358 ME. B. SPEtrCE OK IKSECT-MiaEATIOKS IS SOUTH AMERICA. 



nants of the above-mentioned herbs all the year round, and doubt- 

 less also of the insects that feed upon them. There are also 

 cattle-farms ; and around the wells from which water is drawn and 

 served to the cattle, the same weeds are continually springing up ; 

 while the seeds, even of those that grew on the desert, remain im- 

 bedded in the sand and retain their vitality during all the years of 

 drought. "When the rains come on, therefore, they cause, as it 

 were, a unilateral development of the vegetation from the forest 

 across the open grounds, and a corresponding expansion of the 

 insect-life which breeds and feeds upon it. 



Results the same in principle, but diverse in mode, would take 

 place under different local cii'cumstances. Thus, if we suppose an 

 oasis in the midst of a desert exposedto the same exceptional access 

 of moisture as the desert of Chanduy with its forest skirt, there 

 would be generated an extension of organic life radiating out- 

 wards in all directions. 



Besides the migrations above recorded, I have many times in 

 South America seen butterflies flying across rivers so wide that it 

 is impossible to suppose they could be guided by any indication 

 of sight or smell. Animals of higher organization and stronger 

 reasoning- powers would probably turn aside along the shore of the 

 river or ocean in quest of food for themselves and their offspring ; 

 but there are plainly cases where frail little creatures, such as 

 butterflies, must go straight forward at a venture, and either at- 

 tain their object or perish. 



The movements of Ants registered in my journal are (as may be 

 supposed) chiefly such as were hostile to myself, and they do not 

 throw much additional light on their habits. " Ecitons," or Foraging 

 Ants (called Cazadoras in Peru), seem to be true wandering hordes, 

 without a settled habitation ; for a certain number of them may 

 always be seen carrying pupae, apparently of their own species ; 

 but they sojourn sometimes for several days whenever they come 

 upon suitable food and lodging. I have sometimes thought that the 

 name " Tauoca" or " Taboca," applied to these ants on the Amazon, 

 and also to bamboos of every kind, might indicate that they really 

 made their nest in the cavities of bamboos; but I have been 

 unable to verify it, although the name "Tachi" or "Tacyba" is 

 certainly given to certain trees {TacJiia guianensis, Aubl., Triplaris 

 surinamensis, Camb., &c.) and also to a very wicked set of ants 

 that inhabit the hollow branches of those trees. Hundreds of 

 times I have come upon marching columns of "Ecitons " in the 

 forest, and have sometimes paid dearly for my heedlessness in 



