1967] Willey & Willey — Populations of Grasshoppers 
45 
west. However, this varies from year to year with too many variable 
factors involved to be very meaningful. There is no observable 
difference in vegetation or climate between the two rims which also 
are nearly identical in elevation. 
To the south, west and north the area is surrounded by arid barren 
lands (“Dobe Hills”) and irrigated farms, areas in which A. con- 
spersa has not been found. The primary Gunnison uplift continues 
to the continental divide on the east, however, with grasslands and 
forest openings favorable to maintaining large populations of the 
species. 
Arphia conspersa. This species is characteristic of the western 
Great Plains and foot hills of both slopes of the Rocky Mountains 
from Northern Mexico to the Canadian plains provinces. In all of its 
range it is springbrooded with the nymphs overwintering and 
emerging as adults a few weeks after the snow melts or at the onset 
of warm weather. Therefore the peak of population activity is alti- 
tude and latitude dependent. At the Black Canyon the peak in 
“typical” years occurs probably in late May at 6000 feet and is 
delayed until mid- June or later at 8000 feet on the rims of the 
canyon. The phenology is dependent on the “lateness” or “earliness” 
of the season as well. The population at 8000 feet reached its peak 
during the second week of June in 1966 and the last week of June in 
1965 — a heavy snow year. 
Our studies of this species’ behavior are not yet published; there- 
fore a brief summary of its biology is in order. Arphia conspersa is a 
remarkably sedentary species, considering its flight capabilities and its 
active behavior. Its low vagility (Allee et al, 1949, p. 213) is prob- 
ably caused in part by complex social interactions which include short 
spontaneous flights, primarily by the males, only 6 to 10 feet in 
length. During these flights the wings make a buzzing sound or 
crepitation. Adult males and females tend to gather in interacting 
sub-deme groups. The size of each cluster is seldom more than 100 
to 200 feet in radius regardless of the extent of the suitable habitat. 
Seldom does the density of the male population reach 60 per acre even 
in the clusters; 10 to 20 males per acre in suitable habitat is the 
usual population. Females are more sedentary and seldom fly except 
as young adults. 
Cloudy, windy weather suppresses flight activity markedly. These 
insects often become so immobile that they can be picked up by hand 
— if they can be found. Arphia is a relatively small grasshopper and 
there is little heat storage in its body. Slight meteorological changes 
register quickly on the activity of the population. At air velocities 
