Mar., 1912.] Life- Hi stories of Syrphidae III. 481 



The ventrum of the body is bare; seven pairs of ventral folds 

 of the body-wall making fairly well-defined prolegs. 



The larva emerges from the egg very slowly. The anterior end 

 of the egg splits and the sides spread under the contractions and 

 expansions of the larva. Then by stretching out and clinging to 

 some object it pulls itself out little by little. The egg shell is 

 tough rather than rigid and yields to the contortions of the larva. 



When first hatched the larvae are inactive and will lie quietly 

 for hours if undisturbed. If an aphid is forced upon them they 

 will often attack it and attempt to eat it frequently with the result 

 that they are carried away by the larger insect and finally dis- 

 lodged. However, after the lapse of eight or ten hours the larvae 

 begin active crawling movements in search of food. Apparently 

 their prey is located not by a chemotropism but by thigmotropism 

 as they frequently pass by an aphid so closely as almost to touch 

 it and go on in search of others. The characteristic movements of 

 these larvae when searching for food are familiar to many and have 

 been described for another species (l. c). Frequently the larvse 

 grasp first a leg or antennae of the aphid and cling to it until they 

 can reach the thorax or abdomen. 



A young, one-da^'-old larva barely a millimeter and a half long 

 looks preposterous attacking an aphid fully three times its size. 

 Yet so firmly does the larva cling or become cemented to the surface 

 by its posterior end that the aphid is tmable to escape. 



These younger larvs do not eat rapidh\ I have at various 

 times observed them in one place sucking the juices of a single aphid 

 for from a half to two-and-a-half hours. Sometimes the aphids 

 continued to struggle for an hour or more. 



Growth is rapid. By the end of the second day some of the 

 specimens had reached a length of 7 or S mm. and a width of 

 1.2 mm. 



In order to determine something of the capacity of these insects 

 for devouring plant lice and hence their degree of economic 

 importance, the writer tried feeding them with cabbage aphids 

 {Aphis brassiccB. Linn.) The aphids were touched to the mouth 

 of a larva which had not been kept from food. A four day old 

 larva devoured the first aphid in 4.5 minutes, a second, third, 

 fourth, and fifth smaller than the first in 2, 1, 1, and 0.5 minutes 

 respectively. The sixth a larger one was retained for 3.25 minutes. 

 These were very thoroughly eaten, all the viscera and body 

 fluids being picked and sucked out. After this the lice tendered 

 were not eaten so closely, but killed, a seventh in 2 minutes an 

 eighth in 1.75 ininutes and a ninth in 1.5 minutes. 



On another occasion the same test was made with an older 

 larva which devoured a dozen or two before the writer's patience 

 became exhausted. The tests were sufficient, however, to establish 

 the voraciousness of the appetites of these larvae. 



