434 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



in spite of the fact that usually no parent is present to select the diet 

 and feed the young. In contrast the human infant must be carefully 

 nourished during his early life in order to obtain a proper skeletal 

 structure and a healthy body. 



2. Insects are the only winged invertebrates, and this fact, combined 

 with other survival characteristics, has given the insects dominance 

 of the earth which even other winged forms like the birds cannot 

 dispute. With wings, insects can quickly abandon habitats when they 

 become unsuitable. Aquatic insects have winged stages in their life 

 cycles which solve the problem of desiccation, or in many instances 

 they can develop wings in time to avoid death which might be immi- 

 nent in many habitats. Fish and other aquatic forms usually perish 

 under similar adverse circumstances. 



3. The temperature of an insect's body usually follows closely the 

 external temperature to which it is exposed. In order to adjust for 

 seasonal changes the composition of the protoplasm is such that it 

 can function as a hydrophyllic colloid, to the extent that it can absorb 

 and bind the free water of the body. Thus by a short period of con- 

 ditioning, insects in every life stage, depending upon the species, can 

 be subjected to freezing and subfreezing temperatures, and a certain 

 percentage can survive long periods of low temperature. This adap- 

 tation to a condition of hibernation is one of the most important 

 survival factors in the world of insects. This is the means by which 

 most insects are fitted into a natural world and thus solve the problems 

 of changing seasons. During the winter their bodies are quiescent 

 and the metabolic rate is extremely low. When food is not available, 

 they are able to survive without it. 



Man on the other hand, who maintains a constant body temperature, 

 must have fuel in order to retain a normal temperature during periods 

 of low climatic temperature, as well as warm clothing to protect his 

 body and a good supply of food to maintain a normal high metabolic 

 rate and a continuous supply of internal heat and energy. 



4. Metamorphosis in insects is a condition allied in a way to the 

 previous factor. Different biologic stages of activity and inactivity 

 are often selective adaptations to seasonal conditions or feeding habits. 

 The common cattle pest, the horn fly, is a good example of this. The 

 only place that the larvae are able to complete their growth is in fresh 

 cattle droppings. In hot, dry, summer weather these droppings soon 

 desiccate. If and when they do, the maggots die. The selection 

 factor here has produced a short maggot or growing stage of from 

 2 to 4 days. 



Or take the case of a specialized plant- feeding larva which attains 

 great size during its short larval period. As a young apprentice of 

 entomological research working with the United States Department 

 of Agriculture m the tobacco-growing sections of Tennessee in 1915, 



