INVADING SWARMS USUALLY COME FROM NORTHWEST. 75 
1865. — Locusts flew into Minnesota from the west and northwest. 
1866. — There was a general invasion from the west and northwest, which reached 
to Texas. 
1868. — Locusts appeared in Riley County, Kans., from a northerly direction, the 
exact direction not clearly ascertained. 
1873. — Locusts entered Texas in September from the north. 
1874. — This was a very general invasion, and all accounts show that the flights were 
from the northwest. 
1875. — Eagle Pass, Texas, was visited by swarms, moving from the north, in Sep- 
tember. From Dakota the locusts migrated from the middle of July until the middle 
of August, moving south or southeast. But there appears to have been no general 
invasion of the intermediate States and Territories. 
1876. — There were fresh arrivals in Texas from the north and northwest. During 
the same year Missouri, Kansas, Nebraska, and Iowa were visited by heavy swarms, 
always coming from the northwest. 
Some of the swarms this season were traced back nearly or quite to the borders of 
Montana, at least to the northwestern portion of Dakota. 
This is conclusive as to the direction from which invading swarms 
usually arrive in the temporary region, but before it can be made con- 
clusive of the proposition, and of value in studying the life history of the 
species, it is necessary to eliminate two possible explanations which may 
be given without recourse to the hypothesis advanced. 
First. It may be contended, as the writer and Dr. Scudder at one time 
held, following the idea advanced by Keferstein, Zinnani, Schrank, Kop- 
pen, and some other European entomologists, that these invasions may 
be from points much nearer the place of arrival than generally supposed 
and indicated in the above proposition. For illustration, may not the 
swarms that reach Texas come from Eastern Colorado or Indian Terri- 
tory ; those arriving in Kansas, from Western Nebraska ; those reaching 
Nebraska, from Southwestern Dakota, &c, thus moving on in successive 
waves, each wave representing a generation ? And is it not more than 
likely that the circumstances which cause excessive multiplication at one 
of these poiuts will have the same effect in the other, when these circum- 
stances operate generally over a large area, as in 1866, 1874, and 1876, 
and hence the movements be apparently the same as if all the swarms 
came from the permanent region of the northwest ? 
Secondly. As it has been ascertained that the invading swarms sel- 
dom arrive earlier than July, and often as late as August and the first of 
September, and as those locusts hatched in Texas become full-fledged in 
April and May, those of Kansas in May and June, and those of Nebraska 
in June, and almost universally fly northward soon afterwards, may not 
the invading swarms be the same that moved northward, again return- 
ing southward ? 
The second supposition is easily disposed of. That " returning swarms," 
or swarms flying from the temporary region northwest, toward the per- 
manent area, do often change their course and again move south, and 
are sometimes taken for " invaders," is certainly true, as we know from 
dara collected in 1877. But this will not apply in years when no swarms 
