Whereas the blue-bottle rarely enters the dwellings of mankind, except gravid females led by the sense of smell in search of fish, or flesh meat, and (less eagerly) sweets, both species of house-fly and _both sexes_ seem to delight in the mere odour of humanity; breeding females will seek the larder and the dust-bin, but others will very provokingly pervade all quarters. Although avoiding a dark or deeply shaded room, the house-fly seems to like partial shade; it will be content to remain indoors and to rejoice in a warm kitchen, even on a hot summer's day, whilst all the other kinds of flies are enjoying the outdoor sunshine. It may be said of nearly a dozen other species, occasionally observable crawling on window panes, that they are "outdoor" flies, and that their occurrence indoors is accidental. In fact, they are mostly observed when trying to escape. Next after human habitations, stables, cow-sheds and pig-sties are the delight of the breeding female house-fly. Round about and in these latter resorts she associates with an immense host of rather small sized flies, and amongst a few others of equal size with the skin-piercing and blood-sucking stable-fly; but many stablemen are ignorant of the difference of the two kinds of flies and of the serious suffering of their horses from the bites of the stable-fly. This lamentable ignorance was shared by the joint authors of "Humble Creatures," published in 1858, when Neo-Darwinism was in vogue, and many books were published for popularising a knowledge of common things and spreading an interest in nature-study; this publication, which is still (1914) in print and very little revised, has probably led some later would-be nature-study teachers to follow suit in confusing the characteristics of the two species. Very often the fly most numerously breeding in the manure heaps of the mews will be _Borborus equinus_, or some other of the same family, which are characterised by a very simple pattern of wing nervures and by the absence of squamæ or scales behind the wings; also the ankle joints of the feet are most peculiarly short and broad. _B. equinus_, and a great host of other dung breeding flies of a still smaller size, may be considered beneficial insects; they do not pester cattle, and their larvæ make food more scarce for injurious flies. The breeding habits of the blue-bottle are very conspicuous by reason of its haste and boldness in taking possession of dead animals. It is incapable of breeding in horse or cow dung, to which latter the green-bottle fly often resorts.