Look, it's another 'hillbilly speed bump,' aka an armadillo | St. Louis Public Radio


Aug 14, 2008

This article first appeared in the St. Louis Beacon: August 14, 2008 - You're driving down I-44 about an hour south of St. Louis. You glance at another dead opossum by the side of the road.

Look again. These days that possum is very likely to be an armadillo.

The armadillo population in Missouri has exploded in the past 20 or so years, to the point that the Conservation Department published an article in The Conservationist last November about living with these pesky creatures. '"Pesky" not because they are dangerous, but because in their constant quest for insects and grubs, they dig up whole lawns and golf courses. Consuming more than half a pound of insects a day, a single armadillo can do a whole lot of digging. In southern Missouri, sometimes a newly sodded lawn seems like an invitation for the armadillos to "come and get it -- the digging is easy."

Armadillos have been steadily dispersing northward since they first crossed the Rio Grande into Texas in the 1850s. Relatives of anteaters and sloths, they are native to South America, which is still the home of most species. But the armadillo we know, the nine-banded armadillo, has been able to expand its habitat as far north as the Missouri River (and perhaps beyond). It has even crossed the Mississippi into Illinois, according to Joyce Hofmann of the Illinois National History Survey. In her informal survey, she has been getting more frequent reports of armadillos in southern Illinois counties. Lots of sightings have been near Belleville.

Professor Lynn Robbins of Southwest Missouri State University saw his first armadillo in the early 1980s. When he reported it to the Conservation Department, they told him it must have been an exotic pet released. Two years later, they called back and said, "Robbins, we have a problem."

Tracking the Wild Armadillo

Robbins, a zoologist, became intrigued with the armadillo population explosion. In 1996, he published a paper looking at armadillo numbers and the expansion of their range. (Taulman, J F, and Robbins, L W 1996. Recent range expansion and distributional limits of the nine-banded armadillo (Dasypus novemcinctus) in the United States. Journal of Biogeography 23: 635-648.)

It seems that these primeval-looking creatures are radiating from two centers. When we think armadillo we usually think Texas. But in the 1930s, hurricanes destroyed some roadside zoos in Florida and the released armadillos immediately began to breed and multiply. Since the '30s, they have moved westward from Florida, eastward from Texas, and always north.

In fact, Robbins was able to predict how the armadillo dispersal would continue, based on the armadillo biology at the time.

  • They wouldn't go too far west, because deserts would be a barrier: too hot and dry, and not enough bugs.
  • They would continue to push north until the winters prove too harsh. Armadillos do not hibernate, and have very little body fat. They can't survive when the average temperature is consistently lower than 28o F for a month. (See below -- this statement has proven not entirely true.)
  • They like forested areas and tree-lined stream beds, where the bug supply is abundant.

The predictions, for the most part, have been right. The nine-banded armadillo continues to expand its range at about ten times the average rate for a mammal, according to another zoologist's website .

What accounts for armadillos coming soon to your own backyard?

This Darwinian example of an animal population naturally expanding to fill a niche can be blamed neither on global warming nor destruction of habitat.

But habitat does play a role. As settlers moved into Texas in the 1850s, they plowed up lots of the natural grasslands and created mesquite forests. The armadillos that were able to cross the Rio Grande found a happy habitat, with plenty of leaf litter, lots of bugs and grubs under the litter, and cover.

Furthermore, the new habitat was nearly predator free. Native populations in Latin America like to eat armadillo -- they say it tastes somewhat like pork -- but Texans do not. These creatures have few other natural enemies. The hard shell covering all their topside except for the ears seem to make them unattractive to mountain lions and coyotes.

(Some Americans turned to armadillo meat during the great Depression. They called it “Hoover hogs” in sarcastic reference to the promised "chicken in every pot.")

So, some growing armadillo families foraged for food and followed river and stream beds north.

What about global warming?

According to Robbins, global warming will eventually determine the limits of northern expansion, but it has not yet been a major factor. Although some armadillos will starve during a harsh spell in a Missouri winter, many find good places to hide and survive. Scott McWilliams who works the armadillo front lines as a Wildlife Damage Biologist in West Plains, Mo., says "Hard, cold winters do not take them out as we used to think. The nine-banded armadillo is an extremely adaptable creature."

They love to hide under the hay bales that farmers in southern Missouri leave in the field during the winter. The ground doesn't freeze under the bales; there are plenty of bugs and grubs, and burrows can be dug.

Armadillos seem to love to hide. According to McWilliams, this hiding proclivity probably accounts for much armadillo movement to new places. Hidden in a hay bale, an armadillo can be taken across a bridge and into a new state. Armadillos have been reported to hitch rides in boxcars. During pipeline construction, they are known to tuck into pipe sections, get loaded onto trucks, and end up in new locations when the trucks are unloaded. And if the new location provides water, trees, and intermittently mild winters, the armadillo can claim a new address.

Furthermore, armadillos can swim across streams. And if the stream is not too wide, they can walk across under the water, finding insect fare on the stream bottom. They can stay underwater 4-6 minutes.

What accounts for the growing numbers of armadillos and why do we mostly see armadillos as road kill?

Simple mathematics coupled with a good survival rate shows why the population is exploding. The key is that each fertilized armadillo egg ends up as identical quadruplets.

The armadillo reproductive cycle is adapted for maximal survival. Mating (in the missionary position) occurs in July and August, but the quadruplet embryos derived from the first two cell divisions just float around in the uterus until November. After implantation, gestation begins and lasts about 120 days. Without the delayed implantation, the babies would be born in the coldest months. But those months of free floating, without development, allows the babies to be born in mild spring weather.

According to Scott McWilliams, the little ones are pretty well armored after a few weeks. The shell, made of keratin protein like our fingernails, grows with them. In only about 3 months, a baby armadillo is 2/3 adult size and becomes fully mature in less than a year.

During the summer months, these animals are nocturnal, and they like to stay in protected areas. And, although they can actually run quickly, when startled their reflex is to jump straight up 2-3 feet--just perfect for collision with a car's grill. The automobile can now be thought of as their main predator.

Expect to welcome armadillos to your neighborhood

Like the Canada goose, the armadillo stays where it is comfortable. It is very likely that this "possum on the half shell" will be a common sight in the near future.

Jo Seltzer is  freelance writer.