Nov., 1911.] Life-Histories of Syrphidae II. 399 



The anus is ventral on the last segment. 



These larvae were first taken at Columbus, Ohio, on May 31, 

 1911, when a dozen or more of various sizes were collected on 

 Curled Dock {Rtimex crispus L.) very badly infested with an 

 aphid (Myzus sp.). 



On June 4, eggs and larvae were taken from the same host, 

 the eggs hatching the following day. The young thus made their 

 first appearance at this station the latter half of May and the 

 first of June. At Lakeville, Ohio, seventy miles north-east, 

 larvae of differing sizes were collected from both Curled Dock and 

 Broad Leaf Dock {Rumex obtusijolius L.) June 15-18. At San- 

 dusky, on Lake Erie, larvae of this species nearly full grown were 

 collected from Curled Dock on June 21 and July 1. At Castaha, 

 June 29, larvae were abundant on Common JBurdock {Arctium 

 minus Schk.) On July 8 both pupae and larvae were taken in 

 considerable numbers from Burdock at Kelley's Island. Again on 

 August 27th larvae were found on thistle {Carduus sp.) at 

 Lakeville, Ohio, among aphids {Aphis sp.). 



From all the observations made on this species two distinct 

 generations seem evident : one appearing in spring at dates varying 

 from the middle of May to the middle of June or a Httle later in 

 different parts of the State, a second appearing in August and 

 perhaps later. 



On Rumex these larvae are to be found among the aphids 

 {Mvzus sp.) which cluster especially on the heads or flower 

 spikes and the smaller leaves ; on thistle on the upper tender parts 

 of stems; on Arctium they are more especially on the under side 

 of the large lower spreading leaves. They are parasitic on the 

 aphid colonies catching the individuals with their mouth-parts 

 and killing them by slowly picking out and sucking out all the 

 soft body-contents within the chitinous wall. During this 

 process the mouth parts are manipulated by strong muscles 

 which also move the large chitinous plates about the oesophagus 

 out and in like a battering ram. The anterior two or three seg- 

 ments are pushed inside the sac-like body-wall, and the contents 

 very carefully and completely picked out all around and into the 

 bases of the appendages. Empty skins are dropped and may 

 sometimes be noted. 



The larvae are sluggish when plenty of food is at hand, usually 

 nicely protected by position among the aphids and somewhat by 

 colors similar to those of the host plant. They can, however, 

 move actively by looping movements with the assistance of the 

 pro-legs. When in search of food the larva advances a short 

 distance, raises the anterior half of the body and lashes it rapidly 

 from side to side, then advances again and repeats the side lashing 

 until it touches the desired food. 



