CLASS I. INSECTA: ORDER 4. LEPIDOPTERA. 



571 



these insects are due; and the metallic tints exhibited by many species are owing to the pres- 

 ence of very delicate stripes upon the scales. 



The larvie of the Lepidoptera are well-known as Caterpillars. These are generally more or 

 less cylindrical, composed of thirteen segments, of which the anterior forms a horny head furnished 

 with jaws and antennae, and usually with groups of simple eyes. The jaws are strong and well- 

 adapted for biting the fine vegetable tissues on which the most of them feed. 



The duration of the larva state is very variable in these insects ; many of them producing two 

 broods annually, while others occupy two or three years in arriving at their perfect condition. In 

 their larva state they are exceedingly voracious, often doing immense damage to vegetation : 

 most of them accordingly grow rapidly, and shed their skins several times before attaining maturity. 

 When this period has arrived, the caterjiillar seeks some sheltered spot in which to undergo its 

 change to the pupa form. Some species select the lower surface of leaves and branches for this 

 purpose; others, clefts and hollows in the bark of trees, walls, or palings; while others bury 

 themselves in the earth. Those which remain in the air suspend themselves in various ways by 

 means of their silky secretion, and some inclose themselves completely in a silky cocoon. This 

 is also done by some of those which conceal themselves in the earth; but many of these only line 

 their cavity with a sufficient quantity of silken threads to keep its walls from falling in upon them. 

 The pupa is entirely inclosed in a horny case, in which the position of the wings and limbs is 

 indicated, externally, only by lines and other elevations. 



In their pi'eparatory stages the Lepidoptera are exceedingly liable to be destroyed by numerous 

 species of parasitic insects, which lay their eggs in the larva; the latter still continues to feed, 

 and frequently even effects its transformation to the pupa state, without exhibiting any indica- 

 tions of the work of destruction which is going on within. These parasites, assisted by the insect- 

 ivorous birds, keep the numbers of caterpillars within moderate limits. Without these checks 

 they would soon destroy the fruit of the labors of the gardener and the husbandman.* 





THE SYBIL BUTTERFLY. 



The perfect insect, on first emerging from the pupa case, usually has the wings soft and 

 crumpled ; and it is not until some little time after it has set itself free from its prison that its 



* There are said to be twelve hundred species of lepidopterous insects in this country, and the numbers of each are 

 of course beyond computation. One female will produce three hundred eggs a year, and if her otfspring were to go 

 on at that rate of increase, in four years her progeny would be eight thousand one hundred millions. The necessity 

 of powerful checks upon such prolific and voracious species is obvious. The birds are immense destroyers of cater- 

 pillars. A single woodpecker will destroy fifty or sixty a day ; thus one million of woodpeckers, during the months 

 of April, May, June, and July, will destroy six billions annually. 



