THE LOCUSTS. 137 



great interior region between the Wasatch and the Sierras over 

 much of its territory will be found to harbor a few during most 

 years. W henever, therefore, over these regions the conditions are 

 favorable they increase to astonishing numbers. These favoring 

 conditions are exceptional dryness and warmth. If two such 

 seasons follow each other in the native habitat of the locust they 

 are sure to migrate. 



Their Spring History and Migration. After they hatch out in the 

 spring it takes about seven weeks before they reach their full 

 growth. During this time they moult five different times, and 

 each time change slightly in color. Only at the last moult are full 

 wings acquired, the thorax flattened and the insect ceases to grow. 

 Where now they cover the ground in their native haunts from their 

 abundance the scanty vegetation is soon exhausted. It is now that 

 they manifest their peculiar instincts. They take short flights for 

 several weeks, apparently to test and strengthen their newly ac- 

 quired wings. The warm pleasant days with gentle winds are the 

 favorable peiiods for flight. When all is in readiness they rise 

 from eight to ten o'clock in the forenoon and move ofF with a 

 rapidity dependent on the wind, varying from three to fifteen miles 

 an hour. They do not move in broad sheets, but in columns like 

 fleecy clouds from one to five thousand feet thick. They some- 

 times continue their flight through clear, warm, moonlight nights, 

 but more generally come down between three and five o'clock to 

 feed. On the following day they continue their flight if the weather 

 is favorable. A change of wind or fall of temperature brings them 

 to the ground at any time. From their native habitat they move 

 mainly in an easterly, southeasterly, and southern direction. 

 Moving in this direction those that commence migrating from 

 Montana by the middle of July reach Nebraska and Kansas some 

 time in August or September. They do not always deposit their 

 eggs where they first light down. Frequently they remain from 

 one day to three weeks and then move farther on before egg laying- 

 is commenced. 



The Numhers that Light Down is often enormous. In 1866 in 

 Cedar County, during Julv, they appeared in such numbers that 

 the sun was darkened. The limbs of trees bent down and broke 

 under their weight. It was exceedingly difficult for one to move 

 through the living mass. Others have had, and reported similar 

 experiences. It is true that such cases are extreme and exceptional, 



