The various species of flies which are commonly annoying about habitations or where foodstuffs are being prepared may be divided roughly into two classes: (1) Those which breed in animal matter, consisting mainly of the so-called blowflies, including the screw-worm fly;[1] and (2) those which breed in vegetable as well as in animal matter. In the latter group the house fly[2] is by far the most important. The stable fly is strictly a vegetable breeder, as are also certain other species which occasionally come into houses and in rare cases may contaminate foodstuffs. The stable fly,[3] which breeds in cow manure or decaying vegetable matter, and the horn fly,[4] which breeds in manure, are blood-sucking species, and can be caught in ordinary flytraps in comparatively small numbers only. The kind of flies caught depends to a considerable extent on the material used for bait. In general the house fly and other species which breed in vegetable matter are attracted to vegetable substances, while the blowflies will come most readily to animal matter. This rule, of course, is not absolute, as flies are less restricted in feeding than in breeding habits, and, as is well known, the house fly is attracted to a greater or less extent to any moist material, especially if it has an odor.