25 
the south and southeast. Tbe more local and irregular flights are gener- 
ally made for food, but the more extended southward movements are 
in obedience to other laws, discussed in Chapter XII of the Report and 
also on page 250. West of the main Rocky Mountain range the rule of 
flight appears to be from the higher plains and plateaus, Avhere the in- 
sect normally breeds, to the lower and more fertile valleys 5 and the 
greater irregularity of the prevailing winds an 1 more broken nature of 
the country preclude the same regularity in directions of flight that, on 
the whole, prevails east of the range. 
Time of Appearance of invading Swarms. — In endeavoring to deduce 
general conclusions respecting the time of year that the 1874 swarms 
reached different parts of the country, great difficulty was experienced 
in sifting those accounts which referred to the progeny of the 1873 in- 
vasion, and those which hatched within the insect's native range, and 
came from the extreme Northwest. The same was true of the fresh 
1876 swarms, and those which hatched in Minnesota. 
As a rule, the insects which hatch in the temporary region acquire 
wings and leave before the fresh swarms from the mountain region 
appear. In the more northern regions, as in Minnesoia and Manitoba 
westward, the insects hatched on the ground acquire wings the latter 
part of June and in July. The period is earlier as we go south, until 
in southern Texas they are able to fly in April. The time of appear- 
ance of invading swarms from the permanent region is in inverse ratio, 
i. e., earlier to the north and later to the south. Thus while on the con- 
fines of the permanent region it is almost impossible to distinguish 
between the insects which hatch there and the fresh swarms from the 
Northwest, the difference becomes more and more marked toward the 
south and east. 
In 1874, swarms appeared during June in southern Dakota; during 
July m Colorado, Nebraska, and Minnesota; during the latter part of 
this mouth in Iowa and western Kansas. During August they came 
into southeast Kansas and Missouri; and by the middle of October 
they reached Dallas, in Texas. In 187G they came later. 
Number of Broods. — Peculiarities of Habit. — The Rocky Mountain 
Locust, in spite of the fact that a second lot of eggs is sometimes de- 
posited in one season, is essentially single- brooded. This second depo- 
sition of eggs generally fails to hatch and arrive at maturity in time 
to reproduce the species. This follows from the fact that this locust 
is a sub-boreal insect and attains its greatest perfection only where 
the winters are long and cold and the summers short. The theory has 
been advanced that the object of the migrations of this species is to find 
a suitable region for producing a second brood; for instance, that a 
brood hatched early in the south moves to the northern limits of its 
range and brings forth a second brood. But it is a notable fact that in 
years of disastrous invasion from the northwest in late summer and 
autumn the locr.sts have not prevailed in the south during the spring. 
