90 TEOPICAL NATURE, AND OTHER ESSAYS. 



wliich are eaten by the ants ; and this supply of food 

 permanently attaches them to the plant. Mr. Belt 

 believes, after much careful observation, that these ants 

 protect the plant they live on from leaf- eating insects, 

 especially from the destructive Saiiba ants, — that they 

 are in fact a standing army kept for the protection of 

 the plant ! This view is supported by the fact that 

 other plants — Passion-flowers, for example — have honey- 

 secreting glands on the young leaves and on the sepals 

 of the flower-buds which constantly attract a small 

 blacli ant. If this view is correct, we see that the need 

 of escaping from the destructive attacks of the leaf- 

 cutting ants has led to strange modifications in many 

 plants. Those in which the foliage was especially 

 attractive to these enemies were soon weeded out unless 

 variations occurred which tended to preserve them. 

 Hence the curious phenomenon of insects specially 

 attracted to certain plants to protect them from other 

 insects ; and the existence of the destructive leaf-cutting 

 ant in America will thus explain why these specially 

 modified plants are so much more abundant there than 

 in the Old World, where no ants with equally destructive 

 habits appear to exist. 



Wasps and Bees. — These insects are excessively 

 numerous in the tropics, and, from their large size, their 

 brilliant colours, and their great activity, they are sure 

 to attract attention. Handsomest of all, perhaps, are 

 the Scoliadse, whose large and rather broad hairy bodies, 

 often two inches long, are richly banded with yellow or 

 orange. The Pompilidse comprise an immense number 

 of large and handsome insects, with rich blue-black bodies 

 and wings and exceedingly long legs. They may often 



