INSECTS 137 



workers, both of which are potentially female animals. Such dif- 

 ferentiation existing between the different members of the same 

 species constitutes a type of polymorphism. This phenomenon is 

 shown to the greatest degree in certain species of the Ants, in 

 which the polymorphism, just as in the Bee, is exhibited for the 

 most part by the female individuals. Thus there are commonly 

 found in an Ant colony the sexually mature queen and a series of 

 sexually immature female animals, such as the large and small 

 workers, soldiers, and various intermediate forms. The structure 

 of these forms has become variously modified so that they are 

 better adapted for their particular functions. For example, the 

 mandibles of the soldiers are large and powerful. 



Many other species of Insects are found associated with Ants 

 in their nests as guests, parasites, etc. An interesting example of 

 this condition is figured in the Frontispiece. In this case, a worker 

 Ant (Lasius), having returned to the nest from a successful forag- 

 ing expedition, is shown in the process of feeding another worker 

 a drop of the collected nectar by regurgitation. A tolerated guest, 

 the primitive Insect, Ateleura, is near at hand waiting for a chance 

 to secure the food for itself. 



B. Economic Importance of the Insects 



It would be hard to overemphasize the economic importance of 

 this amazing group of animals. Thus it has been estimated that 

 the annual losses in the United States alone, due to the destruc- 

 tion of plant and animal products on the farms by various species 

 of Insects, amount to more than three-quarters of a billion dollars. 



It is usually during the larval or nymph stage of Insects that 

 damage is done to vegetation. In general the eggs of an Insect 

 are laid upon the material best suited for the larvae to feed upon. 

 In many cases as, for example, in the Moths, the eggs are attached 

 to the leaves of plants, and when the larvae hatch, they immedi- 

 ately begin to destroy the leaves. If they are present in sufficient 

 numbers, as frequently happens, the tree will be stripped of its 

 foliage and in many cases actually killed. (W. f. 262.) 



The estimate of Insect depredations given above does not 

 include the incalculable losses sustained by the human race as the 

 result of insect-borne diseases. The germs of such diseases are 

 sometimes carried externally, attached to various parts of the body 

 as, for example, in the case of the common House-fly which may 



