species was able to reach such a large geographical distribution," says Superina. "One contributing factor might be that Dasypus novemcinctus (or nine-banded armadillo) can acclimate itself easily to changing conditions and can survive in various types of habitats. On the other, this species is not very choosy about any particular food; it devours whatever it can find. An alternative explanation might be the following: nine-banded armadillos show the phenomenon of delayed implantation and of polyembryony. In conditions of stress, the birth of the offspring can occur up to 32 months after the last mating. Now, if a pregnant animal enters a new territory, it can give birth to four offspring in the first year itself, without any male existing in that particular region. If a larger number of animals wander into new territories simultaneously, then the same ensures the fast establishment of a new population."

Being a good swimmer has also allowed the armadillo to traverse mile after mile. Although large rivers are a significant obstacle, the animal has two methods for crossing smaller bodies of water. The armadillo can either enter the water and walk across the bottom, able to hold its breath for up to six minutes, or it can ingest air, retain it in its digestive tract to make it buoyant and paddle across.

Armadillos continued their expansion across the United States throughout the 20th century. During the Great Depression they were known as Hoover hogs by poor people who had to eat them instead of the "chicken-in-every-pot" that President Herbert Hoover had promised. Their widespread population and expansion hasn't been solely due to their own wanderings. Armadillos have hitched many a ride on train cars, trucks and boats and many have been moved by people, as pranks or in an effort to make them house pets, which they are not. The first specimens of the Florida armadillo can be traced back to a pair that escaped from a zoo in 1924 and a pair that was brought to the state and released by a Navy officer from Texas.

"They established some good populations in Florida and dispersed northward and westward and met up with the ones going north and east in Texas," says Robbins.

Reports of armadillos in Illinois date back to the 1970s. Joyce Hofmann, senior research scientist, mammalogist and curator of the Illinois Natural History Survey Mammal Collection, first read about the animal showing up in the state in the '90s, but says she didn't think too much of it at the time.

"Then I saw an article that showed predicted range of species included southern Illinois, and I thought, 'Wow, they must be on their way. It would be pretty cool to observe this happening and so quickly,'" says Hofmann, who went on to get a grant from the state to survey people who'd seen armadillos. "This is really a fast moving species. Most of the reports have been since 1999. It's really been in just the last few years that people have been seeing them a lot. It's a steady stream."

Some of the reports are of live armadillos, but many are of dead ones. Its modern day predator is the car. As the Lone Star State small mammal, the armadillo is also known as a Texas speed bump. With poor vision and a tendency to be nocturnal, one of the armadillo's most unique traits is that it jumps up to three feet in the air when startled, making cars passing overhead all the more deadly.

An influx of armadillos may sound intimidating, but the animal poses virtually no threat to people, other than being pesky digging up lawns. While they've been known to carry leprosy, the cases of humans getting the disease from an armadillo are rare and seem to be the result of eating undercooked armadillo meat. "They're not used that commonly in food anymore, although I have heard that people have seen armadillos in Chinatown in San Francisco," Nixon says.

Because they have such low core body temperatures, one of the lowest among mammals, armadillos are vulnerable to the bacteria that causes leprosy. Researchers have been using them to study the disease for decades and have in turn been able to develop a leprosy vaccine. Armadillos are used for other types of medical research, and their long life expectancy, up to 20 years, and the fact that females give birth to identical quadruplets are valuable for testing.

Temperature will ultimately stop the expansion of the armadillo. They can survive where the average January temperature is more than 28 degrees. With little body fat, armadillos conserve energy through reta mirabila, a system of veins and arteries that keeps heat from going into the legs and makes them very susceptible to frostbite.

"In our research, we noted that it's not the cold weather that's going to hurt them—it's total coverage by snow and ice over their feeding grounds because they need to be able to find food with their nose," says Robbins. "They seem to be adapting to areas where snow will melt off quicker along streams and rivers or under buildings and thickets where snow doesn't cover the ground as much. They have these refuges where they hang on even when there's a foot of snow on the ground.

"About five or six years ago we had 18 inches of snow, and it stayed on the ground for about six weeks," Robbins continues. "I made a prediction to the conservation department that we were going to lose our armadillos. As soon as the snow melted I went out with my cameras, and there were still armadillos. A lot of them died. We had reports of people seeing 10 or 15 armadillos dead laying out the woods, but enough survived, and lot of them moved into towns. When I asked people to report sightings of dead armadillos, I kept getting sightings of live armadillos. So my study fizzled when I was going to report the demise of the armadillos. They are survivors, and these warmer trends of winters have not hurt them any."

Just when people say the armadillos can't go any farther north, they surprise everyone by showing up in another town, in another state. It wasn't long ago that it was said they couldn't live north of Arkansas. Today, they've made it as far north as Nebraska and are expected to eventually populate the East Coast.

"The Illinois Natural Resources Department had a publication out, and they have been tracking the spread of the armadillo through Illinois," says Nixon. "They don't expect for it to get much farther north than about the middle of the state. I've gotten emails from people saying they've seen them in central Ohio. These are uncorroborated—I don't have any photos or proof. I've also had people say that they've seen armadillos in New Jersey and even in places as strange as the mountains in Oregon. If you look at the range map [of where they could possibly live], if they could get there, they could live in some of those places. They could live north of Vancouver if they could get in that area."

"I would hypothesize that it's true [that warmer temperatures are affecting their movement], but we can't use them as an indicator of global warming because we don't know how far they would have gone before it started," says Robbins. "They're still moving north in many areas, not because it's warming, but because they haven't gotten there."

Jim Hansen, director of the NASA Goddard Institute for Space Studies and an expert on global warming, includes the armadillo in a slide presentation on the changing climate. In "The Threat to the Planet," an article on global warming published in The New York Review of Books last summer, Hansen writes, "Armadillos appear to be pretty tough. Their mobility suggests that they have a good chance to keep up with the movement of their climate zone, and to be one of the surviving species. Of course, as they reach the city limits of St. Louis and Chicago, they may not be welcome. And their ingenuity may be taxed as they seek ways to ford rivers and multiple-lane highways."

Hofmann continues to gather reports of sightings in Illinois. "I have a couple records of reports from Chicago, but you know they didn't get there on their own," she says. "Things would have to get a lot warmer before they move to Chicago, but anything can happen."

Published: January 28, 2007
Issue: Winter 2007


armadillo in nj
I just seen an amadillo in my neighbors yard, so I started researching to see if it was in fact what I seen and according to this article and other online research it may be true. We live on a barrier island, our small town of west wildwood is surrounded by water and marsh land. With recent heavy rain the ants and insects are all over, plus this summer is one of the hottest on record. All of the above lead me to believe it was in fact an armadillo.
John, west wildwood nj, Aug-21-2010