24 
In short, the rate of spread is greatest during the first 10 or 15 days of 
their winged existence, or before the females become occupied with egg- 
laying. The invading insects are then passing the extensive plains aud 
thinly settled regions of the Northwest, where there is little inducement 
for them to halt, and the rate at such times, with strong and favorable 
wind, may reach a maximum of from 200 to 300 miles a day. 
The rate of spread of departing swarms from the temporary region is 
very much the same. It is most rapid and direct early in the season 
when the insects first begin to leave more southern latitudes, and be- 
comes more slack and inconstant as summer advances. 
Extended flight does not take place till 4 or 5 days after the first in- 
sects become winged. For the first 2 or 3 days the newly-winged indi- 
viduals mingle with the larvae and pupae, eating ravenously and making- 
short flights of a few yards or more, as if to try their wings, recalling fully 
the habit of native nonmigratory species. Then for a while they rise 
one by one higher in the air and float along with the wind, and finally, 
when weather and wind are favorable, all that are strong and mature 
enough rise as with a common impulse during the warmer morning hours 
and move off vigorously in one direction until they are soon out of sight. 
They begin to rise when the dew has evaporated, and generally descend 
again toward evening. A swarm passing over a country yet infested 
with the mature insects constantly receives accretions from these, and is, 
consequently, always more dense in the afternoon than in the forenoon. 
In rising the insects generally face the wind, and it is doubtful if they 
could ascend to any great height without doing so. 
The velocity of flight, which, for many reasons, is quite distinct from 
the general movement understood by u rate of spread " or u migration," 
is naturally greater and will average about 10 miles an hour. It is also 
greatly dependent on the wind. Mr. S. S. Clevenger, of New Auburn, 
Minn., gives the average rate at 15 miles for that locality ; while the 
reports of other correspondents give the range from 4 to 40 miles, the 
more common rates mentioned being 12, 15, and 20 miles per hour. 
Mr. Brown Lusted, of Winnipeg, Manitoba, tells us that in 18G7, when 
he was traveling from Saint Cloud, Minnesota, to Manitoba, the locusts 
were moving in the same direction, at from 30 to 35 miles a day. Pro- 
fessor Aughey's observations for 1877 give the rate per hour at 4 milt s 
and upward ; but he has himself expressed to us the belief that his 
estimates are somewhat low. We have ourselves never witnessed 
them flying so slowly as 4 miles per hour, which must be considered 
the minimum rate where there is no impediment. When tacking 
against the wind, they may move not more than 1 mile, while the maxi- 
mum rate, in a strong wind, may reach as high as 50 miles or more per 
hour. 
Direction of invading Swarms. — While there may be, during an inva- 
sion, local flights in all possible directions (except, perhaps, due west), 
the general movement east of the mountains is conspicuously toward 
