To give a succinct overview of the complete fauna of Amazonia is as impossible as it is to adequately describe the great diversity of its flora; in part this is because many of the region’s species have yet to be identified. The rivers and streams of the basin teem with life, and the forest canopy resonates with the cries of birds and monkeys and the whine of insects. There is a notable paucity of large terrestrial mammal species; indeed, many of the mammals are arboreal.

More than 8,000 species of insects alone have been collected and classified. Myriads of mosquitoes may transmit diseases including malaria and yellow fever. Leaf-cutter ants (of the genera Atta and Acromyrmex) are prevalent, as are the ubiquitous small black flies known as piums in Brazil. Fireflies, stinging bees, hornets, wasps, beetles, cockroaches, cicadas, centipedes, scorpions, ticks, red bugs, and giant spiders are abundant. Most spectacular, however, are the hundreds of species of brilliantly coloured butterflies; sometimes thousands of butterflies gather in the afternoon on riverside sandbanks.

About 2,500 fish species have been found within the Amazon system, but many more remain unidentified. Most fish are migratory, moving in great schools at spawning time. Fish represent a critical source of protein in the often meat-poor diet of the caboclo population. (The term caboclo refers to people of mixed European and Indian ancestry in Brazil who live off the rivers and forests). Among the more important commercial species are the pirarucu (Arapaima gigas), one of the world’s largest freshwater fish, and various giant catfish. The small flesh-eating piranha generally feeds on other fish but may attack any animal or human that enters the water; its razor-sharp teeth cut out chunks of flesh, stripping a carcass of its meat in a few minutes. Some fish species have become locally threatened as the worldwide demand for frozen and dried fish has increased. Tropical fish of the Amazon are also some of the most desired for food and breeding and for use as aquarium specimens. Iquitos, Manaus, and the Colombian port of Leticia are centres of these trades.

Alligators are hunted for their skins, river turtles and their eggs are considered a delicacy, and the giant sea cow, or manatee, is sought for its flesh and for oil. All are threatened by overhunting, and the manatee has been listed as an endangered species. Aquatic animals also include river dolphins (Inia geoffrensis); the semiaquatic capybara, the largest rodent in the world (weighing up to 170 pounds [80 kg]); and the nutria, or coypu, valued especially for its pelt. Other common rodents are the paca, agouti, porcupine, and local species of squirrels, rats, and mice.

The tapir, the white-lipped peccary, and several species of deer are native to the Amazon basin and much sought for their meat. Water buffalo, introduced from Southeast Asia as work and dairy cattle, predominate in the remote, swampy parts of Marajó Island.

Especially characteristic of the Amazon forest are several species of monkeys. Of note are the howler monkeys, which make the selva resound with their morning and evening choruses. The small, agile squirrel monkey, the most ubiquitous of Amazonia’s monkeys, is used in laboratories, as is the larger spider monkey. Among a host of other primate species are woolly monkeys, capuchin monkeys, titis, sakis, and marmosets. All species are used for food and frequently are seen for sale in local markets. As the human population increases and the shotgun replaces the blowgun, hunting of the wild fauna has been mounting.

Large cats, such as the jaguar and ocelot, have become rare, though pumas may be found in larger numbers in the Andean fringe of the basin. Smaller carnivores include coati, grisons, and weasels. Countless bats inhabit the Amazonian night, including the blood-eating vampire bat.

Other animals of the forest include two varieties of arboreal sloths, three types of anteaters, armadillos, and iguanas, the last especially prized for their flesh. Among snakes the nonpoisonous boa constrictor and anaconda are notable for their size, the latter reaching lengths up to 30 feet (9 metres).

The Amazon basin is exceedingly rich in birdlife. Morning and evening, the parrots and macaws fly to and from their feeding grounds, their brilliant plumage flashing in the sunlight and their raucous voices calling out their presence. Throughout the day the caciques quarrel in trees where their hanging nests swing by the dozens. Hoatzins screech in noisy flocks from streamside brush, while solitary hawks and eagles scream from tree stumps. Everywhere is heard the twittering of small birds, the sound of woodpeckers, and the guttural noises of such waterbirds as herons, cormorants, roseate spoonbills, and scarlet ibises. Parakeets, which are more common in the Amazon than sparrows are in the United States, fly around in great flocks. At dusk, toucans cry a discordant plaint from the treetops and are joined by ground-dwelling tinamous and quail. The night air is filled with the cries of various species of nightjars.

Early settlement patterns

The Amazon basin has long been relatively uninhabited. At the time of the European conquest, the bottomlands and fringing upland surfaces of the Amazon River and its major tributaries supported relatively dense, sedentary populations of indigenous peoples who practiced intensive root-crop farming, supplemented by fishing and by hunting aquatic mammals and reptiles. The more-elevated areas away from the rivers and their floodplains were—and still are in some of the more remote sectors—inhabited by small, widely dispersed, seminomadic tribes of Indians. These groups traditionally have relied predominantly on hunting large and small animals and on gathering wild fruits, berries, and nuts while practicing small-patch agriculture of low yield. In the early 1990s the Indian population of the Amazon basin numbered about 600,000, of whom perhaps close to one-third lived in Brazil and the rest in the Oriente regions of the four Andean countries. However, by the early 21st century the Indian population had dropped to fewer than 200,000, partly as a result of deforestation and commercial exploitation on their lands.

The Amazonian Indians early devised means of making the poisonous bitter cassava (manioc) edible; the end product, called farinha, became a food staple widely used today in much of tropical America. Amazonian Indians perfected the use of quinine as a specific against malaria, extracted cocaine from the leaves of the coca tree, and collected the sap of the Brazilian rubber tree. They were skilled navigators in their dugout canoes and sailing rafts (jagandas), and they invented the blowgun and the hammock. One of their arrow poisons, curare, has been used to treat a host of paralyses and spastic disorders, including multiple sclerosis.

The early European explorers of the Amazon provisioned themselves from the food supplies of the Indians they met and commandeered their canoes. Large numbers of Indians were taken into slavery, especially during organized raids (bandeiras) from the 16th to the 18th century; many others succumbed to such European diseases as influenza, measles, and smallpox. The result was a complete breakdown of native life and a precipitous decrease in the Indian population; survivors fled into increasingly inaccessible sections of the Amazon basin. As late as 1906 there were reports of the wholesale capture of Indians who were enslaved in order to tap rubber, which was plentiful and commanded a high price on the world market but which was difficult to exploit because rubber trees were sparsely scattered over a huge area.

Settlement by Europeans and mestizos (those of mixed Indian and European ancestry) did not occur to any appreciable degree until the 1870s and ’80s, when victims of severe droughts in northeastern Brazil began to move into Amazonia to profit from the rubber boom. Another wave of immigration began at the end of World War II, spurred by the rapid economic development of the region.

Most of the surviving Indian peoples live in the remote areas of the basin. Those living north of the Amazon River speak languages of the Arawaks and Caribs, while those to the south speak predominantly Tupian languages. Tupian was used as a lingua franca between Europeans and Indians until the Portuguese became dominant in the 19th century; nonetheless, Brazilian Portuguese has been heavily influenced by Tupian. Finally, there are known to be “undiscovered” Indian groups living in the Amazon region—i.e., those located so remotely that they have yet to be encountered or who have intentionally been left alone by outsiders.