1960] 
Creighton — Pheidolc militicida 
5 
drops rapidly towards sundown and foraging in that month ordinarily 
terminates soon after 5 :oo P. M. 'Phis brief period of foraging is 
extended as the days lengthen and by the end of February the fora- 
ging lasts about three hours. During the winter months the seeds 
of two grasses are the principal ones collected. These are the fluff 
grass, Tridens pulche/lus Hitch and the spike pappus grass, Enneci- 
pogon desvauxii Beauv. 2 Both these grasses fail to lose all their seeds 
at the end of the growing season, but the number of unshed seeds 
in the heads is low. Counts on five samples (30 cc. each) of fluff 
grass heads taken within foraging range of five militicida colonies 
gave an average of only 4.6 seeds per cubic centimeter. Nevertheless, 
these residual seeds furnish a steady, if meager, supply for, as the 
winter advances, the seeds or the spikelets containing them are gradu- 
ally blown out of the heads and deposited in a thin layer on the 
surface of the soil wherever there is a windbreak. In the winter 
months the militicida minors collect their seeds entirely from this 
layer. During the many days that the foraging minors were observed, 
not one was seen to ascend a grass stem to get at the seeds. It is 
difficult to explain this reaction, for the percentage of seeds in the 
heads is several times as great as that in the layer on the ground. 
For this layer contains many spikelets that are devoid of seeds and 
the minors frequently bring these empty envelopes home. On several 
occasions we took numbers of the spikelets away from the workers 
as they reached the vicinity of the nest and found that not more than 
a third of these contained seeds. 
Despite the short foraging period and the scant seed supply, the 
militicida minors bring in many seeds, for on warm days foraging 
is very active. Each nest entrance usually has a single foraging col- 
umn but sometimes two or three columns may leave the same entrance. 
The columns are seldom more than fifteen feet long, an indication of 
the easy availability of the seed supply, regardless of its low yield. 
Since the rate of seed consumption in the captive colonies was very 
low, it seems probable that winter foraging augments the number of 
seeds stored in the nests. The militicida colony is thus provided with 
an abundant store of seeds which it can use with the arrival of spring. 
The spring months ’are the driest part of the year in the areas where 
militicida occurs. At Portal the total precipitation during April, 
May and June averages 1.52 inches, approximately 8.2% of the an- 
2 We wish to thank Mr. Joseph Welch, who was working at the Station 
when this study was made, for his kindness in identifying these and other 
grasses as well as for helpful suggestions on the terminology of the spikelet. 
