SYRPHIDAE OE MAINE. 



195 



ECONOMIC IMPORTANCE OF THE LARVAE 212 



A . Beneficial Habits 



(1) The larvae destroy myriads of aphids and arebelieved to be the 

 most important natural check on these destructive crop- 

 pests in the State ■ 212 



They sometimes occur in enormous numbers 212 



And may practically exterminate their prey in a given locality .212 



But are of most value in constantly and everywhere tending to 

 keep the aphids from increasing to seriously destructive num- 

 bers 212 



Several observations show their remarkable capacity for destroy- 

 ing aphids 214 



Their method of feeding is described 2 15 



(2) The larvae are of recognizable value as scavengers 215 



Their breeding in filth does not seriously endanger human health,, 



because they do not visit human food or human habitations 216 



B. Iniurious Habits. 



(1) The larvae of one species occasionally occur in great numbers 



on corn, sucking the sap and eating the pollen 216 



While two other European species, introduced to this country, 



feed in the bulbs of certain flowers and vegetables 217 



(2) The larvae which normally live in filth are occasionally intro- 

 duced alive into the human or animal alimentary canal, of 



other body cavities, causing serious functional disturbances 217 



The probable sources of such infectiDn to b? guarded agaimt ar^ 



noted . 218 



ECONOMIC IMPORTANCE OF THE ADULTS 219 



The adult Flower-flies are exclusively beneficial and of great im- 

 portance in pollenizing many fruit and shade trees, flowers, 

 and crops 219 



