254 INSECTS AND MAN 



responsible for their safety, and, at the slightest sign of 

 danger, grab them up and carry them off to some hiding- 

 place. 



Complete colonies may be formed of a queen and 

 workers only ; of queens and workers ; or of a queen (or 

 queens), males, and workers ; and, with each of these com- 

 binations, there may be associated one or more of the 

 three immature stages, corresponding to each of the three 

 adult forms, or nine immature stages in all. There is only 

 one caste of workers, and in a large colony there is con- 

 siderable division of labour, some workers being foragers, 

 some nurses, and others engineers engaged in excavation 

 or sanitary work ; but any individual can, and frequently 

 does, assume the duties of any other, when necessity 

 arises. The nests may be set up practically anywhere 

 from which light and water are excluded; a certain 

 amount of humidity is necessary to them, but light they 

 detest, and, although they will go into daylight in search 

 of food, they always build their protective "sheds" over 

 the colonies of scale insects and aphides which they 

 cultivate. 



A few facts concerning the highly developed senses of 

 these ants may prove interesting. Their sense of smell is 

 exceedingly acute, and to it they owe their success in 

 finding food. Wrapping meat in paper does not suffice to 

 keep these insects away, for they quickly work their way 

 through the folds of the paper till they reach the food 

 within ; even dainties kept in screw-stoppered bottles are 

 reached, for the workers, by following the spiral threading 

 of the screw, eventually attain the interior. Again, these 

 ants may at times be observed moving in a trail across a 

 floor or courtyard towards some favoured food, as often 

 as not the route is a circuitous one, but, whether straight 

 or roundabout, if all the ants be swept away temporarily, 

 thousands more will promptly take their place and follow 

 exactly the same trail. That this phenomenon is due to 



