INSECT 



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INSECT 



.NSECT, one of the numberless little 

 creatures which constitute, in many different 

 kinds, more than half the animal kingdom. 

 Insects include butterflies, bees, grasshoppers 

 ,and ants, mosquitoes and flies, beetles, and 

 scores of thousands of other varieties. Though 

 we usually think of them as our enemies, in- 

 sects are in many ways very useful to man, 

 and it is said that without them the earth 

 would soon become uninhabitable. If we did 

 not have the bees and other insects which carry 

 the pollen of flowers we should have almost 

 no fruit. Some of our most beautiful flowers 

 depend on insects which carry the pollen from 

 one blossom to the blossom of another, so 

 that good seed may set. Some insects also act 

 as scavengers, because they feed on dead and 

 decaying animal and vegetable matter. Honey, 

 silk and beeswax are made by insects, and also 

 a less-known but valuable product called lac, 

 from which lacquer and shellac are derived. 

 But the greatest good done by insects is ef- 

 fected by those parasitic kinds that keep the 

 destructive kinds in check. 



The destruction caused by insects will lessen 

 as our knowledge of them increases. The 

 leading governments employ trained men 

 called entomologists, whose business it is to 

 learn how to check insect pests, and to teach 

 their discoveries to farmers and fruit growers. 

 It has been found that many of the most 

 destructive insects are those that have been 

 accidentally brought in from a foreign country 

 without the introduction of parasites which 

 prevent their increase, so entomologists are 

 now trying to find and import these parasites. 

 For example, by importing a beetle from Aus- 

 tralia entomologists checked a scale insect 

 which was attacking orange and lemon trees 

 in California. 



Social Insects. What appears to be a high 

 degree of intelligence, though most scientists 

 say it is merely instinct, is displayed by the 

 social insects, those which live together in com- 

 munities (see INSTINCT) . Of these, the ant, the 

 bumblebee and honeybee, and the social 



wasps are the most commonly observed; their 

 remarkable life is described under their respec- 

 tive headings elsewhere in these volumes. The 

 ambrosia beetles have galleries beneath the 

 bark of trees, and cultivate the fungus upon 

 which they live as a man cultivates a garden. 

 Caterpillars often feed together in great num- 

 bers. In crossing what to them is desert, a 

 gravel path, they travel in caravans, the head 

 of each close to the tail of the one just ahead. 



The Developing Insect. A striking fact 

 about insects is that many of them when 

 hatched bear no resemblance to the mature, 

 fully-developed specimen, called the imago 

 (image). The butterfly, which lives first as a 

 caterpillar,, or larva, then as a chrysalis, or 

 pupa, within a cocoon, before appearing as its 

 beautiful winged self, is a familiar example. 

 The maggots which become flies, and the grubs 

 which develop into beetles and other insects 

 are also larvae, corresponding to the caterpil- 

 lar. Their second form, in which they quietly 

 remain while developing into the imago, is 

 called the pupa. This development through 

 very different preliminary stages is called 

 metamorphosis, a word which means transfor- 

 mation. Some insects have only partial meta- 

 morphosis, others none. The young locust, 

 for instance, is distinguished only by lack of 

 the wings which it later acquires. 



Definition. The name insect is given by 

 many people to almost any small crawling 

 creature. In science it refers only to one class, 

 the members of which are most easily distin- 

 guished by their three pairs of legs. Thus a 

 spider is not an insect, for it has four pairs 

 of legs; nor, of course, is a centipede. Insects 

 are also distinct in having the rings composing 

 their bodies grouped in three parts, the head, 

 thorax, and abdomen, and in breathing by 

 means of air-tubes branching through their 

 whole body. Wings are characteristic except in 

 some degenerate forms. 



Structure. The insect does not breathe 

 through its mouth. Its extensive system of 

 air-tubes derives air from nine or ten pairs of 



