74 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
Our somewhat full, though far from complete, account of flights in our 
First Report will render it unnecessary to state much that might appear 
to be required in a full discussion of locust migrations ; we therefore refer 
the reader to that report to till out such lacunae as appear here. 
In studying the subject of flights, Ave have found it convenient not 
only to note such points or subdivisions as the mode of flight, direction 
of flight, density and extent of swarms, distance over which they move r 
date of flights, hours of rising and alighting, the height at which they 
fly, rate of movement, meteorological influences, as effect of wind, rain, 
heat, &c, flights at night, cause of flights, &c; but also, in the case of 
our locust, to distinguish between invading swarms, returning swarins r 
and local flights. As we may have occasion to make frequent use of the 
latter terms, we will explain them first, adding, at the same time, what 
we may have to say in reference thereto. 
1. DIRECTION OF MOVEMENTS. 
A careful study of the migrations of the Rocky Mountain locust for 
some years past has revealed the fact that the general or combined 
movements of this species, so far as the direction or course is concerned, 
may be designated by the three terms, Invading swarms, Returning 
swarms, and Local flights. 
a. Invading sicarms. — This term, when used with reference to the 
movements of C. spretns east of the mountains, applies to those swarms 
or hordes which move down from their native hatching grounds in the 
west and northwest into those sections where they are not in any sense 
permanent residents. It is only applied to those which, leaving the 
permanent area, pass across its boundary into the temporary regions 
shown in our map. 
The facts showing that the swarms which invade the temporary region 
come from the permanent regions of the west and northwest are so nu- 
merous and have been so fully presented in our former report that it is 
unnecessary for us to dwell on them at any length at this time, as we 
have but bttle to add that is new in reference thereto. It is true that 
but few swarms have been traced from their points of departure in the 
permanent regions to their stopping places in the temporary section j 
yet the circumstantial evidence is so strong as to no longer admit of any 
reasonable doubt. 
This evidence may be briefly summarized as follows : 
First. That the invading swarms, especially in years when eggs hav 
not been deposited the previous season, are very generally, if not always, 
observed in the temporary region east of the mountains to come fro-* 
the west or northwest, usually from the latter direction. The following 
brief summary from our former report Iri is strongly corroborative of thi 
assertion : 
1821. — Swarms of locusts entered Missouri from the northwest. 
1864. — Swarms entered Iowa and Minnesota from the northwest. 
Pape 148 et seq. 
