258 THE BIOLOGY OF INSECTS 



of this " trophallaxis " among the termites, as among the 

 ants and \vasps, in promoting social life. The habit is even 

 more elaborately developed in termite than in ant and wasp 

 communities ; the termites *' may be said to be bound 

 together by a circulating medium of glandular secretions, 

 fatty exudates, and partly and wholly digested food, just as 

 the cells of the body of a higher animal are bound together 

 as a svntrophic whole by means of the circulating blood." 



Termites of different kinds show much varietv' of habit 

 in the construction of their nests. The small communities 

 of more primitive forms live in irregular galleries or tunnels 

 excavated in wood or soil. A. D. Imms (19 19), in his 

 account of the Himalayan Archotermopsis, describes the 

 tunnels made by these insects in fallen trunks and logs of 

 deodar, and comments on " the complete absence of any- 

 thing in the nature of a true nest or termitarium." Many 

 of the " white-ants " that are notorious as destroyers of 

 timber buildings or furniture, such as the American 

 Leucotermes ffaripes, inhabit cavities eaten out in dry wood. 

 The " concentrated " nests of more highly organised 

 termites, begun in the underground chamber excavated by 

 the royal pair, are developed through the excavation of 

 surrounding galleries and small chambers by the workers, 

 and completed through the up-building of a broad sloping 

 mound or a steep conspicuous " liill-nest," which may 

 attain a height of fifteen or eighteen feet in the case of several 

 tropical African species, while the nests of some Australian 

 termites, t\venty or twent}'-five feet high, have been claimed 

 as the largest of all animal dwellings, if the work of human 

 builders be left out of account. The material of the above- 

 ground structure of these hill nests, like that of the earthen 

 tunnels built by many termites over the stems and branches 

 of trees and shrubs, is soil moistened with the termites* 

 spittle, or disgorged or evacuated after being swallowed, 

 and thus brought into condition suitable for use as building 

 material. *' On drying," remarks Wheeler, '' the sub- 

 stances employed, especially the saliva-impregnated earth, 

 become almost as hard as cement." Wood also, after 



