424 INTRODUCTION TO ZOOLOGY CHAP. 



large bath sponges. These are formed of earth or of a woody 



or papery substance made of particles of plant-tissue glued 



together with a secretion from the mouth. 



Other small suspended nests are made only of silk, or of 



leaves bound together with 

 silk, such as the nest of 

 the common ant in Central 

 Africa (Oecophylla smarag- 

 dina). These nests are 

 especially interesting be- 

 cause of the very strange 

 way in which they are 

 constructed. No adult in- 



FIG. 318. The Worker of an Ant (Oeco- sec t s known have the 



SpZZf;lTa g k h, g - t a sst Power of .pinning silk, 

 (After Doflein, from Wheeler.) though their larvae fre- 



quently possess it, and in 



order to make their silken nests, the adult ants exploit the 

 silk-spinning capacity of their grubs. They seize a grub, 

 and hold it out with the head forward, pressing this 

 gently against the leaf, or whatever it may be to which 

 the nest is to be attached, and then pull the larva away 

 (Fig. 318). A very fine silk thread is then drawn out 

 from its mouth, and this thread is attached again by once 

 more pressing the head of the grub against some object ; the 

 process is continued until the whole web is woven. In 

 the case of some foreign Aphid-keeping ants, their larvae are 

 actually carried some distance to the Aphid herd, and there 

 used in building a silken shed over the Aphides. 



Many ants which live above ground, instead of making 

 their own nests, take advantage of the hollow cavities 

 which occur in some plants. They take shelter in these 

 cavities, and as in some of these plants extra-floral nectaries 

 happen to be present, the ants in such cases find a ready- 

 made home with food provided. 



Leaf-cutting ^e Leaf-cutting Ants of tropical and sub- 



and Fungus- tropical America, belonging to the genus Atta, 



growing present perhaps the most marvellous development 



n s ' of any of the ant family, for they undoubtedly 



cultivate a special fungus crop for food. 1 In the first place 



1 Belt, The Naturalist in Nicaragua. 



