THE ORGANIZATION OF INSECT SOCIETIES 



431 



The queen termite not only attracts con- 

 siderable special attention from the workers 

 who feed her, groom her, and remove her 

 eggs to adjoining nursery chambers, but 

 seems also to be the center of a behavior 

 gradient that results in the spherical sym- 

 metry of nest-building activity. Particularly 

 in the round arboreal nests of the genus 

 Nasutitermes, the walls of the queen cell 

 and neighboring cells are much thicker than 

 those of the peripheral cells of the nest. Not 



(1938, 1944, 1945, 1947). The army ants 

 have temporary bivouacs in sheltered niches. 

 The bodies of the Kving ants compose the 

 structure of the bivouac (Fig. 152) in which 

 live the brood and the photonegative queen. 

 Large numbers of predatory workers issue 

 forth on raiding parties, subject to certain 

 periodic stimuli. The queen of Eciton hama- 

 tum becomes physogastric and produces 

 large numbers of eggs (more than 20,000 

 within a few days) at intervals of thirty-five 



Fig. 152. iJi\uuac of army ants {Eciton haniatum) on the underside of a fallen log in 

 I'anama. The larger white-headed individuals are large workers or "soldiers." (Photograph by 

 Ralph Buchsbaum.) 



only is there an activity gradient of nest- 

 building behavior centering about the 

 queen, but the walls are chemically differ- 

 ent, with gradations in the amount of 

 organic material used in their construction 

 (Holdaway, 1933). The queen is thus a 

 social analogue to a center of physiological 

 dominance within the organism and prob- 

 ably induces activity gradients in behavior 

 through chemical stimuli that are respon- 

 sible for the spherical symmetry of these 

 termite nests. 



The intricate social-stimulative effects of 

 trophallactic agents are illustrated by the 

 organization and periodicity of army ant 

 behavior. These have been carefully studied 

 in the field and laboratory by Schneirla 



or thirty-six days. The activity of the mov- 

 ing larvae excites the workers, and this ex- 

 citement increases progressively throughout 

 the colony by means of interindividual stim- 

 ulation. Any stimulation that increases gen- 

 eral excitement augments raiding, and three 

 or more extensively developed raiding 

 systems during each day of this period in- 

 evitably lead to a bivouac change in the 

 afternoon (Fig. 153). This nomadic period 

 lasts about seventeen days. When the brood 

 has become enclosed in cocoons, the colony 

 becomes statary (minimal raiding and ab- 

 sence of bivouac change) and remains in 

 this condition for about nineteen days, dur- 

 ing which time only a single raiding system 

 is developed each day and the bivouac 



