HOUSEHOLD INSECTS 257 



from storms, from the attacks of parasites, and from the 

 chastening influence of various sprays that may be used to 

 kill them. Wherever the Goccidae or plant lice are exposed 

 to the weather, the ants build shelters for them. Another 

 and less easily explained reason for the prevalence of these 

 insect pests, where ants are present, is the fact that the 

 stimulation resulting from the attention of the ants, while 

 collecting the sweet liquids which they exude, appears to 

 have the effect of greatly encouraging their fecundity. 

 Why this should be so is not precisely understood, but 

 numberless experiments, carried out with the greatest care, 

 have shown, beyond doubt, that coccids and aphides, 

 attended by ants, multiply to a much greater extent and 

 far more rapidly than similar unattended insects, kept 

 under otherwise identical conditions. A third cause of 

 increase is the fact that the ants, not content with protect- 

 ing their charges from the attacks of parasites and 

 predatory foes, especially ladybirds, persistently drive away 

 these exceedingly beneficial insects from the neighbour- 

 hood of the coccid colonies. The last method by which 

 the ant assists in the increase of insect pests, is by actually 

 transporting them from place to place. This habit probably 

 never assumes any great economic importance, still it is 

 one that cannot be ignored. On sugar-canes especially the 

 ants have been seen carrying mealy-bugs about, though 

 they probably only pick them up when disturbed or 

 frightened. 



The Argentine ant is unable to cross water, and, as a 

 consequence, streams and ditches form the best check on 

 its nomadic habits. These waterways are often crossed by 

 bridges composed of planks which do not meet in the 

 middle (Plate XV.), and therefore afford no passage for 

 the insects. 



The future of this noxious insect is one that will be 

 eagerly watched by economic entomologists that it will 

 spread to all the semitropical regions of the earth is 



