The Two- winged Flies 339 



bee, with black head, yellow-brown thorax, and the abdomen blue-black 

 with yellow base. The full-grown larva is a large black spiny grub. 



One or two species of bot-flies infest man, and also (probably the same 

 species) monkeys and dogs and perhaps other animals. Numerous instances 

 are recorded in which the larvae of Dermatobia noxialis and D. cyaniventris 

 have been found under the skin of persons in tropical America, and a few 

 instances of such cases in the United States. The larvae are thick and broad 

 at one extremity and elongate and tapering at the other. 



The family Syrphidae, Syrphus-flies, flower-flies, or hover-flies, as the 

 English call them, is one of the largest in the order; including fully 2500 

 species in the whole world, of which over 300 are found in this country. 

 For so large a family few generalizations regarding the appearance or 

 habits of the flies can be made. Many of the Syrphus-flies resemble bees 

 and wasps in appearance, and almost all are rather bright and handsome 

 insects. They feed on nectar and pollen, and hence are to be found in sun- 

 shiny hours at flowers, hovering like tiny humming-birds in front of open 



FIG. 478. FIG. 479. 



FIG. 478. A flower-fly, Eristalis tenax. (One and one-half times natural size.) 

 FIG. 479. Diagram of wing of Syrphus contumax, showing venation. 



blossoms, or crawling bee-like in and out of deep flower-cups. Some make 

 a distinct humming or buzzing as they fly about and thus heighten their 

 suggestion of bees. All can be distinguished, after capture, by the so-called 

 false vein of the wings (see Fig. 479). The larvae live variously in decaying 

 wood or other vegetation, or decomposing flesh, or in the stems of green 

 plants, or in toadstools, or in water. Some crawl about, slug-like in manner, 

 over leaves, preying on aphids and scale-insects. Some live as guests in ants' 

 nests, and others in the underground nests of bumble-bees. 



Those Syrphid larvae most often written about are the curious "rat-tailed 

 maggots" (Fig. 480), larvae which live in stagnant water or slime and have 

 the posterior extremity of the body greatly elongate and projecting to serve 

 as a breathing-tube. There is a spiracle (breathing-pore) at the tip of this 

 "tail," and the tail projects upward so that its tip reaches the air, while the 

 rest of the larva's body remains underneath the water. The larvae of Micro- 



