SYRPHIDAE OF MAINE. 243 



seven the body tapers evenly almost to a point at the mouth-parts, 

 when extended ; when at rest the anterior three segments retracted and 

 rounded off at segment four. 



In their natural habitat the larvae were so covered with threads of 

 flocculence from the aphid host as to appear light grayish in color. 

 When this matter is removed the color is yellowish brown, consid- 

 erably mottled with black. The most conspicuous black markings are 

 due to masses of body fluids showing through the integument; but 

 others are formed by particularly thick areas of the black integumental 

 spines which cover the entire dorsum, but are so minute on the venter 

 that the latter appears bare. The largest of these spines about .04 mm. 

 long. The arrangement of these spots is shown in figure 34-1, where 

 only the ones due to integumental spines are shown. There are nine 

 such areas on each somite, three on the middle line and three at each 

 side. The integument is folded transversely, there being about five 

 folds to each somite on the dorsal side. On the ventral side in 

 segments five to eleven, inclusive, are nude elevations suggesting 

 prolegs. The segmental spines are situated on moderate, conical eleva- 

 tions and are about .10 to .15 mm. in length, but light in color. The 

 head segments bear the antennae and mouth-parts of the kind usual in 

 aphidophagous larvae. There is a pair of very heavy, black, lateral 

 mouth-hooks. The anterior larval spiracles on the third segment 

 (Fig. 34-1) are barely visible to the naked eye. When magnified 

 (Fig. 34--?) the surface is found to bear about a dozen, elongate nodules 

 arranged in a semi-circle. 



The posterior larval spiracles are unique among aphidophagous larvae 

 so far observed. They are borne on a very short, double process rather 

 more than usually emarginate distally, about half a millimeter broad, 

 .25 to .33 mm. long and about .33 mm. high. The slit-like spiracles 

 instead of being nearly straight are remarkably and irregularly sinuate, 

 convoluted or undulated in a very ornamental manner as shown in 

 figure 34-3 and 4. This extensive convolution makes the length unusu- 

 ally great for the spiracles in this type of larva. Between the spiracles' 

 the surface of the tube is deeply constricted so that each is situated 

 along the summit of a broadly rounded carina, the most dorsal one 

 the most prominent. The circular plate is only moderately conspicuous, 

 about .055 to .075 mm. in diameter, their inner margins .08 to .1 mm. 

 apart. The inter-spiracular ornamentation consists of small, blunt, 

 rounded knobs sometimes double, entirely inconspicuous. 



On several occasions larvae of this species were noted extrud- 

 ing from the anus on the ventral side of the caudal segment, 

 four finger-like flabellae similar to those previously described 

 for Eristalis aeneus (34, p. 86) but not heretofore noted among 

 aphidophagous larvae. Buckton (8) considers that these organs 

 have a renal function. 



