Can Armadillos Roll Into a Ball? Which Species Really Can

Which armadillos can roll into a ball?

The two ball-rolling species form the genus Tolypeutes, a name based on a Greek word for rolling up.

Both are small armadillos. The head and body are about 22–27 cm (9–11 in) long and adults weigh about 1–1.6 kg (2.2–3.5 lb). Their shells are yellowish to brownish and, as the name suggests, the middle section has just three movable bands.

How a three-banded armadillo rolls up

A three-banded armadillo’s armor is looser than that of other armadillos. The shell does not fit tightly against the body, which leaves a layer of air between skin and armor and gives the animal room to fold up.

When it rolls into a ball, the armadillo tucks its legs and ears inside, brings its head down and swings its short tail forward. The bony shield on top of the head and the armored tail fit together like two pieces of a puzzle and seal the gap. The soft belly, face and limbs are completely hidden inside a hard sphere.

Three-banded armadillos sometimes do not close the ball completely at first. They wait until a predator touches them and then snap shut, which can startle the attacker and may trap a paw or snout for a moment.

Because they rely on this defense, three-banded armadillos rarely dig burrows of their own. They rest under bushes or in burrows dug by other animals, such as giant anteaters. When they walk, they trot on the tips of their front claws.

How the nine-banded armadillo defends itself

The nine-banded armadillo, the only armadillo found in the US, has a different body plan. Its shell is made of many small, tightly linked plates with nine or so narrow bands in the middle. It can bend enough to fit into a burrow, but it cannot curl into a closed ball.

Instead it uses a set of other tricks:

• Running: It dashes for thorny brush or the nearest burrow, and it is faster over short distances than its waddling walk suggests.
• Jumping: A startled armadillo can leap about 0.9–1.2 m (3–4 ft) straight up, which may surprise a predator.
• Digging in: If caught in the open, it can dig a shallow hole in seconds and press itself into it, leaving only its armored back exposed.
• Wedging: Inside a burrow, it arches its back and braces its legs against the walls, so it is very hard to pull out.

These defenses work well against many predators. Young armadillos, whose shells stay soft for weeks after birth, are much more vulnerable. Their mother usually has four identical young at a time, as explained in do armadillos always have quadruplets?

Why don’t all armadillos roll up?

Rolling into a ball is only one way to use armor. Most armadillos are strong diggers that live in burrows, so escaping underground works better for them than sitting still in a ball. A tight-fitting shell also helps them push through soil and dense, thorny vegetation.

The three-banded armadillos live in dry scrub and savanna where hard ground and open terrain make quick escape underground less practical. For them, a ball that predators cannot open is a better solution. Their looser shell also traps air that helps insulate them in hot, dry conditions.

Other animals that roll into a ball

Armadillos are not the only animals that have hit on the same idea. Several unrelated creatures roll up for protection:

• Pangolins of Africa and Asia curl into a tight ball protected by overlapping scales, as described in how do pangolins protect themselves?
• Hedgehogs pull their spiny skin around their body with a ring of muscle.
• Pill bugs (some woodlice) and pill millipedes roll into hard little balls.

This is an example of convergent evolution, where unrelated animals develop similar solutions to the same problem.

Myth: all armadillos can roll into a ball

Cartoons and children’s books often show armadillos rolling up, and many people in North America assume the local armadillo can do it too. In fact, ball-rolling is rare among armadillos. Of the roughly 20 living species, only the two three-banded armadillos can form a complete ball.

Sadly, the ball defense also has a weakness. A rolled-up armadillo stays still, so people can simply pick it up. Hunting for food, together with the loss of dry forest and scrub to farming, has caused the declines that put the Brazilian three-banded armadillo on the Vulnerable list. In 2014, it became the model for Fuleco, the official mascot of the FIFA World Cup in Brazil, which brought international attention to its plight.