226 HORTICULTURE FOR SCHOOLS 



There are no essential differences in the case of the fly except 

 that the forms vary somewhat and are given other names. 

 The larval form, which in the butterfly is known as the cater- 

 pillar, in the fly is called the maggot. This maggot forms a 

 cocoon as in the case of the butterfly and the adult insect 

 emerges from it. In the case of the grasshopper, the cater- 

 pillar and chrysalis stages are replaced by a form known as 

 the nymph which undergoes a series of molts, changing form 

 slightly in each molt. The young of the grasshopper is quite 

 strikingly different from the mature form, especially as re- 

 gards relative sizes of head and body. This form gradually 

 changes from molt to molt until in the final molt the adult 

 insect appears. 



337. Reasons for metamorphosis. The purpose of this 

 wonderful series of transformations is, in a word, to tide the 

 insect over unfavorable food and weather conditions and is, 

 therefore, a means whereby the survival of the species is 

 accomplished. For example, in the winter when food and 

 weather conditions are unfavorable, many insects are quies- 

 cent in the egg, and others in the pupal form. In the spring 

 when weather and food supply become improved, the quies- 

 cent forms give place to the more active stages of larva and 

 adult. 



338. Mouth-parts. Insect life is characterized by some 

 very complex variations as regards mouth-parts. In some 

 insects the mouth is adapted to a biting process, and these 

 secure their food by eating the leaves and tender parts of the 

 plants, often entirely destroying the tissue. In other insects, 

 on the contrary, as in the butterfly, the mouth-parts are long 

 tubes specialized for sucking. Such insects have no facilities 

 for breaking or tearing the tissue of the plant, and so Secure 

 their food by drawing it up through this tube. Some of 

 them, like the butterflies, suck the nectar from flowers; others, 

 such as the aphis and scale insects, pierce the tissue of the 

 plant and extract the juices from it. 



