350 THE LOCUST 



pie, the young hatch in May or June, depending upon the season. 

 Within a few hours the migration begins. The grasshoppers travel 

 toward the sun as long as it shines. If a cloud passes, they stop 

 and gather in clusters in the dryer places. In cold or rain, they 

 crawl under anything available or into crevices in the ground, until 

 they may seem to have entirely disappeared, but they reappear 

 with the sun. In parts of the foothills where it rains lightly on 

 many afternoons, they will, therefore, follow the morning sun 

 more than that of the afternoon and tend to travel in a south- 

 easterly direction ; but the distance and rate of the migration and 

 even its direction is indefinite. As the wings have not yet devel- 

 oped, locomotion at this stage is effected principally by crawling 

 rapidly over the ground, although the air is filled with hopping 

 individuals as the swarm moves forward. When they happen 

 to cross a cultivated field the plants are eaten even to the roots, 

 yet the swarm passes on its march to what may be barren territory 

 beyond, without destroying the grain that may stand on either side. 

 At the time of the final molt when the larvae are ready to be trans- 

 formed into the adult, the individual stops and clings to some 

 upright stem until the skeleton is cast and the wings are suffi- 

 ciently dried for flight. The possibility of a high rate of increase, 

 which is ever present in the grasshopper as in other insects, is, 

 however, reduced to a minimum by various checks that keep the 

 numbers within bounds save in exceptional seasons. The factors 

 of the physical environment that are thus effective as checks upon 

 increase are moisture and temperature, since the young will not 

 develop in large numbers except in a dry, warm season. Fre- 

 quent freezing and thawing also destroys the eggs in winter. 

 Large numbers are destroyed by enemies and parasites. Mice, 

 ground squirrels, moles, and skunks dig for the eggs. Insectivo- 

 rous birds and also toads, Hzards, snakes, and skunks devour large 

 numbers of the young and adults. The larvae of blister beetles 

 are by far the most important insect enemies of the grasshopper 

 (Fig. 173). These beetles lay their eggs in the ground, where they 

 soon hatch into active larvae with powerful jaws which seek out 

 the grasshopper egg-masses, burrow into them, and begin to 

 devour the eggs. Larvae of bee-flies are a less important enemy 

 of the same sort. 



Among the parasites of grasshoppers is an insect that lays its 

 eggs with the eggs of the grasshopper. In accomplishing this, the 



