APPLE LEAVES — SYRPHUS-FLIES. 101 



upon flowers. These flies drop their eggs, one in; a place, upon 

 leaves and twigs which are infested with plant-lice, so that -their 

 young may have their appropriate food immediately around theai 

 the moment they require it. One can seldom inspect many in- 

 fested leaves without meeting with one or more of the eggs of 

 these flies scattered around among the lice — little white smooth 

 oval bodies, much like the eggs which the hot fly glues to the 

 hairs of horses' fore-legs. From them a maggot hatches which 

 in its motions will remifld one of a leech or blood-sucker. It has 

 no eyes, and consequently cannot see in which direction to crawl 

 in search of its food; but fixing the hind extremity of its body to 

 the surface of the leaf, it reaches as far as it is able to stretch it- 

 self and feels around first upon one side and then upon the other. 

 If nothing is discovered it moves along one or two steps and again 

 feels all around, until finding a plant-louse it at once fixes its 

 tiny mouth at the slender-pointed anterior end of its body to it-s 

 prey, having such power of suctioh as not only to hold the louse 

 from escaping but to tear it away from its attachment and raise 

 it up in the air wholly away from the surface of the leaf The 

 louse sprawls its long legs about in a vain endeavor to touch some 

 support to enable it to escape. Its body is soon perceived to be di- 

 minishing in size, the worm sucking out the fluids which it con- 

 tains, and in a minute's time, or less, nothing of it remains but 

 an empty shrivelled skin. These Syrjr hus-worms are of various 

 colors, almost transparent and watery, or white, or greenish, and 

 comnionly clouded or spotted, particularly in the centre of their 

 bodies, with more opake white, yellow, tawny or red, and their 

 skin is so thin and transparent that the circulation of the fluids 

 within may be distinctly seen even with the naked eye in the 

 larger worms. Some of them have two cylindrical processes like 

 little straight horns jutting outtrom the hind part of their bodies. 

 One or more of these worms may almost always be met with 

 wherever a colony of plant-lice is located, and one medium sized 

 worm will consume a hundred of these insects in an hour. The 

 ants do not appear to molest them, but the aphis-lions, as already 

 remarked, devour them with avidity. When the worm has com- 

 pleted it^ growth it fixes itself to the surface of the leaf or the 

 barkj and contracts. to a shorter oyal form; its skin becomes hard 



