It has already been explained that the scavenging service of the house-fly can be altogether dispensed with, inasmuch as there is a sufficiency of other less noxious flies and creatures devoted to such work. Reflecting on the Story of Creation, and the mission of man as first a gardener, and then, when expelled from Paradise, destined to more laboriously cultivate the earth, it may be held to be man's allotted duty not only to wage war against weeds, but likewise to distinguish friends and foes of all kinds, and treat accordingly creatures even of all branches of the animal kingdom, whether insects, reptiles, birds, or mammals, favouring one and exterminating another. This will be to rule the earth and "subdue it" (Genesis i. 28). Nemesis will inevitably chastise man unless he rectifies the consequences of his own delinquencies, whether they be direct or indirect. The "good service" of the house-fly is comparable with that of the flea, which performs an unwelcomed and indirect "service," inciting the housewife to have well-swept floors and clean bedding. The unalloyed good service of insectivorous flies is quite apparent. The details of their life-history and a description of their different characteristics would make an interesting volume, but the limitations of the present work preclude such enlargement of its scope. It certainly stands to the credit of the blue-bottle that she is by far our best native scavenger of carrion; so good, indeed, that none other as an assistant is needed. She may just possibly sometimes convey germs and contaminate food, but she does not so directly assail man. Her larger size makes her easy for exclusion from the domestic food store. So eager and alert is the female in searching for meat, dead animals, and fish, that our other native carrion-feeding flies are at a great disadvantage in the struggle for existence; so prompt is she in monopolising carrion, that would-be competitors often have to be content with laying their eggs in less rich food materials. The blue-bottle can withstand temperatures a few degrees colder than can those flies to which she is nearest akin; and she seems capable somehow of sheltering herself better. Even as late as the middle of winter, sometimes, a dead bird may be found to be fly-blown under circumstances which indicate that the eggs must have been laid in frosty weather, when flies are not seen at large. The explanation is that the blue-bottle will for a short time awake, and venture outside her retreat in a sheltered south wall, warmed by a few hours of winter sun. She does not hibernate in early winter in such a continuous state of rigid torpor as, for instance, does the queen wasp; probably few or none survive the winter by a real hibernation, the progenitors of the first spring broods emerging at a date no earlier than do their rivals and congeners.