316 



HABITS OF I.ARVAE 



The aquatic larvae feed upon algae, decaying vegetable matter, 

 and small Crustacea. The terrestrial species occur in a variety of 

 situations, some of them being found in nests of Hymenoptera, or in 

 those of rodents — where they act as scavengers ; others occuring under 

 loose bark of living or recently felled trees, feeding upon the sap, or 

 on dipterous larvae ; while still others feed upon decaying vegetation 

 or on manure. One genus (Hermetia) has been recorded as feeding 

 upon the dead body of a man. 



HABITS OF IMAGINES 



The species are most active on sunshiny days, some of them being 

 much given to settling upon leaves of trees which are in full sunlight. 

 Most species frequent flowers, especially those of Umbelli ferae, feed- 

 ing upon the nectar, and are particularly numerous on marshy ground 

 or along the margins of streams, ponds, or other bodies of fresh 

 water. Few species occur on the seashore and I know of none that 

 that are found in the larval stage in salt water. 



The eggs are usually laid in masses on the leaves of aquatic plants, 

 as shown in Figure 4, Plate XLVII. 



Key to Subfamilies 

 larvae and pup aria 



1. Apical abdominal segment very much longer than broad and very 



distinctly tapered, but if the length is not over 3 times that of 

 the basal width the antepenultimate and penultimate ventral 

 segments have each 2 or 4 stout curved thorns on their posterior 

 margins; posterior spiracnlar chamber at apex of last segment, 

 the margin armed with numerous soft, plumose or pubescent 

 hairs; aquatic species Stratiomyiinae (p. 317). 



— Apical abdominal segment not over twice as long as its basal width ; 



if the species is aquatic and has the posterior spiracnlar chamber 

 armed with marginal hairs the ventral thorns are absent 2 



2. Aquatic species ; bristles on dorsum paired, very short, sometimes 



thickened apically; posterior spiracnlar chamber margined with 



long, soft, plumose or pubescent hairs 



Clitellariinae, pt. (p. 322) . 



— Terrestrial species ; bristles on dorsum single, long and tapered, or 



in groups ; posterior spiracnlar chamber on dorsum of apical seg- 

 ment, transverse, not margined with soft hairs 3 



3. Each segment with a deep notch in each lateral margin slightly be- 



fore middle, dividing the segment into 2 unequal lateral lobes 

 (PI. XLIX, Fig. 11) Genus mccrtns 1 (p. 344). 



