424 



POPULATIONS 



ants (Eciton) of the New World tropics 

 explore the surface of the forest floor and 

 the lower undergrowth for insect prey. 

 Masses of marauding ants form a so-called 

 raiding fan that may measure many square 

 yards in area. Every nook and crevice is 

 investigated for insect food. The nests of 

 other ants and wasps are often robbed of 

 their larvae and pupae. The prey is killed 

 or paralyzed by the sting of the ant and is 

 then carried back slung under the body 

 between the straddUng legs to the tem- 

 porary bivouac (Figs. 152, 153). Large 

 prey is dismembered by the marauding 

 workers, although occasionally several 

 workers may straddle a long insect such as 

 a caterpillar and together carry it back to 

 the bivouac. The converging trails behind 

 tlie slowly progressing fan are composed of 

 ants moving out to the fan as well as others 

 returning, many laden with prey. If the 

 trail is a large one it may be wide enough 

 for ten or a dozen ants. If the trail is over 

 rough ground or extends up a vertical or 

 sharply sloped surface, some of the workers 

 fill in the crevices or slopes with their own 

 bodies, thus making a fairly level roadway 

 upon which the other ants run. 



The workers are polymorphic, with sev- 

 eral sizes between the smallest and the 

 largest. The largest have elongated hooked 

 mandibles and are often called soldiers 

 (Fig. 147). All sizes of workers function for 

 both food capture and transportation as 

 well as defense and the building of road- 

 ways and bivouacs with their bodies. The 

 queen and the larvae are fed directly with 

 the prey. 



The most primitive ants (Ponerinae) 

 usually have monomorphic workers without 

 subdivision of the worker functions. Poly- 

 morphic workers are probably indicative of 

 quantitative or quahtative division of 

 labor, and in the more striking polymorphic 

 forms sharp divisions of function may oc- 

 cur. 



Among the honey ants (i.e., Myrmecocij- 

 stus), the workers gather honey dew (a 

 sweet, clear excretion of the sap-sucking 

 aphids, scale insects or other Homoptera). 

 This is transported in the crop back to the 

 underground nest cavities, where it is 

 transferred to other workers known as "re- 

 pletes," that store the sugary food in their 

 greatly distended crops. The repletes are 

 morphologically identical with the other 



workers before they become passive stor- 

 age receptacles. They disgorge droplets of 

 honeydew upon soHcitation by the other 

 ants. 



Talbot (1943) made a study of popula- 

 tions of the ant, Prenolepis imparls, that 

 has repletes. The repletes made up about 

 80 per cent of the workers from the fall 

 through the spring, but fell to about 67 

 per cent in the summer, when the brood 

 was maturing and foraging had ceased. Re- 

 pletes were increased in late summer, when 

 the other workers were foraging. The func- 

 tion of the repletes in the homeostasis of 

 the food supply in the social system is 

 clear. 



The astonishing adaptations of the 

 honeybees and bumblebees for the gather- 

 ing and storage of pollen and honey pro- 

 duced from nectar are too well known to 

 demand description here. A brief account 

 of the speciaHzations of flower-visiting in- 

 sects will be found on page 715. 



The fungus-growing activities of ants 

 and termites are also discussed elsewhere 

 (pp. 713, 714). Food storage and fungus 

 growing are examples of social homeostasis 

 (pp. 672, 728) and are adaptations that 

 stabihze the food supply (pp. 246, 247). 



The obhgatory slave-maker, Polyergiis, 

 is an ant that probably evolved from facul- 

 tative slave-makers such as Formica san- 

 guinea (Talbot and Kennedy, 1940). Poly- 

 ergiis has workers that have no social func- 

 tion other than to raid neighboring col- 

 onies of certain species of Formica. One 

 or two hundred slave-makers emerge from 

 their nest and travel together in an excited 

 milUng manner reminiscent of the raiding 

 systems of army ants. The direction taken 

 by the slave raiders seems to be a straight 

 line to a nest of Formica. Here they crowd 

 around the opening of the nest and enter 

 as rapidly as possible, occasionally remov- 

 ing small pebbles that may block their 

 passage. Any Formica worker offering re- 

 sistance is immediately killed. After ten or 

 fifteen minutes underground, the Polyergus 

 workers emerge, the majority usually car- 

 rying larvae, pupae or an occasional adult 

 Formica worker. A long trail of returning 

 slave-makers laden with their captives 

 moves back to the home nest without the 

 excited gyrations of the raiding group. The 

 captives are reared by the previous slaves 

 and ultimately perform the nutritional and 



