June, i9i6.] WhEELER: SlaVE-RaidS OF AMAZON AnT. 113 



expeditions begin from the middle of June to the beginning of July 

 (possibly sooner in very warm localities) and end between the middle 

 of August and beginning of the September." Eniery,^ who has suc- 

 ceeded in solving the interesting problem of the establishment of ama- 

 zon colonies, gives the time of two forays of a colony in northern 

 Italy during 1908 as July 24, 4.30 P. M. and July 25, 3 P. M. and of 

 two forays of this same colony during 1907 as July 16, 4.30 to 5 P. M. 

 and July 19, as 5 to 7 P. M. 



Fore! is probably correct in supposing that the time of sortie of 

 the amazon army is determined by temperature. We may suppose that 

 a certain optimum, probably near 70° to 75° F., is required by the 

 ants. This is often attained during the sunny afternoon hours of 

 July and August in temperate North America and Eurasia. It would 

 certainly be below the usual maximum diurnal temperature and would 

 bear a certain relation to it, so that it would be reached earlier in the 

 afternoon on hot than on cool days. Thus we could account for the 

 differences in the time of sortie between the Californian amazon 

 colonies and those of the Rocky Mountains, Middle and Eastern 

 States since the average midday temperatures of July at altitudes of 

 6,000 to 8,000 ft., on the southern and eastern slopes and in the canyons 

 preferred by the ants, is certainly much lower in California than it is 

 in the other localities mentioned. It is not improbable, however, that 

 atmospheric humidity may also be a factor in determining the time of 

 sortie. At any rate, all future descriptions of amazon expeditions, 

 both in this country and abroad, should be accompanied by accurate 

 temperature, barometric and humidity records, for in time such rec- 

 ords might enable us to ascertain the precise external stimuli that call 

 forth such periodic behavior as the slave-raids and nuptial flights of 

 ants. 



2. The second matter of interest in the observations made at 

 Fallen Leaf Lake is the behavior of the males and females of brevi- 

 ceps. Emery has been puzzled by the behavior of these forms in the 

 European nifesccns. Huber and Forel had witnessed marriage 

 flights of this ant and Burrell*' described a feeble marriage flight of 



5 Osservazioni ed Esperimenti sulla Formica Amazzone. Rend. Sess. 

 R. Accad. Sci. 1st. Bologna, 1908, 16 pp.; Nuove Osservazioni ed Esperimenti 

 sulla Formica Amazzone. ibid., 1909, 8 pp.; Ulteriori Osservazioni ed Esperi- 

 enze sulla Formica Amazzone, ibid., 191 1, 18 pp. 



f> Loco citato, p. 150. 



