SYRPHIDAE OE MAINE. 205 



the fly are produced very gradually. The legs, mouth-parts 

 and wing-pads differentiate first while the dorsal part of the 

 body and especially the abdomen is still eruciform as in the 

 larva. Antennae and eyes next take form followed by the seg- 

 mentation of the abdomen the appearance of the vestiture and 

 the differentiation of the thorax. The hind leg during this 

 stage is bent at the middle of the tibia at an angle of about 150 

 degrees. The coloration of the adult is well developed some- 

 times several days before emergence ; and in species where the 

 puparium is quite transparent it is often possible to identify the 

 species through the puparium. 



(4) The Adult. When fully formed the adult pushes off a 

 lid-like portion of the anterior end of the puparium by the dila- 

 tion of its face and crawls out of the opening so formed. 

 Emergence often requires several hours' time and not infre- 

 quently a specimen dies in the attempt to disentangle itself from 

 the puparium. By the time emergence is accomplished the insect 

 has practically assumed the adult form. The principal differ- 

 ence is that the wings are thick, crumpled and folded (Fig. 32- 

 54) and must expand to a much greater area, become flattened 

 instead of bag-like and hardened to form an effective organ of 

 flight. The coloration of the fly is pale and the whole body 

 somewhat soft and worm-like. But within an hour, sometimes, 

 indeed, within a few minutes, the body has become perfectly 

 indurated, the wings completely expanded, and the color-mark- 

 ings fixed to that of the imago. 



After emergence the life of the fly is dominated by two im- 

 pulses, the instinct to feed and the instinct to reproduce its 

 kind. The food of the adult is practically always secured from 

 flowers and consists of nectar and pollen. The flies seem to be 

 strongly influenced by heliotropism or sunlight. They are almost 

 always active in the sunshine and the brighter and warmer the 

 day the more active they become. These facts may be taken 

 advantage of by the person who wishes to collect Flower-flies. 

 The most fruitful collecting is to be found about melliferous 

 flowers and in the sunshine, particularly in very early spring. 



Mating may take place on the wing with both sexes actively 

 flying (hovering) and oriented in the same direction, the male 

 uppermost (Sphaerophoria, Sphegina, etc.) ; or the pair may 

 come to rest on foliage, in which case the two are usually facing 



