If any readers of this booklet are disposed to join and form a central body with a view of ultimately founding an association for promoting the work of fly extermination, the writer will be glad to find or meet with an honorary secretary and helpers who will work in the cause and economise in the necessary expenditure of all contributions received. After the preliminary efforts of starting such an association, its work will be not only to urge the local sanitary authorities everywhere to adopt the best possible course of action, but also to incessantly move public opinion to compel Parliament to pass laws, capable of administration, for the public welfare in this matter. The present booklet had its origin very many years ago in the author's idea of writing an account of the house-fly and its kindred, which would be interesting and more truthful than much then to be found in current literature. Such off-hand inconsiderate writing, as appears in the "Elements of Entomology," by W. S. Dallas, F.L.S., requires to be controverted; therein it is stated that the house-fly, which is "troublesome, does very little actual damage, for our only real grounds of complaint are to be summed up in the tickling sensation which its feet cause," &c. "In its larvæ state, however, it lives inoffensively enough in dung." It has now seemed timely to publish my long-delayed work, re-written with the object of more urgently interesting the general public in the cause of the anti-fly campaign. Still, the author trusts that both the deeper and the less entomologically inclined nature students will find therein not only useful, but also some novel information, given with not too much entomological technicality.