POOD AND FORAGING EXPEDITIONS. 175 



and soldiers. The latter are very much larger than the 

 former, and act as officers while the column is on the 

 march. Mr. Bates, the well-known traveller, in de- 

 scribing a column of Driver Ants some hundred yards in 

 length, has the following remarks on the officers and 

 their duties : 



" The large-headed individuals were in proportion of 

 about five in one hundred to the small individuals, but 

 not one of them carried anything in its mandibles. They 

 were all trotting along outside the column, and distributed 

 in regular proportions throughout the whole line of army, 

 their globular white heads rendering them very con- 

 spicuous among the rest, bobbing up and down as they 

 traversed the inequalities of the road." From such a 

 column a number of branch columns are perpetually 

 thrown out for the purpose of exploring the neighbour- 

 hood of the actual line of march. 



Another species, Etiton prcedator, prefers the " flying 

 column," i.e. a mass of foragers detached from their base. 



These creatures are of inestimable service to the human 

 inhabitants of the country. Snakes, rats, mice, venomous 

 centipedes, scorpions, gigantic cockroaches, &c., swarrn 

 in tropical America, and always find their way into 

 houses, whence the inhabitants cannot expel them, but 

 the Driver Ants can and will do so, and consequently 

 the approach of a flying column is hailed with joy. 



Its coming is heralded by the appearance of certain 

 birds which feed largely on these ants, and which may 

 be seen perched on the topmost branches of the trees. 



