2 Insect Life : Its Why and Wherefore 
house fly is “ Musca domestica,” a medium 
sized greyish fly, the mouth-piece of which 
consists of a trunk or proboscis, terminated 
by a sucker, composed of two tubes, by 
which it is enabled to suck up fluid sub- 
stances. This proboscis is capable of being 
entirely withdrawn within the cavity of 
the mouth, when the insect is not feeding. 
This tongue, from its formation, is in- 
capable of penetrating the skin, though 
provided with a terminal framework of 
tracheal tubes which, acting like a rasp, 
enable the insect to worry us with a 
tickling sensation, but it is quite unable 
to bite. 
There is another fly which is very fond 
of entering our houses, and which, none, 
probably, but an expert, would detect as 
differing from the house fly in appearance. 
This gentleman possesses the name of 
“ Stomoxys Calcitrans,” but from a point 
of view other than his mere exterior he 
differs very materially from the “ Musca 
domestica ” in that his mouth parts are 
formed for the very purpose of piercing the 
skin. Just as the house fly is common to 
nearly every part of the world, so his 
