INSECTA 



125 



the activity, food, enemies, dispersal, migration, mentality, or 

 other phenomena connected with animal life. 



Geologic Distribution. — Insects of some kind have existed 

 for a long time geologically, insect remains being found in the 

 lower and upper Silurian. 



Economic Importance. — Insects devour our crops, carry dis- 

 ease, annoy us when awake and prey upon us when we sleep, 

 injure or destroy our stock, infest our orchards, and in some 

 countries the white ants do much damage to dwellings. The 

 damage to our American crops has been estimated at the enor- 

 mous sum of $700,000,000 in one year. But when we remember 

 that insects are also dangerous 

 to health and life, how much 

 more is the number of injuri- 

 ous insects to be deprecated. 

 Kellogg says, ' ' Mosquitos help 

 to propagate and are almost 

 certainly the exclusive dis- 

 seminating agents of malaria, 

 yellow fever," and other dis- 

 eases; " house-flies aid in 

 spreading typhoid fever and 

 other diseases; fleas are agents 

 in distributing the germs of 

 the bubonic plague." Howard 

 says the germs of the disease 

 known as " pink-eye " are car- 

 ried by very minute flies of the genus Hippelates. 

 are known to spread other diseases (Fig. 96). 



However, some insects are valuable to man. The honey-bee 

 makes honey; other insects furnish galls for ink; others, dye- 

 stuffs, such as cochineal; while others serve as scavengers, 

 and the silkworm (Fig. 97) furnishes our finest clothes. The 

 bumble-bee fertilizes the clover blossoms, other insects cross- 

 fertilize the flowers of many plants, and many serve as food for 

 birds. Thus, while some insects are very harmful to us, others 

 are very valuable to us. If we (with the help of the birds) 

 exterminate those which are injurious and protect those which 



Fig. 96. — Tsetse fly, which causes 

 a disease of cattle in Africa, en- 

 larged. (L. O. Howard.) 



Other insects 



