Wonderfully Made … the Armadillo

People tend to regard these animals as amusing spectacles. They say these creatures have eyes like a pig, the tail of a rat, ears like a mule, and armoured scales which look something like an alligator but which are really horny shields. These are scarcely flattering terms, but one has to admit there is an element of truth to them.

It is also said that armadillos are among the most primitive and unusual mammals found in the Americas. Unusual they certainly are, but primitive they are not. Rather, they are wonderfully designed for their particular environment, and in it they do very well indeed.

Armadillos belong to a group of animals called the Edentata. This name means ‘toothless’, but it is not completely accurate. All animals in this order lack incisor and canine teeth, but they may have numerous simple molars in the backs of their jaws. This category includes three very different groups of animals: the armadillos, the ant-eaters, and the sloths. As far as teeth go, the ant-eaters have none, the sloths have up to 10, and the armadillos sport peg-like molars varying from 14 to almost 100, which is more than any other mammal. This latter condition is found in the giant armadillo and is well suited to its diet of termites. The nine-banded armadillo has 32 teeth, 16 in each jaw. The teeth are cylindrical, with open areas of sensitive tissue. These teeth grow continuously and must be worn down by chewing on firm plant material.

The edentates, including the sloths, ant-eaters and armadillos, were originally part of a larger group which included aardvarks and pangolins—all had unique extra movable parts between vertebrae in the lower back. These additional parts give extra support to the animal’s hips. Armadillos benefit from this feature by having extra flexibility while digging. They dig so expertly and so fast that they disappear into the soil faster almost than you can write a sentence about it. These extra articulations in the back-bone are called xenarthrales by biologists. The group of animals characterized by this feature is called Xenarthra.

Among fossil mammals (animals which feed mother’s milk to their off-spring), those of the Xenarthra have been found in a variety of designs. Many of these fossils occur only in South America, but others are also found further north in Central and North America. There were giant sloths, the size of elephants, and glyptodonts, with solid shells of bony armour. Today, of that much larger group, only some edentates survive and even they are fewer than formerly. This is extinction, not evolution. Of about 30 fossil forms of edentates we now see only the three living families or groups already mentioned.

The three living groups of edentates live in areas which are sub-tropical or tropical. These animals not only prefer warm conditions, they actually are extremely sensitive to cold. However, almost any area may have rare spells of cooler conditions. The edentates have a most unusual feature which enables them to survive these cooler periods. They have a sophisticated heat exchange system of counter-current exchange which enables them to keep the heat trapped in the animal’s trunk (the body, excluding head and limbs) while allowing the limbs to cool. What these animals have is networks of blood vessels called retia mirabilia, which is Latin for ‘wonderful nets’. This system is composed of blood vessels meshed together in such a way that the arteries and veins lie side by side. Blood pumping through the arteries is warm because it is leaving the trunk and moving towards the distant parts of the body. With the ‘wonderful network’ however, the heat from the arteries is passed to the adjacent veins. The blood in the veins is cool because it is returning from the extremities. Thus heat energy in the blood takes a shortcut and returns to the heart rather than being dissipated out in the limbs.

Of all the edentates, armadillos are most interesting to North Americans, particularly as these animals live in the United States. This species did not always live in the USA. As a matter of fact it was not until 1880 that some specimens crossed the Rio Grande (which means large river) from Mexico and began a very successful expansion into suitable territories in the United States.

This event illustrates a most remarkable feature of these animals. Armadillos all live on land, and with their armour they are relatively heavy. One might expect them to avoid water, but on the contrary they are not afraid of water. This is just as well, because flash floods are a common hazard in much of their habitat. When faced with a body of water, the nine-banded armadillo simply sucks in enough air to inflate its stomach and intestines. This procedure confers on the armadillo enough additional buoyancy to enable it to float. Alternatively the animal may simply cross a stream bed by walking along the bottom! This brilliantly designed animal can hold its breath for as long as six minutes.

Thus the nine-banded armadillo managed to cross the Rio Grande in 1880. The remarkable talent of sucking in air has never been explained, so say the nature books. What they mean is that evolution theory cannot explain how such a unique talent could have developed, especially in an animal that lives on land. No other land animal can do this, a fact which makes it even harder to find an evolutionary explanation. The obvious answer is that the armadillo was designed with this capacity. It is a unique animal, filling a special ecological role, and it was designed for that purpose.

Other characteristics of the armadillo are equally suited to its lifestyle in nature. The conspicuous armoured plates are something like a turtle’s shell, but much more flexible. This animal has a leathery piece protecting its shoulders and another over its rear. In between are bands flexible enough to allow the animal to bend. Even the tail is covered with bony plates. Only the underparts are unprotected and the animal can remedy that when threatened by rolling into a tight ball. However, it usually prefers to avoid danger by digging itself into the ground. When doing so in a dusty place, an armadillo simply holds its breath for extended periods, just as it does in water.

Armadillos such as the nine-banded species in the United States enjoy quite a varied diet—but about 75 per cent consists of insects. These animals are especially well designed to catch their prey. Like the ant-eater, the armadillo is well supplied with sticky saliva. Also its tongue has sticky projections along it which help it to trap insects. In addition this animal has an exceptionally keen sense of smell. The nine-banded armadillo can detect worms and insects as deep as 20 centimetres (eight inches) underground. Besides these prey, armadillos feast on carrion, small mammals, reptiles, birds, eggs and vegetable matter. They are very fond of crops, particularly peanuts, melons and tomatoes.

The nine-banded armadillo adult is about 60 centimetres (two feet) long and weighs up to seven kilograms (15 pounds). This animal is comparatively long-lived, up to 15 or more years. After a gestation period of nine months (including three months during which the fertilized egg does not divide) the female gives birth to a litter of identical quadruplets. All the young in one litter are of the same sex and come from one fertilized egg. This is another unusual feature of these animals. In other mammals such an event (multiple births from one egg) is accidental, but in the nine-banded armadillo it is normal and regular. This enables the species to populate an area in a relatively short time, especially if many of the litters are female. Moreover, today in the United States, the armadillo has few natural enemies. Predators like wolves, coyotes, bears and wildcats are so few that the main threats come from dogs, cars and human hunters.

It is small wonder that the nine-banded armadillo has expanded its range so quickly in regions of suitable climate. This animal, with its specially articulated backbone, its unusual heat exchange system, its armour, its digging talents, its abilities to walk under-water or float, its sticky tongue and sense of smell, and unusual reproductive style, is a wonderfully designed animal. We can only feel richer for having learned about such a marvelous creature.