THE PHYLA ARTHROPODA AND ONYCHOPHORA 



for the most part by the eminent Austrian biologist Karl von Frisch and since 

 confirmed by many other experimenters. ^ 



Ants appear even more specialized in their social life than other hymenop- 

 terans, since there are no existing examples of solitary ants, and since the 

 workers of most ant colonies are specialized into two or more castes which 

 carry on special activities. Ant colonies, particularly in some of the tropical 

 species, may be very large, as judged both from the size of the nest and from 

 the number of individual members. The essential features of social organiza- 

 tion are illustrated by many of our native forms. In a typical example, the 

 males, which are winged throughout their brief existence, participate in the 

 mating flight with the females and then die. These females, the queens, then 

 pull off their wings, establish nests, lay eggs, and tend the young until workers 

 develop to carry on these labors. When the mating season approaches, 

 winged males and females are produced and leave the nests in the swarms that 

 are seen at certain seasons of the year. 



Ants, bees, and wasps among the Hymenoptera, as well as termites (order 

 Isoptera, p. 458), are of particular interest because of their social life and 

 their behavior. From the standpoint of social organization, insects represent 

 the only group in which anything approaching the complexity of human 

 society exists. From the standpoint of animal behavior, these insects exhibit 

 amazing instinctive reactions, the result of inherited reflexes so fixed in their 

 nature that they have become recognizable characteristics of the species, just 

 as reliable as any morphological characteristics. 



Order Diptera (two wings) — true flies, such as the housefly and the 

 mosquito. The mouth parts of the dipterans are typically suctorial, although 

 they have been modified in various ways, as for lapping and for piercing and 

 sucking. There is an anterior pair of membranous, functional wings; the 

 posterior wings are much reduced to form club-shaped halteres or balancers 

 (Fig. 15.37), which vibrate in flight and have been demonstrated to serve as 

 gyroscopic stabilizers. The life cycle is holometabolous, with larvae com- 

 monly known as maggots. 



The common housefly, Musca domestica, is perhaps the most familiar of all 

 insects; and, since it is recognized as a carrier of disease-producing micro- 

 organisms, its life cycle is widely known. The adult has mouth parts adapted 

 for lapping fluids; in feeding, it generally extrudes saliva onto the food and 

 then ingests the saliva with dissolved food substances. The fly feeds upon 

 almost any kind of organic matter that may be available. The extent to 

 which houseflies may become distributors of bacteria can be shown by allow- 

 ing a single individual to crawl across a sterile plate of nutrient gelatin 

 and noting the colonies of bacteria which later appear along its trail. Eggs 

 are laid in various kinds of decomposing organic matter. Larvae, or maggots, 

 hatch in about 6 hours and grow through three larval instars, lasting a total 



'For a fuller and entirely delightful account of these and other interesting phenomena 

 among honeybees, see Karl von Frisch, Bees: fheir Vision, Chemical Senses, and Language, copy- 

 right 1950 by Cornell University Press. 



475 



