1907.] Wheeler, The Polymorphism of Ants. 87 



The first of the following examples, which seem to indicate the occurrence 

 of instinctive prior to morphological differentiation, shows at the same time 

 how the ergatotelic type of the honey-bee arose from the gyna'cotelic type 

 of the social wasps and bumble-bees. 



1. The queens of certain species of Formica (F. rufa, exsectoides, etc.) 

 are no longer able to establish colonies without the cooperation of workers. 

 The common method of colony formation among these insects is by a 

 process of swarming like that of the honey-bee: a certain portion of the 

 colony emigrates and founds a new nest with one or more of the queens. 

 When this method is impracticable the young queen seeks the assistance 

 of an allied species of Formica (F. fusca), the workers of which are willing 

 to perform the same function as those of her own species in rearing her 

 brood. In F. rufa and e.vsectoides there is nothing in the stature or struc- 

 ture of the queen to indicate the presence of these parasitic instincts, but, in 

 many of the allied species like F. ciliata, montige7ia, microgyna, etc., the 

 colonies of which are smaller and no longer swarm, or do so only to a very 

 limited extent, the queens have become more dependent on the workers of 

 other species of Formica and have developed mimetic characters or a dwarf 

 stature to enable them to enter and exploit the colonies of alien species. 



2. In many ants the callows, or just-hatched workers, confine them- 

 selves to caring for the larvae and pupae and do not exhibit the foraging 

 instincts till a later period. But even the adult workers may perform a 

 single duty in the colony for long periods of time, if not indefinitely. Thus 

 Lubbock,^ and Viehmeyer,^ have observed in certain nests pf Formica that 

 only certain individuals forage for the community. The latter has also 

 noticed that certain other individuals, indistinguishable morphologically 

 from their sister workers, stand guai'd at the nest entrances. In other 

 genera, like Camponotus, Atta, Pheidole, etc., with species that have des- 

 mergates, the morphological differentiation between foragers and guardians 

 is still unsettled. It becomes completely established, however, in certain 

 genera and species with the suppression of the desmergates. A remark- 

 able example of division of labor without corresponding structural differ- 

 entiation is seen also in the above-mentioned CEcophylla, an ant which 

 inhabits nests of leaves sewn together with fine silk. According to the 

 observations of Dodd^ and Doflein,^ when the nests are torn apart the 

 monomorphic workers separate into two companies, one of which stations 

 itself on the outside of the nest, draws the separated leaves together and 



1 Ants, Bees, and Wasps. Revised ed.. New York, Appleton & Co., 1894, pp. 45-47. 



2 Experiment elle Unteisufluingen, etc., loc. cit., p. .3.36. 



3 Notes on tlie (iupenslaiu] Green Tree Ant {(EcophyUa smaragdina Fal).?). Victor. 

 Natural., XVIII, 1902, pp. 136-140. 



^ Beobachtungen an den Weheranieisen {GScophylla sworasyrfiHa), Biol. Cent rall)l., XXV, 

 1905, pp. 497-507, 5 ligs. 



