532 The Animal Kingdom 



Social Insects. — Most species of insects live solitary existences, 

 coming together with other members of their species only for purposes 

 of mating or hibernation. At the other extreme are those social insects 

 which live in permanent well-organized colonies. Between these two 

 extremes are many transitional forms ; so the distinction between solitary 

 and social insects is not always clear-cut. 



The best examples of the social insects not only live together in a 

 complex organization, but also have a division of labor with special 

 forms doing special tasks. 



The termites are an excellent example of an insect with a highly 

 developed social organization. Termite colonies are found in hollowed- 

 out wood or in structures formed of masticated cellulose. At times 

 winged sexual individuals may be seen emerging from these colonies. 

 These flights soon terminate when the individuals encounter a new spot 

 suitable for establishing a fresh colony. The wings fall off, and the paired 

 males and females mate. Soon both members of each pair are busily 

 excavating a small hollow for their new nest. The female then lays the 

 eggs and feeds the young with her own secretions. Very shortly, the 

 nymphs are able to fend for themselves and feed not only themselves 

 but their parents as well. The parents then retire from all duties ex- 

 cept those of reproduction, and are called (by entomologists) the 

 royal pair. As the colony develops, only wingless individuals are 

 at first produced. These are of three types or casts : the small workers 

 which feed the young and other castes by regurgitation of the food 

 they eat, the soldier caste which has large heads and powerful mandibles 

 for protection of the colony, and finally the substitute reproductive 

 caste. These latter can become reproductive if the royal pair dies. 

 The nonreproductive castes are both males and females, but their repro- 

 ductive organs are nonfunctional. In some species of termites, there is 

 no soldier caste, but there is a special caste known as the nasutes. These 

 are able to produce a drop of liquid which may be useful for repelling 

 invaders. These members of the nasutes caste have very peculiar pointed 

 heads and are easily recognized. This head is a sort of squirt-gun 

 arrangement for extrusion of this repelling liquid. 



At times, the royal pair produces winged forms which fly out of 

 the colony to establish new nests. Fertilization of the queen by the 

 male occurs at short intervals. Six thousand to 7,000 eggs may be laid 

 in a twenty-four-hour period by the queen of a large termite colony. 

 This production rate may be maintained for many years. As the queen 



