270 BULLETIN 31, UNITED STATES NATIONAL MUSEUM. 



most coiiveuient collecting-bottle that I have used, consists of a plain, 

 ■widemonthed, small bottle, lined throughout with blotting-paper, in 

 the firm cork of which a small cavity is filled with blotting-paper wet- 

 ted with a solution of cyanide of potash. For a collecting-net I would 

 recommend coarse bobbinet lace, attached to a light wire ring eleven 

 inches in diameter, with a light, rather short handle. 



LAEV^. 



The earlier stages and metamorphoses of many of the European species 

 of Syrphidse are known, and very similar habits and structural peculi- 

 arities may be expected from the American species when they shall 

 have been more studied in the larval and pupal conditions. Very few 

 species hitherto have been observed in the United States, and they offer 

 no novelties in the general known habits of the family. The larvae live 

 usually upon vegetable substances, though some are partly or wholly 

 parasitic upon other insects, especially the Aphidse, which they serve 

 largely to keep in check. Some are aquatic, living in mud, outhouses, 

 vegetable mold, breathing through the elongate stigmatic tube at the 

 hind end of the body, which they protrude from the substances, when 

 very moist, in which they live. Other species live under bark, on leaves, 

 in the nests of bees, ants, etc. 



The larvsB are usually not very elongate, with firm, sometimes tough 

 skin, the head segments small and extensile. Like the other families 

 of the Cyclorrhapha, the larvae of Syrphidse do not have a distinctly 

 differentiated head. The external mouth parts are either wholly want- 

 ing, with only a soft fleshy opening, or there are two or four outwardly 

 directed hooklets. There are also short, small, one or two jointed fleshy 

 antennai. The body is smooth, or provided with soft, conical projections 

 and bristles : below usually with seven pairs of abdominal feet. At 

 the posterior end, the body terminates in a more or less elongate tube, 

 single or double — the stigmata. This sometimes forms a short, almost 

 chitinized, tubercular projection on the dorsal part of the last segment ; 

 at other times it is very long, longer than the body, slender, composed 

 of two joints, the one sliding within the other, like the joints of a tele- 

 scope. It is never divaricate, or forked at the tip, as in many of the 

 other tailed larvae in the allied families. In changing to the pupal con- 

 dition the larval skin contracts, as in all of the Cyclorrhapha, to form 

 the pupal envelope, and the body becomes shorter, more oval, and of a 

 darker color, the elongated respiratory type, in the " rat- tailed " species, 

 being curved over the back. At the expiration of the pupal period the 

 anterior end of this envelope is pushed off by the inclosed insect and 

 the perfect fly escapes, soft and moist, but in a very short time in the 

 sunlight to acquire strength and firmness. Unlike all the other Cy- 

 clorrhapha, except the Pipunculidae, however, the frontal lunule in this 

 family does not subserve the usual purpose of springing ofl" this trap or 

 lid to the larva's prison, for it is fused with the front and not inflatable. 



