DIPTERA. 341 



or wanting in Nemocera ; and the winglets, undeveloped 

 in Nemocera, are often conspicuous in Brachycera. 



The habits of Flies both in the larval and perfect states 

 vary much. Of the larvse, many are purely aquatic, as the 

 well-known active little Gnat larva common in all pools, 

 ponds, and tanks ; or live in wet mud and filth, as the 

 useful " rat- tailed " larva of the Dronefly. Others live in 

 the earth, feeding on decayed matter, or on the roots of 

 plants ; while some, as the " Gentle " of the angler, are 

 deposited, already hatched from the egg, in the carrion 

 which it is their office to consume.* They are found 

 feeding in almost every part of almost every kind of 

 plant, and a large number live in unhealthy growths 

 upon plants similar to the galls of the Hymenoptera 

 occasioned by their own presence. Some few feed upon 

 other living insects. Some, again, are parasitic, in- 

 habiting the nests and feeding on the food of other 

 insects ; while others, as the Gadflies, are parasitic within 

 the bodies of quadrupeds. 



The variety of food chosen by various Flies when 

 arrived at perfection is nearly as great as that of the 

 larvae. While perhaps the greater number of species 

 feed on the honey in flowers, and on the various juices 

 of plants, others, as the Gnats, Horseflies, c., suck the 

 blood of men and animals whenever an opportunity 

 offers. There are also true parasites among the FHes 

 species which, winged or wingless, live constantly, in 

 the complete state, upon the bodies of birds and quad- 

 rupeds. Besides these, many Flies are predaceous, 

 attacking other insects and draining them of their 

 blood, and some few live upon the fetid juices of carrion. 



* The value of this provision in the saving of time, when the object is 

 to check the evil effects of putrefaction, needs no remark. 



