1981] 
Droual & Topoff— Genus Pheidole 
139 
rainfall on July 9 only three emigrations occurred, but within 9 days 
after this rainfall 29 emigrations occurred. During this 9 day period 
13 of the 15 colonies being observed on this site emigrated at least 
once. 
The emigration distance for both species was variable. Mean 
emigration distance for P. hvatti was 1.8 ± 1.0 m (N=137; range 0.3 
— 4.9) and mean emigration distance for P. desertorum was 2.5 ± 
1.4 m (N=102; range 0.4 — 6.9). The larger emigration distance of 
P. desertorum over that of P. hyatti correlates with the larger size of 
this species (mean length of P. hyatti minor = 2.64 ± 0.04 mm, 
N=50; mean length of P. desertorum minor = 3.14 ± 0.03 mm, 
N=57). 
Despite the high emigration frequency of both species, colonies of 
neither species tended to move far from the nests at which they were 
first discovered. Tables 1 and 2 show the number of times each 
colony returned to a former nest, and the distance between the first 
and last nests. As can be seen, 49% of P. desertorum ’s emigrations, 
and 42% of P. hyatti" s emigrations were to former nest sites, and 1 1 
P. desertorum colonies and 5 P. hyatti colonies at the end of the 
study were at the nest at which they were first discovered. This 
crisscrossing pattern of emigrations is illustrated for three colonies 
of each species in Figs. 6 and 7. The relative location of the nests 
reveal a clumped rather than a linear arrangement which would be 
expected if the colony were emigrating out of an area. The dates of 
nest movements for each colony show that the variability of 
emigration interval within each colony was considerable. This can 
be readily seen by examining the ranges of emigration intervals for 
the colonies shown in Figs. 6 and 7: for the P. hyatti colonies the 
ranges are, H-Jnl4-2: 1-17 days; H-Jnl4-3: 3-18 days; H-Jnl8-1: 
1-8 days; for the P. desertorum colonies the ranges are D-Jn25-1: 
1-19 days; D-Jnl2-4: 1-21 days; D-J130-1: 1-4 days. 
Because P. desertorum and P. hyatti emigrated so frequently 
about 33% of the emigrations of both species were discovered in 
progress. These emigrations were readily noticed as hundreds to 
thousands of workers, most carrying brood, formed a column 
connecting the old nest to the new nest. The width of this column for 
P. hyatti was about 3 cm, while for P. desertorum the column 
tended to be wider (on one occasion reaching a width of 15 cm). 
Laboratory experiments have revealed that P. hyatti's emigrations 
