35 o ECONOMIC ENTOMOLOGY. 



quently found in privies or cesspools, sometimes appearing so 

 suddenly and in such numbers that a suspicion is engendered 

 that the specimens have been passed by the individuals using the 

 out-house. In fact, I have on more than one occasion received 

 the larvae with the positive statement that this had actually 

 occurred. They are curious creatures, maggot-like in general 

 shape, with a long, extensile, tail-like appendage at the anal ex- 

 tremity. It is hollow or tube-Hke, and at the end is a spiracle, 

 the use of this telescopic tail being simply to keep the opening 

 above the surface of the filthy mass in which the insect lives, and 

 thus to secure a supply of pure air. The 

 Fig. 401. larvae are called from this peculiarity " rat- 



tailed." The reason why the flies are 

 ^^^^^^^^^^V sometimes so abundant in greenhouses is 

 '^^i^^^^^^^ that somewhere in their vicinity, among 

 Rat-tailed larva of ^rzj^afe. semi Hquid mauurc, the best breeding- 

 places can usually be found. Taken as a 

 whole, this family Syrphidcs contains no really noxious insects, 

 and many that are decidedly beneficial. It should be noted, 

 however, that the larvae of some species feed upon pollen, and 

 that others live in growing vegetable tissue ; hence it is not 

 impossible that in the future this general statement may have to 



Fig. 402. 



Mesograpta poHta. — Larva, pupa, and adult; all enlarged. 



be modified. One of the most common Eastern species, Meso- 

 grapta polita^ has been found feeding in great numbers in the 

 larval stage upon corn pollen, but without causing any real injury. 



Passing over several small families interesting enough in them- 

 selves, but not of importance to the agriculturist, we reach the 



