THE LIVING WORLD. 
256 
healthful but repulsive appetite is thus made to subserve the sanitary inter¬ 
ests of the higher animals. The larval stage is about a fortnight in duration; 
the egg period but twenty-four hours; the pupal age a >veek or two. Exam¬ 
ined under the microscope, the wonders of their mechanism become apparent, 
and one cannot but be struck by the wonderful provision for the life which 
they are to. live. 
The Sheep-Tick and the Bat-Tick have aborted wings—an illustration of 
the economy of natural life, which, except in man, prevents one’s powers from 
wasting because unused, by removing the organs which would serve no useful 
purpose. The fungus gnat ) found under the bark of tfees, when about to be 
transferred into pupa, will form into long processions five inches in breadth, 
and travel in a solid column. This fly is known as the army-worm, and its 
ravages are well known. The blow-fly (Musca vomitoria) is well known to 
housekeepers by its jet-black color, and varied by the steel-blue of the 
abdomen, by its ready perception of the odors of food which is being cooked, 
and by its persistent 
intrusiveness in deposit¬ 
ing in meat or vege¬ 
tables eggs which will 
hatch in a single day. 
The gall-fly is a very 
minute, very delicately 
constructed, and very 
beautiful species. The 
galls so frequently seen 
upon the oak are swell¬ 
ings caused by the in¬ 
sect, which uses them 
as a nest for its eggs, of 
which as many as sixty 
have been found in a 
single gall. Though single species confine themselves to some favorite kind of plant, 
yet among the various species numbers of trees and plants are thus selected, 
and as the insect attacks every part of the plant, from the smallest to 
the thickest root, and from the wood of the root to the most delicate leaf, its 
devastations are to be feared. The buffalo gnat is found in incredible numbers 
in the Southern States, and causes the most serious loss of cattle. Another 
species is found in the Eastern and Middle States, and is called the black- 
fly. Sportsmen in the Adirondacks, for example, suffer great annoyance 
unless they respect the season which this irritating insect appropriates to 
itself, with such annoying results to its victims. 
The Triodite devours the eggs of the locust. The syrfhus vestius is 
half an inch in length, and is marked with yellow bands upon a green 
metallic ground. Its larvae feed upon plant-lice, and thus keep their number 
within some sort of bounds. The stable-fly does not frequent dwellings, 
and as it lives by sucking the blood of vertebrates, its proboscis is slenderer, 
stronger and better adapted for piercing. 
The Tsetse Fly, though deadly to domestic animals, is harmless to- 
men and to wild animals. 
