Anteaters (Myrmecophagidae)

(Myrmecophagidae)

Class: Mammalia

Order: Xenarthra

Family: Myrmecophagidae

Thumbnail description
Small to large functional insectivores, characterized by a very elongated tapered and tubular snout, teeth are absent, wormlike tongue that is capable of extending beyond head length, large powerful curved claws, all but one species has grasping prehensile tail

Size
12–110 in (0.32–2.8 m); 0.5–86 lb (0.15–39 kg)

Number of genera, species
3 genera; 4 species

Habitat
Neotropical forests, savannas, and grasslands

Conservation status
Vulnerable: 1 species

Distribution
Belize, Mexico, Central and South America

Evolution and systematics

Fossil evidence indicates that the family Myrmecophagidae was present during the early Miocene period (25 million years ago [mya]) in South America. However, the fossil record is poor and it is possible that the family is much older. Myrmecophagidae is the only member of the infraorder Vermilingua, which means worm-tongue. There are three genera and four species. Anteaters were once thought to be closely related to sloths. However, analysis of albumin samples indicates that the members of the order Xenarthra diverged about 75–80 mya and are very distinct.

Physical characteristics

All members of this group have elongated snouts and a thin tongue that is capable of extending outward to a length greater than the length of the head. They have a tubular mouth with lips but they do not have teeth. They also have large curved foreclaws that are used to tear open ant and termite mounds. The powerful foreclaws can also be used as lethal weapons for defense. All but one species has a grasping prehensile tail. The fur is long and thick to protect them briefly from the attack of ants as well as termites.

Distribution

Two members of this group are found as far northward as Southeastern Mexico, the other two members begin their northernmost range in Cental America. The ranges of three members of this group overlap to eastern Brazil. Two species extend southward to Uruguay.

Habitat

Anteaters can be found in tropical dry forests, rainforests, grasslands and savannas. The silky anteater (Cyclopes didactylus) is an arboreal specialist that is most commonly found in rainforest. The tamandua are arboreal and terrestrial opportunists in regards to terrain and food resources. They are most commonly found in dry forests near streams and lakes. The giant anteater (Myrmecophaga tridactyla) is almost entirely terrestrial and usually found in grasslands and savannas.

Behavior

Anteaters are thought to be mostly solitary. The limited number of field studies done indicate that all members of this group will defend their 1–1.5 mi² (2.6–3.9 km²) territories. Males often enter the territories of associated females but do not enter the territories of other males. Likewise, females do not enter the territories of other females. If a territorial dispute occurs, they will vocalize, swat with the foreclaws and sometimes sit on and even ride the back of a subordinate animal.

Observations indicate that anteaters have a poor sense of sight, being able to see better the closer they get to the subject. However, their sense of smell is exceptional. Most species depend on smell for direction, foraging, feeding and defense. They are thought to be able to hear very well.

Anteaters are unique in the fact that they have the lowest body temperature of any mammal. Their normal body temperature is also more variable and they can safely tolerate more fluctuation in body temperature than most mammals. The body temperature of a giant anteater fluctuates between 90 and 95°F (33–36°C). There is evidence from field studies that anteaters operate at the minimal energetic requirements for a mammal feeding on insects. In other words, energy consumed from food is only slightly greater than the energy used in everyday activities. It is suspected that anteaters coordinate their body temperatures with respect to activity and energy requirements. They can conserve energy with a lower body temperature during periods of rest; conversely when increased activity levels are needed during periods of foraging or hunting for example, the body temperature increases as a result of this energy requirement.

Feeding ecology and diet

Anteaters are specialized to feed on formidable insects. Very few mammals would consider feeding on invertebrates that are capable of defending themselves with powerful jaws, a potent sting, prickly armor, and in some species the ability to shoot acids and toxins at the enemy. The feeding strategy of anteaters is to lick up as many ants and termites as possible, as quickly as possible. The insect attack quickly becomes unbearable. In fact, an anteater spends only about a minute at a typical nest before it must move on to another. These animals must feed on thousands of ants and termites each day to satisfy their caloric requirements. For example, a giant anteater may visit close to 200 ant and termite nests a day in order to get enough food. Anteaters feed on many different species of ants and termites, both terrestrial and arboreal; however, the bulk of their diet is composed of only a few species. Each anteater species has specific insect preferences, depending on the locality in which it is found. Anteaters also practice resource partitioning. The species of insects upon which they feed depends on ant and termite nest construction and the location of that nest. Some ant and termite species are arboreal and only found on small branches, making them inaccessible to large anteater species. Others have a hard covering on the nest making it impenetrable to smaller anteater species.

An anteater's tongue is darted in and out very quickly and is covered with thousands of tiny hooks known as filiform papillae. These hooks help to grasp insects. Large quantities of saliva also help to hold the insects until they reach the mouth. Slight side to side movements of the jaws aid in moving the tongue and swallowing. The stomach of an anteater is specialized to aid in digestion much like the gizzard of a bird. The stomach has hardened folds and uses strong contractions as well as small bits of ingested sand and dirt to grind the insects.

Reproductive biology

Visual sex determination of anteaters is sometimes possible. Adult males tend to be slightly larger overall and have a wider head and neck as well as a more muscular build. The penis and testes are located internally in the abdominal cavity between the rectum and urinary bladder. As a result, the only sure way to determine the sex of an anteater visually is to observe the shape and size differences of the urogenital opening. In males, the opening is more ventral and greatly reduced. Thus, the distance from the anus to the urogenital opening is greater in males. Females have a shorter ano-genital distance, the uro-genital opening is long and has a mound-like shape. This can sometimes be seen at a distance with the larger species when the tail is raised, otherwise the animal must be captured for close identification. There is no intromission during breeding, fertilization occurs as a result of contact transfer similar to that observed in some species of lizards. Usually only a single offspring is produced from polygynous mating, twins are possible but very rare. Females have a single pair of mammae near the armpits from which the offspring nurse. Mothers are unable to grasp the newborn offspring due to the enlarged foreclaws; therefore, newborn youngsters must climb up the long extended fur to the mammae. In most species, the young are transported on the mothers back until they are self-sufficient.

Conservation status

Accurate census numbers on these animals have been difficult to obtain. They are solitary, have a low reproductive rate, are difficult to find, and seem to have large home ranges; these factors make population studies very challenging. As a result, their natural history is poorly understood and their conservation status is difficult to assess. They are found in a wide range of habitats. However, much of their range is suffering from the pressures of habitat alteration, destruction and human encroachment. It has yet to be determined how well they can adjust and survive in disturbed habitat. Their survival is also linked to the availability and health of ant and termite populations. This group is in desperate need of detailed study.

Significance to humans

Members of this group are hunted for sport and for their skin. Rope is made from the tendons of the tail from the species that have prehensile tails. They are often kept as pets and used by native peoples in their homes for ant and termite control.

Species accounts

Resources

Emmons, Louise H. Neotropical Rainforest Mammals, A Field Guide. Chicago: University of Chicago Press, 1990.

Engelmann, G. F. "The Phylogeny of the Xenarthra." In The Evolution and Ecology of Armadillos, Sloths, and Vermilinguas, edited by G. Gene Montgomery. Washington, DC: Smithsonian Institution Press, 1985.

Flint, Mike. North American Regional Studbook for the Giant Anteater. Tucson: Reid Park Zoo, 2001.

Montgomery, G. G. "Cyclopes didactylus." In Costa Rican Natural History, edited by D. H. Janzen. Chicago: University of Chicago Press, 1983.

Montgomery, G. G. "Impact of Vermilinguas On Arboreal Ant Populations." In The Evolution and Ecology of Armadillos, Sloths, and Vermilinguas, edited by G. Gene Montgomery. Washington, DC: Smithsonian Institution Press, 1985.

Best, R. C., and Y. Harada. "Food Habits of the Silky Anteater (Cyclopes didactylus) in the Central Amazon." Journal of Mammalogy 66 (1985): 780–781.

[Article by: Ken B. Naugher, BS]