Planet of the Bugs: Evolution and the Rise of Insects Read Free Page A

the Himalayas, while subterranean species of beetles, crickets, and cockroaches have adapted to life in caves deep underground. Some aquatic stream beetles breathe across the surface of an air bubble and can stay underwater indefinitely. Brine flies, shore flies, seaweed flies, and deer flies have developed extreme tolerance for high levels of salt and live in salt marshes and salt flats and along ocean shorelines. Springtails have evolved antifreeze compounds in their blood, and some are among the most abundant organisms on sub-Antarctic islands. At high elevations worldwide, species of icebugs, springtails, snow scorpionflies, and some flightlesstipulid flies are active on the frozen surfaces of snow fields and glacial ice. Living chironomid midge larvae have been dredged up from the depths of Lake Baikal in Russia, where they have adapted to a low-oxygen environment by evolving hemoglobin-like blood pigments. The adaptability of water boatmen bugs is remarkable: some inhabit salty water below sea level in Death Valley, California, while others live high in the Himalayan Mountains. Some swim in frigid water under ice, while others thrive in hot springs at temperatures up to 35°C. The Yellowstone hot springs alkali fly develops in the edges of scalding hot water pools with temperatures up to 50°C. Other fly larvae living in arctic ponds are known to survive winter cold temperatures as low as −30°C. One of the most impressive organisms is the South African chironomid midge fly,
Polypedilum vanderplanki
, which has adapted to extreme drought conditions by evolving cryptobiosis—a suspended-animation condition where larvae become dehydrated and tolerant to the most extreme conditions. It has been reported that these dehydrated fly larvae can tolerate immersion in boiling water as well as being dipped into liquid helium.

     
    FIGURE 1.1. Common denizens of the leaf litter, springtails (order Collembola) tolerate many environmental extremes. (Photo by Kenji Nishida.)
     
    Most insect species are not nearly so tolerant of a wide range ofextremes, and indeed, many fresh water stream insects have such a narrow range of acceptable conditions of water temperature and oxygen levels that they are very valuable to us as bioindicators of good water quality. On the other hand, hundreds of thousands of tropical plant-feeding insects have evolved physiologies that allow them to feed on and metabolize plants that are highly toxic to mammals and most other animals. Many tropical caterpillars are able to feed on toxic plants containing hundreds of chemical compounds that would kill a human. Other insects are remarkably tolerant of exposure to heavy metals, and even to poisonous chemicals specifically engineered to try to kill them. Hundreds of insect species have been reported to have evolved resistance to insecticides, and despite our best attempts to eradicate certain pest species over the past century, we have not exterminated a single one to extinction. Ironically, we can’t seem to eliminate any of the ones we would really like to be rid of, like the malaria mosquito, the human body louse, the rat flea, or the house fly, while at the same time probably millions of nontarget tropical insect species may be immediately threatened with extinction by our unfortunate habit of sheer habitat destruction.
    Perhaps it is easy to sound impressive by saying that there are more than one million insects, or anything else for that matter. Most of us don’t own a million of anything, so in practice we don’t count that high very often. But what really makes insect species diversity remarkable is not just the astronomically large number but the fact that we are talking about unique and different entities. To really grasp how extraordinary that is, one needs to begin with a clear understanding of what it means to be a species.
    “And Whatever the Man called Every Living Creature—That Was Its Name”
     
    In biology, the species is the most