The rat (mus rattus), too, perhaps, may be united with these companions of mankind. Not knowing it in an independent state, we cannot say what its resources might be, but so sagacious and powerfully endowed an animal could always provide for its own necessities; yet it prefers our provision to any precarious supply from its own industry. In summer it partially quits our dwellings, the heat and dryness of our buildings becoming irksome to it, and the occasional difficulty of obtaining water, in which it delights, prompts it to resort to hedges and banks for a certain period; but it always returns when our barns are filled, and ready for it. The house fly (musca carnaria)[50] is another creature that appears domesticated with us; in some seasons a very numerous, and always a very dirty inmate. It associates in our windows at times with a similar insect (stomoxys calcitrans), that loves to bask on stones and posts, and which is now biting my legs with the most teasing perseverance. But this phlebotomist has not the same attachment to our habitations, is a more solitary insect, and does not unite in those little social parties, that circle for hours in a sober uniformity of flight below the ceilings of our chambers. Wherever man appears, this house fly is generally to be seen too: and instances are known, when islands have been taken possession of very far removed from the main land, that for a time no flies were visible, yet ere long these little domestic insects have made their appearance; neither natives of the isle, nor can we reasonably suppose them to have taken flight from a distant shore; but probably the offspring of parents that came with the stores in the vessel of the party.