248 Illinois State Laboratory of Natural History. 



to prefer the water and Strationiyia the shore. The 

 pupa is formed within the larval skin, which changes 

 y^v\ little, usually becoming slightly inflated. Only the 

 anterioi- part is occupied, the remaining space being 

 filled with air, causing the pupa to float at the surface, 

 where its thick larval casing protects the tender morsel 

 within. As the pupa matures the larval skin becomes 

 prepared to split transversely across the disk of the sec- 

 ond segment just over the face of the pupa, transversely 

 on the fourth segment, and on the median line between 

 these two, so as to form an I -shaped opening. Through 

 this opening, when formed, the fly emerges while its case 

 is floating on the water or resting on the shore. The 

 hibernating larvae and pupae may often be found in 

 large numbers under loose drift on shore, even at a 

 considerable distance back from the margin, emeiging 

 here in early summer. The adults are often common 

 about flowers, especially on low ground. They are prettily 

 marked with greenish or yellowish and black or brown; 

 and have a broad short abdomen, quite flat above. 



The life histories of the three species studied at Ha- 

 vana are quite similar. The early summer brood of flies, 

 derived from hibernating larvae, gives rise to a summer 

 brood of larvae, which probably produces a second brood 

 of flies in fall, as the abundance of very young larvae 

 in early spring is quite marked. 



KEY TO THi: GENERA OF STR ATIOMYITD.E. 



Three genera of this family are known to be aquatic 

 in habit. They may be distinguished by the following 

 charactei's : 



Last segment with a circle of plumose hairs sur- 

 rounding the stigmatal cleft ; head oblong-conic, 

 eyes at anterior third. {Stratiomyiince.) 

 Body acuminately narrowed posteriorly, last seg- 

 ment very elongate. [Fig. 57.] Stratiomyia. 



Body but little narrower posteriorly, last segment 

 not more tiian twice as long as its greatest width. 

 [Fig. 59, 60.] Od&ntomyia. 



