Tracking the armadillo expansion into Illinois

In the past decade, people living in southern Illinois have seen armadillos in their backyards, in the field, or, in most cases, as roadkill. Sightings of armadillos are becoming common as they continue what appears to be a northward expansion. Armadillos have become established in the region, and some already consider them a nuisance. Monitoring species movement into new spaces is important because this expansion is the result of changing conditions that favor their presence, which also represents an introduction of new competition and food for the local ecosystem. 

A unique lineage of mammals in the state

The Mexican nine-banded armadillo (Dasypus mexicanus) is an extraordinary mammal. The armadillo is related to anteaters, extinct glyptodons, and sloths, and all of these animals share a common origin and center of diversity in South America. 

Armadillos possess small bones known as osteoderms in their skin, and their shell is made of bones and sits over vertebrae partially fused to the pelvis – this is why they walk “funny.” They have a distinctive long nose, and their olfaction is extraordinarily well-developed, enabling them to detect insects and other prey underground. Their teeth arrangement and cheek muscles are weak, which limits the types of food they can consume. Although considered omnivorous, they mainly prey on insects, forage on eggs, or on small vertebrates. Armadillos are riparian, meaning they thrive in sites near creeks and streams. They are primarily nocturnal yet have shown crepuscular, dawn and dusk, or even diurnal, daytime, behaviors during winter. 

Aramadillos - An animal on the move

Armadillos were documented in the northern banks of the Rio Grande in the southwestern U.S. in 1849, and since then, their range has expanded by approximately 1,700 kilometers. They have now become established in most of the southeastern states. This is possible because armadillos thrive in habitats that offer access to insects and their larvae, as well as relatively high humidity. Areas like these include modified environments, and in Illinois, it has been shown that they thrive on edges, including the edges of forests or roads. Although commonly seen in agricultural fields, these are not ideal habitats for the armadillos. In great part, their rapid expansion is the result of landscape fragmentation and climate change.

Illinois neonatives

Because the armadillo dispersed by its own means into Illinois, the animal is now considered a native mammal. A neonative species is a plant or animal that is from one region, but has migrated to a new area because changing weather patterns or human interference made it difficult to thrive in their original region. This shift in species is likely going to become more common as the climate changes. Read more about this in What to expect with invasives and climate change. 

Changes in the environmental conditions and their biological features help explain their dispersion into the Midwest. First, fragmented landscapes create the “edge habitat,” which holds a greater diversity of insects and other animals that can sustain the armadillos. Temperature patterns have shifted toward shorter winters and warmer mean temperatures during this cold season, which decreases winter mortality. From one fertilized egg, armadillos give birth to identical quadruplets, and pups are common in the early spring. 

These three points together increase the chance of armadillo survival from one year to the next. Furthermore, scientists hypothesize that the animals have become adapted to the weather in lower Midwest.

The role of armadillos as sinks of infectious diseases

Across their range, armadillos are exposed to a variety of infectious agents. In most cases, armadillos act as a “sink” for these pathogens, or they typically don’t spread most pathogens they are exposed to. However, in cases where animals are common near human encroachments, they become instrumental for the continuation of the life cycle of pathogens. 

In the Americas, armadillos are notorious because, aside from humans, they are the only known mammal capable of carrying the pathogen that causes Hansen’s disease or leprosy. As such, armadillos have become a valuable resource for studying the replication of the bacteria and are useful in designing drugs that prevent their replication. However, the transmission of this pathogen is still unknown, and there is a risk that a continuously growing population of these animals may facilitate the establishment of the pathogen in the region. Thus, surveillance of these organisms is recommended, as the results of some surveys have helped localize the pathogen in the northern parts of Mississippi and the western part of Kentucky. 

Learn more about the armadillo: 

• Outdoor Illinois Journal: Understanding the nine-banded armadillo in Illinois
• Wildlife Illinois: nine-banded armadillo
• Outdoor Illinois Journal: Research on the nine-banded armadillo

This blog article was written by Agustin Jimenez, Associate Professor of Zoology at Southern Illinois University Carbondale. 

About Everyday Environment

Everyday Environment is a series of blogs, podcasts, webinars, and videos exploring the intricate web of connections that tie us to the natural world. Want to listen to us chat about this topic? Check out the podcast episode on this topic to hear more from the Everyday Environment team about wildlife resources.

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