UTILITY OF I1IHDS IN NATUBK. 



15 



pui)al form. This stage it passes without food and while 

 fixed to some object. The piq^a? or nymphs of some other 

 insects, however, move about freely, as is the case with 

 locusts, grasshoppers, and like insects ( Orthoptera) . ^ 



The pupa finally throws 

 off its outer shell, a n <1 

 emerges a fully developed 

 or perfect insect or imago 

 with wings ; although some 

 insects which, like some 

 birds, have lost the use 

 of their wings, ne^er fiy.^ 

 After the union of the sexes 

 the female insect eventually 

 deposits the eggs for the 



Pig. 8. — Piipa^ or <-lirysali(h 



next generation. Thus we have four forms which insects 

 assume : (1) the egg, (2) the larva, (3) the pupa or nvmph, 

 (4) the imago or })erfect winged insect. 



Practically all living animals of appreciable size, as well 

 as most plants that are visible to the unaided eye, furnish 

 food for certain insects. Other insects feed on dead animals, 

 dead trees, or other decaying animal or vegetal)le matter. 

 A certain larva has been known even to tunnel into marble. 

 Those insects which feed on live vesfetation or livin"' animals 

 are capal)le of doing great harm if they increase unduh' ; 

 while those that feed only on dead animals or dead and 

 deca^'ing vegetation can do onl}^ good in nature, although 

 they may be injurious to man by destroying hides, furs, pre- 

 served meats, or clothing. 



It is difficult to perceive the usefulness of those so-called 

 injurious species which feed on the different })arts of plants ; 

 still, the larva' that eat the buds, the caterpillars that feed 



' In the Orthoptera the transformations are imperfect; the larva; of grass- 

 hoijpers, for example, are provided with well-developed legs, and much resemble 

 the imago or perfect insect, hut are without wings. In this stage they are usually 

 called nymphs. As they approach maturity they enter what is virtually an im- 

 perfect pupal stage, hut retain their shape, limbs, and activity. Tliey now show 

 rudimentary wings, hut it is only at maturity that they are capaltle of flight. 



- The Thysanura, or lowest order of in.sects, including " bristle tails," " spring 

 tails." " fish moths," and the like, never become wmged or develop any trace of 



