The nine-banded armadillo (Dasypus novemcinctus) is increasingly observed in areas far beyond its traditional range. This armored mammal, once primarily associated with the southern United States, has steadily expanded its territory northward. Scientists are investigating the environmental factors driving this spread.
Armadillo Origins and Spread
Armadillos originated in South America, with ancestors migrating into North America approximately three million years ago during the Great American Interchange. An earlier species, Dasypus bellus, ranged as far north as Missouri, Iowa, and Nebraska before becoming extinct around 11,000 years ago.
Their current northward expansion into the United States began relatively recently. They crossed the Rio Grande from Mexico into Texas around the mid-19th century, with human-facilitated releases also establishing populations in Florida. Since then, their spread has been rapid, extending into states like Louisiana, Oklahoma, Arkansas, Mississippi, Alabama, Georgia, and Florida by 1995. More recently, they have been noted in Illinois, Missouri, Kentucky, Tennessee, Indiana, and parts of Iowa, Nebraska, Ohio, and Virginia.
Impact of Changing Temperatures
A primary factor influencing the armadillo’s ability to move into cooler regions is its unique physiology. With low body fat, sparse fur, and a low basal metabolic rate, they are particularly susceptible to cold temperatures. They cannot shiver effectively, meaning prolonged freezing weather can be fatal due to hypothermia or starvation.
Milder winters, with fewer extended freezes and warmer average temperatures, directly reduce this environmental barrier. Research suggests armadillos can establish populations as long as the average minimum temperature does not consistently drop below approximately 17°F. This moderation of cold extremes allows them to persist and expand their range.
Finding New Homes and Food
Beyond temperature, suitable habitats and ample food sources facilitate the armadillo’s northern movement. These adaptable animals thrive in diverse environments, from forests and scrublands to grasslands. They prefer areas with moist, loose soil, essential for their extensive digging for shelter and food. Riparian corridors, often associated with water, are particularly favorable for dispersal.
Armadillos are primarily insectivores, with a diet mainly of insects, grubs, earthworms, and other invertebrates. Their keen sense of smell allows them to detect prey up to eight inches deep in the soil. While insects form the bulk of their diet, they are opportunistic feeders, consuming small reptiles, bird eggs, carrion, and occasionally plant matter like fruits and seeds when preferred prey is scarce. Disturbed soil, such as in agricultural or suburban areas, provides readily accessible food, supporting their establishment.
Ecological Implications of Their Arrival
The arrival of armadillos in new ecosystems has several ecological consequences. Their prolific digging habits can aerate the soil and contribute to nutrient cycling. These burrows also create microhabitats, offering shelter for other small creatures and potentially enhancing local biodiversity.
However, their digging can also disturb ground-nesting birds or damage plant root systems. As insectivores, armadillos help control insect populations and serve as prey for larger predators. A consideration is their ability to carry the bacterium Mycobacterium leprae, which causes leprosy. Transmission to humans is rare and primarily associated with direct contact, such as handling or consuming infected armadillos.