6/17/13 - lethal insects of the amazon

In today's selection -- unlike in Africa, where the primary danger for early explorers had come from lions and other large mammals, the primary dangers of the Amazon rain forests were from insects. Insect life there is so vast, powerful and diverse that a single tree can serve as home to forty different species of ants, hives can number as many as a million members, and some beetles are so strong that it requires two men to pry them off a human limb:

"To witness the devastating ... danger [of the Amazon forests, explorers] needed to look no further than the insects that filled the air around their faces, and swarmed over every tree, vine, and leaf they touched. [Legendary Brazilian explorer Colonel Candido] Rondon, who had for decades watched his men be tortured, infected, and driven to the brink of madness by the jungle's multitude of insect pests, knew better than most what power such small creatures could wield. [He] regarded the threat that even jaguars posed as 'utterly trivial compared to the real dangers of the wilderness -- the torment and menace of attacks by the swarming insects, by mosquitoes and the even more intolerable tiny gnats, by the ticks, and by the vicious poisonous ants which occasionally cause villages and even whole districts to be deserted by human beings. These insects, and the fevers they cause, and dysentery and starvation and wearing hardship and accidents in rapids are what the pioneer explorers have to fear.'

"So important and ubiquitous are insects in the ecology of the Amazon that, notwithstanding their generally small size, ants alone make up more than 10 percent of the biomass of all the animals in the rain forest. From tiny parasitic red mites to cyanide-squirting millipedes to giant six-inch beetles with legs so powerful that they require two men to pry them off if they grip a human arm, the insects of the rain forest have achieved an unparalleled degree of specialization, seeking out every possible source of sustenance and advantage. They accomplish this through adaptations that extend far beyond mere physical attributes and individual behavior, and reach into the realm of complex social relationships that involve not only other members of their own species but sophisticated alliances with other forms of life as well.

"Like that of other rain forest organisms, the physical form of insects has evolved to accomplish a spectacular range of survival-related feats, from living upside down on canopy leaves to flying almost invisibly on transparent wings to biting with pincerlike mandibles so large that they are sometimes used by Indians to suture wounds. The Brazilian wasp Mischocyttarus drewensi secretes a chemical repellent from its abdomen that, when slathered onto the stem that holds its nest, forces marauding ants to turn back and abandon their plans of attack. Ants of the neotropical genus Basiceros have made themselves all but invisible on the forest floor both by camouflaging their bodies in fine particles of soil that collect in two layers of hair and by learning the value of slothlike immobility. When foraging, the ants move extremely slowly, and if disturbed, they stand perfectly still for minutes at a time, disappearing into the rotting litter around them.

"More than any other rain forest creatures, insects have extended and refined their individual capabilities through elaborate social structures. As [explorers] discovered from their first moments on the [Amazon tributary called the] River of Doubt, the powerful influence of ants, termites, wasps, and other highly regimented insects comes not only from the particular traits of any single individual, but from the collective, coordinated activities of colonies and hives that can number as many as a million members. Acting in concert, but with highly specialized roles, columns of hundreds of thousands of army ants can fan out in raiding parties fifty feet across at their front lines, harvesting huge numbers of tarantulas, roaches, beetles, scorpions, snakes, lizards, birds, and nearly anything else in their path before returning at dusk with the bodies of their prey to their common bivouac.

"Insects have also developed highly refined, mutually beneficial relationships with other rain forest organisms. Many tropical trees and plants have special sheltering cavities or nectar-producing structures for the benefit of ants, which in return then patrol them vigilantly, defending them against herbivores, tending their leaves, and eating the eggs and larvae of other potentially damaging insects. As a result of such relationships, virtually every growing thing teems with insects; a single tree in the Amazon can serve as home to more than forty different species of ant, rendering even the most casual contact with it a nightmare of painful bites."


Candice Millard


River of Doubt


Anchor Books a division of Random House


Copyright 2005 by Candice Millard


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