The bluebottle and blow- or flesh-flies are not so numerous in or about human habitations as the house-fly, yet they are not to be considered a minor factor as a carrier of disease. The Lucilia cœsor is the commonest bluebottle or greenbottle fly and is most likely to frequent houses before rain.
Some species breed exclusively on meat, while others may lay their larvæ on meat, open sores, decaying vegetable material, cow manure and undigested human dejecta. The larvaa grow rapidly and attain full size in about five days. They develop into adults in two weeks. The Sarcophaga sarracenœ, which resembles an extra large house-fly, is, perhaps, the most abundant flesh-fly in this country.
The habits, breeding places and nature of these flies make them a tangible factor in the dissemination of typhoid fever. This can best be exemplified by citation of one instance in which such was the case