23 
in the temporary region, especiall} 7 in early summer, instinctively fly 
to the north or northwest, and do not extend to do damage farther east. 
Those, also, which acquire wings later in the summer in more northerly 
regions, and which fly more to the south, never extend any great dis- 
tance east of where they hatch j those developing on the eastern con- 
fines of the species' range (see map) passing south westwardly, and those 
Fig. 3. — Caloptenus spretus, anal characters of male ; a, from above : b, from the side: c, from below; 
enlarged six times (Emerton del). 
born toward the mountains southeastwardly. In 1875, a few stragglers 
were carried as far as the center of Missouri, by being swept into the 
Missouri Eiver, and drifting on logs and chips during the annual rise 
in July. But whenever scattering individuals' are carried in this or 
any other way beyond the eastern limits we have laid down, they soon 
perish. Most of them are diseased or disabled, and if they lay eggs, 
these hatch in the autumn and perish at the approach of winter. 
Bate at which Locust Swarms move.— The rate of migration of the 
winged insects will depend entirely on circumstances. The history of 
the past years of invasion shows conclusively that the rate of progress 
of invading swarms from the permanent breeding-places will average 
about 20 miles a day. It is, however, exceedingly irregular and greatly 
dependent on the velocity of the wind. Bad weather may impede or 
adverse winds divert flight. 
One noticeable feature of the invasions, is the greater rapidity with 
which the insects spread in the earlier part of the season, while in full- 
est vigor, and the reduction in the average rate of progress the farther 
east and south they extend. The length of their stay depends much 
upon circumstances. Early in the summer, when they first begin to 
pour down on the more fertile country, they seldom remain more than 
two or three days ; whereas, later in the season, they stay much longer. 
In speaking of the advent and departure of these insects, I use relative 
language only. The first comers, when — after having devoured every- 
thing palatable— they take wing away, almost always leave a scattering 
rear guard behind, and are generally followed by new swarms ; and a 
country once visited presents for weeks the spectacle of the insects 
gradually rising in the air between the hours of 9 or 10 a. m. and 3 
p. m., and being carried away by the wind, while others are constantly 
dropping. 
