258 CONSIDERATIONS FROM STUDY OF INSECTS 



Unfortunately, not all insect parasites do good. Animals of all 

 kinds, but especially birds, are infested with lice and fleas. The 

 ticks are well known for the harm they do, while the larvae of the 

 botflies which live in the bodies of various mammals, as the horse 

 and sheep and cattle, are insect parasites which do much harm. 



Problem XXXII. SoDir i^elations of insects to man. {.Labora- 

 tory Manual , Proh. .Y.YXII.) 

 (d) With reference fn disease, 

 (b) WitJi reference to destruction of property. 

 (o) With reference to benefit to man. 



The Relation of Insects to Mankind. — We already have seen 

 this relation is twofold, harmful or beneficial. The harmful relation 

 may affect man directly, as when human disease is carried by 

 insects, or it may be indirect, as in the case of damage to crops, 

 trees, stored food, or clothing. The first relations, naturally of 

 more importance, as malaria and typhoid fever, two extremely 

 prevalent diseases, may be largely due to insects. There are 

 probably one million cases of " chills and fever " in the Southern 

 states alone every year. Malaria and typhoid could be largely 

 eradicated if there were no mosquitoes or flies. It is therefore 

 evident that a careful study of the habits of these insects is worth 

 our while. 



The Malarial Mosquito. — Fortunately for mankind, not all 

 mosquitoes harbor the small one-celled parasite (a protozoan) 

 which causes malaria. The harmless mosquito (culex) may be 

 usually distinguished from the mosquito which carries malaria 

 {anopheles) by the position taken when at rest. (See page 197.) 

 Culex lays eggs in tiny rafts of one hundred or more eggs in any 

 standing water; thus the eggs are distinguished from the eggs of 

 anopheles, which are not in rafts. Rain barrels, gutters, or old 

 cans may breed in a short time enough mosquitoes to stock a 

 neighborhood. The larviB are known as wigglers. They breathe 

 through a tube in the posterior end of the body, and may be 

 recognized by their peculiar movement when on their way to the 

 surface to breathe. The fact that both larvse and pupiE take air 

 from the surface of the water makes it possible to kill the mosquito 



