216 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



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." 



In short, the rate of spread is greatest during the first ten or fifteen 

 days of their winged existence, or before the females become occupied 

 with egg-laying. The invading insects are then passing the extensive 

 plains and thinly-settled regions of the I^orthwest, 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 two to three hundred 

 miles a day. 



The rate of spread of departing swarms from the temporary region is, 

 as may be gathered from Chapter YII, 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 becomes more slack and inconstant as 

 summer advances. 



Extended flight does not take ijlace till four or five days after the first 

 insects become winged. For the first two or three days the newly- 

 winged individuals mingle with the larvse and pupse, eating ravenously 

 and making short flights of a few yards or rods, as if to try their wings, 

 recalling fully the habit of native, non-migratory 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 till 

 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 ^'rate of spread" or "migration,'? 

 is naturally greater and, will average about 10 miles an hour. It is 

 also greatly dependent on the wind. Mr. S. S. Glevenger, of ^ew 

 Auburn, Minn., gives the average rate at 15 miles for that locality (App, 

 22); while the reports of other correspondents (App. 13) 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 Winnepeg, Manitoba, tells us 

 that in 1867, when he was traveling from Saint Cloud, Minn., to Mani- 

 toba, the locusts were moving in the same direction, at from 30 to 35 

 miles a day. Professor Aughey's observations for 1877 (App. 8) give 

 the rate per hour at 4 miles and upward ; but he ha^ himself expressed 

 to us the belief that his estimates are somewhat low. We have our- 

 selves never witnessed them flying so slowly as 4 miles per hour, which 



