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Why do armadillos have shells? Why are sloths slow?

An armadillo blends in to the leaf litter on the forest floor.
Melody Bodette
Vermont Public
An armadillo looks for insects in the leaf litter at Fort Worth Nature Center & Refuge.

Why do armadillos have shells? How do they roll into balls? Why are sloths so slow? Can sloths actually move fast? How do they defend against predators? Why do they have such long nails? We learn about two unique looking animals in this episode: sloths and armadillos. These mammals are part of an ancient superorder called Xenarthra and share a common ancestor. To get answers to kid questions about armadillos we took a field trip to Texas to talk with Michael Perez at the Forth Worth Nature Center and Refuge. And to learn about sloths, we interviewed Sam Trull of the Sloth Institute in Costa Rica.

Download our learning guides: PDF | Google Slide | Transcript

  • Sloths and armadillos are part of a superorder of mammals called Xenarthra. Anteaters are also in this group.
  • Both sloths and armadillos started out in South America and moved into North America when the creation of the Isthmus of Panama connected the two land masses. These days, no sloths still live in North America, but there used to be giant ground sloths that weighed over 500 pounds and stretched out 9 or 10 feet. 
  • Sloths are slow for two reasons. First, they conserve energy by moving slowly. They mostly eat leaves and don’t take in a lot of calories. Second, when they are slow they make themselves nearly invisible to predators in the rainforest.
  • Two-fingered and three-fingered sloths share a lot of the same characteristics and they are an example of convergent evolution. They evolved similarly because they have a shared habitat, not because of a common ancestor.
  • Sloths don’t always move slowly. They can quickly swat or bite a predator if attacked.
  • Their long fingernails help them climb, and they also use those nails to defend themselves.
  • While sloths have some defenses against natural predators, they are threatened by human activity, like forest fragmentation, electrical wires and domestic dogs.
  • Most armadillos are contained to Central and South America, but one species, the nine-banded armadillo has migrated as far north as the Southern United States.
  • Armadillos have a shell to protect themselves against predators. It’s made of bone and keratin. The shell is divided into different sections.
  • Nine-banded armadillos are almost always born as quadruplets, in groups of four. Their shell starts soft but hardens up as they age. They can’t completely curl into a ball (only the southern three-banded armadillo can do that), but they are flexible like most mammals and can curl up a bit to protect their undersides.
  • Nine-banded armadillos can jump 3-4 feet in the air when they are startled! This is a great defense mechanism, but it also is a danger because they are often killed by cars, jumping up just as the car is going over them.
Jane Lindholm is the host, executive producer and creator of But Why: A Podcast For Curious Kids. In addition to her work on our international kids show, she produces special projects for Vermont Public. Until March 2021, she was host and editor of the award-winning Vermont Public program Vermont Edition.
Melody is the Contributing Editor for But Why: A Podcast For Curious Kids and the co-author of two But Why books with Jane Lindholm.

But Why is a project of Vermont Public.

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