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The following is an excerpt from a handout prepared
for Entomology 111: Insects and Human Affairs at the
University of California/Davis.
hive harvest on
A number of science fiction films, especially those made in the 50's, utilized the concept of giant insects to inspire cinematic thrills and chills. "Them" (which featured giant ants), "Tarantula" (giant spider), "Mothra" (giant moth-- whew! so scary) and a host of other films involved monstrous, mutant, radioactive arthropods. Such invertebrate colossi would be hard pressed (literally!) to survive, let alone terrorize anyone: huge blow- up versions of standard arthropods would be crushed under their own weight and it is, in fact, the chitinous exoskeleton and tracheal respiratory system that limit the size of terrestrial arthropods. The most massive living insect is the Goliath beetle of Africa ( Goliathus cacius ) measuring up to six inches long and weighing in at a whopping 3.4 oz. or only about half the mass of a cup of water. Other large insects include Titanus gigantus of the Amazon region (up to five inches long) and the weta of New Zealand, Deinacrida heteracantha (a cricket-like insect about four inches long, tipping the scales at 2.5 oz.). Megaphasma dentricus , a walking stick which reaches a length of seven inches (making it the longest insect in the United States) is dwarfed by its tropical relatives nearly twice as long. The largest insect of all times was probably Meganeura a dragonfly-like insect of the Carboniferous age (about 320 million years ago). With a thirty-inch wingspan this buzzing behemoth was only about the same size as the colorful chinese kites that depict dragonflies and butterflies. Nonetheless, this is a far cry from the car-crunching mutants of the movies.Many large insects have apodemes , intrusions of the cuticle which anchor muscles and help keep the exoskeleton from caving in. However, as they lack sufficient internal strutting, insects are limited in their ability to support the relatively great weight of their chitinous armor. In addition, the tracheal breathing passages of insects are only efficient at exchanging gasses to tissues up to 1mm away so big insects have to carry around a lot of empty space (extensive breathing passages) that can contribute to the problem of implosion.
It has been proposed (and refuted) that the oxygen content of the atmosphere has decreased since the ancient past-- prohibiting the monstrous sizes once attained by creatures at least superficially similar to those alive today. Ancient insects could, perhaps, get away with being bigger because the alleged higher vapor pressure of oxygen, way back when, permitted the gas to more easily diffuse into the insects tissue. Alternatively, the reason there are no extant insects as large as Meganeura may be that, as they basked in the sun each morning waiting for their flight muscles to reach temperatures permitting flight to commence, they would make easy prey for warm blooded predators such as birds and mammals. Of course, all these physical and chemical properties are limitations of normal chitin-- no one has ever gotten close enough, long enough to "Them" to see what's different about that giant, mutant radioactive chitin...
Copyright © 2007 Conrad Bérubé, site design, concept and scripting. All rights reserved worldwide.