Mar., 1912.] 
Life-Histories 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 chcmotropism 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 larvae 
grasp first a leg or antennae of the aphid and cling to it until they 
can reach the thorax or abdomen. 
A young, one-day-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 unable to escape. 
These younger larvae do not eat rapidly. 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 8 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 brassicee. 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 minutes 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. 
