26 OHIO BIOLOGICAL SURVEY 



led to a close, obligate predatism on aphids in galls, and there has been 

 reported a case of internal parasitism. Still others live in nests of certain 

 Hvinejioptcra. 



The kind of food varies as much as the habitat, from living 

 plant tissues or sap thru decaxing wood, to all kinds of deca3dng organic 

 matter or excrement; and, on the other hand, to living soft-bodied insects. 

 So far as I know none of the aquatic larvae have been observed to feed 

 on minute animals or plants, except possibly on algae (see pp. 46,70). 



Some of the aphidophagous species seem to be rather omnivorous. 

 The larvae of Syrplms ainericanics a.n6. Allograpta obliqiia, which have been 

 rather more carefully studied in this respect than the others, were each 

 found preying on three to six different species of Homoptera. Didca 

 Jasciata on the other hand was found, in the larval stage, preying only 

 on one species {Longistigma caryae) of Aphididae, and the gall infesting 

 species seem to be essentially restricted to one species of prey. 



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 

 man}' people. When used for progression alone, these movements maybe 

 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. Thigmot- 

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

 Hungry larvae frequently pass b}^ 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 until 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 pick- 

 ing and sucking out all the body contents, which may continue from a few 

 minutes to more than an hour (in the case of ver}' 3^oung larvae). The 

 action of the mouth-parts is very characteristic 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 eso- 

 phageal frame-work, the jaws, and the mouth-hooklets. Some of them 

 operate, the framework in and out like a battering ram. Others at the 

 same time open and close the jaws. The anterior two or three segments 

 are inserted completely within the body wall of the aphid. The jaws are 



