4-0 ELEMENTARY STUDIES IN INSECT LIFE 



disturbed, disagreeable scents. These are given off for 

 the purpose of protecting themselves by repelling inimi- 

 cal insects, and more especially other enemies, such as 

 birds. There are, however, odors given off by insects, 

 evidently intended solely for the benefit of other in- 

 sects ; that is, to render themselves by the possession 

 of this odor attractive to other insects. Many of these 

 odors are perceptible to us. Our monarch butterfly 1 

 (Fig. -iSa), emits a slightly honeyed odor; the small 

 blue butterfly, 2 common in spring, has an odor resem- 

 bling crushed violet stems. Tin- white butterfly 3 gives 

 off a faint odor of syringa blossoms. These instances 

 with many others show that many butterflies emit odors, 

 apparently in most cases agreeable to us. These odors 

 are emitted through minute canals found in very small 

 scales of the butterfly wing. These scales are called 

 scent scales. As far as our sense can perceive, some 

 insects with well-developed scent scales emit no odors. 

 It is evident, then, that the odors which they emit are 

 beyond our perception, and that to such insects we 

 must attribute an exceedingly delicate sense of smell. 

 This statement is not difficult to accept, when, as be- 

 fore noted, the males of many species are able to locate, 

 within a dwelling, entirely out of sight, females of their 

 own species. They do not so much "'walk by sight" 

 as "fly by smell." 



The Sense of Sight- -The eyes of insects are of two 

 kinds, simple and compound. Of the simple eyes there 

 are generally three, situated in a triangle on the front 

 of the head. These eyes have but a single lens, and, it is 

 supposed, they are used to observe very near objects. The 



l Anosia plcxippus. '- Cyaniris pseudargiolus. s Pieris oleracea. 



