SYRPHIDAE OF MAINE. 215 



'These aphidophagous larvae, although frequently found entirely sur- 

 rounded by an abundance of prey, are very often obliged to search about 

 for food. Their characteristic, looping movements are very familiar to 

 many people. When used for progression alone, these movements may be 

 very rapid. Their progress is very similar to that of a 'measuring-worm' 

 though the body is not so long. When the larva is searching for food, 

 the anterior half or two-thirds of the body is raised in the air, very 

 much extended, and lashed from side to ,side. It is then attached and 

 the posterior parts pulled up, when the movement is repeated. Thig- 

 motropism, and not chemotropism, seems to be involved in locating food. 

 Hungry larvae frequently pass by aphids so closely as almost to touch 

 them, and go on in search of others. When a suitable aphid is found 

 the larva frequently grasps it first by the leg or antenna and clings to 

 this appendage unitil the thorax or abdomen: can be reached. The 

 mouth-parts are firmly attached to the body, the body-wall is punctured, 

 and the aphid usually lifted high in the air. Then begins a process of 

 slowly picking and sucking out all the body contents, which may con- 

 tinue from a fraction of a minute to more than an hour (in the case 

 of very young larvae). The action of the mouth-parts is very char- 

 acteristic and very well adapted to the needs of the case. Many different 

 muscles, which have their origin on the body-wall in the region of the 

 head, are inserted upon the cephalo-pharyngeal skeleton, the jaws, and 

 the mouth-hooklets. Some of them operate the framework in and out 

 like a battering ram. Others at the same tame open and close the jaws. 

 The anterior two or three segments are inserted completely within the 

 body wall of the aphid. The jaws are directed into every corner of the 

 body and even into the bases of the appendages as they pick and suck 

 out the soft contents. The skins, absolutely empty, are then discarded 

 by retraction of the segments, the hairs or spines on those outside serv- 

 ing readily to dislodge the skin. These dead skins usually drop down 

 or blow away but may sometimes be seen in numbers on the host-plant." 

 (The Author, 35, pp. 26, 27). 



2. As Scavengers. The other important way in which the 

 larvae of Syrphidae are beneficial to human interests is by their 

 activities as scavengers. Considerable quantities of dead animal 

 and vegetable matter are in this way reduced to simpler com- 

 pounds, more readily assimilated by plants; and certain ma- 

 terials which are obnoxious, and may be a menace to health, are 

 transformed to innoxious forms. 



To quote from Comstock (10, p. 415) : 



'^Although the habits of these creatures, which revel in all kinds of 

 filth are very disgusting, we cannot help admiring that arrangement by 

 which a mass of filth, instead of being left to poison the atmosphere, 

 is transformed into myriads of living beings whose swift flight an<J 

 delicate forms lendi life and beauty to the landscape." 



