Many people are disappointed when they visit a rainforest. Few see big animals. Mostly what they see is a lot of foliage way up in the air and ants and other insects on the ground. If they are lucky they catch glimpses of monkeys and tropical birds like macaws, parrots, toucans or hornbills among the leaves and shadows.
Most rainforest animals are small (the vast majority are insects) and live high in trees, where you can't see them. Don’t expect to see lions which are depicted in some cartoons and Hollywood movies as living in the rainforest because they don't actually live there. When there are large animals in the rainforest, they, like snakes, are shy and sense you before you see them, and usually hide or keep their distance from humans.
In the rainforest there are day creatures and night creatures. At dawn and dusk the rainforest is very quiet as both the night and day insects are at rest. But this also often the best time to view animals.
Large animals in the tropical rainforest browse on the limited amount of leaves in the understory and the rich vegetation close to riverbanks.
See Separate Articles on Insects, Snakes, Etc. Under Creatures of the World
Complexity of Rainforest Creatures
It is also amazing how rainforest plants and animals are continually adapting to their environment. Plants develop poisonous alkaloids to protect them against insects; insects develop digestive chemistry to overcome these poisons; and aboriginals use the alkaloids these plants as well lethal frogs to tip the blowgun darts and spears.∩
Many species are confined to small areas or niches. The have specialized ecological needs and are easily affected by habitat change. Some flowers can only be fertilized one bee or bat and if they are lost the flower is also lost.
At night the tropical rainforest is alive with a variety sounds: howls, screams, clicks, whirs, coughs, barks, trills. Scientist have a great difficulty determining what kind of creatures make these sounds. Many of the sounds are territory claims where visual cues can not be seen and laying sent markers is too cumbersome.
Dramas are constantly taking place in the rainforest on a miniature scale. Thorn-shaped treehoppers are protected from spiders and wasps by ants who feast on the treehopper's sugar laced excrement; flies mating in mid air are gobbled up by giant butterflies and moths; arboreal dragonflies fly across the leafy crowns of trees the same way they skim across ponds; polychromatic frogs and lizards are swallowed whole by snakes; and ants with bear trap jaws rotate their head vertically to snag insects.▸
Camouflage and Deception among Rainforest Animals
Camouflage and deception are important for the survival of many species in the rainforest and the tropics where there is a lot of animal life and nearly everything is food for something else. Among the creatures that excel at the art of deception are leaf-litter toads, that disappear into the forest floor in Panama; the flag-footed bug, which attempts to divert a hunter’s attention with red flags on the insect’s legs that keep hunters away from essential organs on its main body; and caterpillars that rear up like striking snakes when threatened and display a par of spots that look like scary snake eyes. Walking leafs from Malaysia can be as long as 10 centimeters. They are little changed from ancestors found in 47-million -year-old fossils in Germany. [Source: Natalie Angier, National Geographic, August 2009]
Describing the creatures on Barro Colorado Island in Panama, Natalie Angier wrote in National Geographic, “Parts of the tree seem to be unfixing themselves and wandering at will. A four-inch twig buzzes overheard and thuds into a nearby branch. A lime green leaf stares through a pile of brown leaves, finds nothing of interest, and crawls towards another pile. The “twig” is a stick insect, a magnificent specimens of the Plasmatodea clan, its outer sheath persuasive rendering of striated bark, its tubular body and head punctuated by fake axillary buds and leaf scars---the little knobs and notches that make a twig look twiggy...During the day these insects move little and are nearly impossible to distinguish from the sylvan backdrop they imitate, and that, of course, is the point: to remain invisible to sharp-eyed predators that use vision to hunt. Come nightfall, however, stick and leaf katydids shake off their vegetable torpor to some feeding of their own---on leaves and forest-floor detritus. [Ibid]
In many cases---perhaps most cases---camouflage and deception allow a creature to avoid predators or elude detection by prey or both. Angier wrote “I found a mantid that looked like a few sprigs of radicchio, the perfect cloaking device for a stealth hunter or a leaf-eating insect that itself is much coveted by insectivorous reptiles and birds.” Katydids often employ mimicry because they are fleshy, protein-rich and toxin free and as a result are frequently fed on by monkeys, birds, lizards, frogs and snakes. The same is true with nonpoisonous butterflies that have developed markings similar to those of poisonous species. [Ibid]
Visual mimicry is the most well-documented and obvious form of mimicry but auditory mimicry also exists. One species of tiger moth that bats like to feed on, for example, produces ultrasonic clicks of moths that bats detest. The great racket-tailed drongo of Sri Lanka mimics she calls of other birds to generate mixed-species flocks in which drongos can more safely and efficiently forage. In New York, small green frogs sometimes croak like large green frogs to keep intruders away from their territory. [Ibid]
There is also olfactory mimicry. Some species of orchids produce smells like dead meat to attract flies that serve as pollinators. Bolas spiders attract male moths by producing imitations of the female moth’s scent. There is even tactile mimicry. One species of parasitic fungus makes its home in termite nest by adopting the shape and texture of eggs of essentially blind termites. [Ibid]
Scientists are particularly interested in mimicry that seems incomplete or imperfect in some way to gain understanding into different means of deception are created and what happens when they outlived its usefulness and the creature is evolving away from it. Evidence shows that wingless stick insects have evolved wings and got ride of at least four times in their history. This finding shocked scientists. [Ibid]
Rainforest Mammals and Birds
About 70 percent of the 4,000 known mammal species are found in rainforests. About 90 percent of all primates are found in the tropical forests.
The most abundant mammals in the tropical rainforest are mice and rats. The two note mating whistles of some species of rat are often mistaken for the calls of insects and birds. Most of the mice are nocturnal animals whose vision is enhanced by huge dilating pupils. Wooly opossums are the most abundant mammal in the canopy of undisturbed forest in the Amazon basin.
Of the 9,000 known bird species, more than half are found in rainforests, with about a fifth of them in the Amazon. There are lots of birds and bird species in the rainforest because there lots and lots of different kinds of insects, fruits, seeds, flower nectar for them to feed on Birds are important for dispersing seeds. Many birds fly through the trees. Those that fly above the canopy are vulnerable to attacks from eagles.
In the understory of the tropical rainforest, mixed-species flocks of 12 to 13 birds sometimes forage together. In the canopy a similar pattern exists with completely different species. The different species in the flocks often have the same 28 to 33 acre territories, with individual birds staying in the same territory for years.
Bats, See Creatures of the World
Rainforest Insects and Worms
In a single square mile of tropical rainforest there are 50,000 different insect species (more than all the world's mammal, bird, reptile and amphibian species combined). They include bumblebees the size of small birds, six-inch praying mantises, nine-inch walking sticks, grasshoppers, leafhoppers, dragonflies, beetles, ants, mites, bees, katydids, caterpillars, and weevils. A single site can have more species of katydids and beetles than are found in all of Europe.
Many species of insects have their unique species of mites and parasites that live on them. Most species of rainforest mites, which may be the most abundant creatures in the canopy and the most important in breaking down nutrients, have yet to cataloged are labeled. Most mite species that have been described have only been discovered in the last few years. Some insects specialists have discovered thousands of new species.
Among the most bizarre insects found in the rainforest are poisonous caterpillars that look like pieces of cotton candy; giant weevils that carry miniature gardens of lichens and mosses on their backs; and ants that groom each other while spreading antibiotic substances. Some species of grasshopper pretend they are wasps to keep predators away. Some kinds of damsel flies raid spider webs to steal the immobilized insects and pop the spiders "like a grape." Treehoppers are well-protected with hard shells and spikes on their backs. ▸
The rainforest is full of wasps. Some species build their nests from wood pulp, and if it rains they lap up water drops to keep the nest from disintegrating. Katydids sometimes gather around wasp nests as protection from predators and the wasps themselves smear a black secretion around the nest to repel ants who feed on wasp larvae.
Velvet worms found in the rainforest have some unusual mating habits. Among some species, the male deposits sperm on the top of the female’s head. The males of other species puts sperm on their heads and delivers it to the genital area of the females at the rear of their bodies. In some species females lay eggs outside their bodies; others lay them inside their bodies; others still give birth to live young.
Insects, Ants, Leeches, See Creatures of the World
Rainforest and Disease
Nathan Wolfe, a professor of epidemiology at Stanford University, found that 60 percent of pathogens he was studying in Africa had animal origins. Wolfe is studying bushmeat eaters in the forests of Cameroon to discover new diseases and contain them. “If you find diseases before they’ve really emerged,” he told the New York Times, “you can control them early on, before you get a major epidemic.”
Wolfe collects blood samples from bush meat hunters to get an idea of what animal diseases the hunters are exposed to and to get an idea of what animal viruses present the greatest threat to humans. He has come across several viruses never before seen in humans, including retroviruses in the same family as HIV. HIV and Ebola have documented primate origins.
Image Source: Mongabay mongabay.com
Text Sources: The Private Life of Plants: A Natural History of Plant Behavior by David Attenborough (Princeton University Press, 1997); National Geographic articles. Also the New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.
© 2009 Jeffrey Hays
Last updated March 2011