THE INSECT WORLD. 



383 



that infest aphids. If, at any time during the summer, a leaf 

 badly infested with plant-lice be examined, there will be usually 

 found a few specimens that seem abnormally swollen and livid 

 gray in color rather than green or yellow. Such specimens are 

 parasitized, and if they be removed to a closed vessel, there will 

 be found in it, in a few days, minute blackish or brown wasp-like 

 creatures, and on each of the infested plant-lice will be seen a little 

 round hole, which shows where the insect emerged. They are 

 usually examples of minute Braconids, and are the most im- 

 portant of those natural checks that prevent the increase of plant- 

 lice above a certain point. Unfortunately, that point does not 

 coincide with the hmit at which the insects become injurious to 

 the farmer ; hence, though the parasites accomplish their pur- 

 pose, they do not, therefore, confer any direct benefit upon him. 



At almost all periods during the season, but especially late in 

 summer or fall, caterpillars may be seen, bearing upon their 

 backs and sides white or yellowish, egg-shaped bodies. These 

 are often supposed to be the eggs of the caterpillars, but as a 

 matter of fact they are cocoons of Microgaster or Apanteles, 

 little parasites belonging to this family ; and if the caterpillar be 

 confined for a few days it will be noticed that from the tips of 

 each of these egg-shaped bodies a little circular lid is lifted off 

 and a little wasp emerges. If, late in summer, a number of the 

 large sphinx caterpillars infesting potato or grape-vines are 

 watched when they yet show no signs of infestation, one may fre- 

 quently see the little larvae boring their 

 way through the skin, wriggling until 

 they have emerged for more than half 

 their length, and it is then easy to 

 watch the formation of the small silken 



rx-ii -11 1 Sphinx larva covered with Mi- 



cocoons. The caterpillar soon becomes crogaster cocoons, 



an odd-looking sight, with anywhere 



from a dozen to fifty or even a hundred of these little maggots, 

 all engaged in spinning cocoons, projecting from it in every di- 

 rection. The egg-like cocoons are attached merely by a little 

 point, so that they may be easily removed. But the caterpillar 

 has been drained of its strength and of the substance for the for- 

 mation of the future butterfly : it collapses and dies, unable to 

 complete its transformation to the pupal stage. 



