Why flies are both a nuisance and a menace to health scarcely needs any longer to be explained. The smallest schoolboy has been taught to look on these little insects as enemies that must be conquered. Something more than flytraps and flypaper and screens are requisite for a successful campaign. We may continue to "swat the fly" with unabated vigor for years to come; but until the life habits and reproductive phenomena of this species are clearly understood so that scientifically founded plans for the conquest of the objectionable creatures can be put into operation, progress will scarcely be demonstrable. Sanitary and medical projects have need of the entomologist in this as in various other modern problems that bear on animal welfare or human health and comfort.
Of flies it is well known that they are attracted by most forms of food and putrid substances, and that they breed where