The Two-winged Flies 
339 
Fee, 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 continuax , 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- 
