ring in the methods adopted to prevent the spread of yellow fever.
There are no striking characters or habits in the larval or pupal stages
that would enable us to distinguish without careful examination this
species from other similar forms with which it might be associated. For
some time it was claimed that this species would breed only in clean
water, but it has been found that it is not nearly so particular, some
even claiming that it prefers foul water. I have seen them breeding in
countless thousands in company with _Stegomyia scutellaris_ and _Culex
fatigans_ in the sewer drains in Tahiti in the streets of Papeete. As
the larvae feed largely on bacteria one would expect to find them in
exactly such places where the bacteria are of course abundant.

The fact that they are able to live in any kind of water and in a very
small amount of it well adapts them to their habits of living about
dwellings.

So far as known the members of these two genera are the only two that
are concerned in the transmission of disease in the United States. In
other countries other species are suspected or proven disseminators of
certain diseases, but these will be discussed in connection with the
particular diseases in later chapters.

OTHER SPECIES

The many other species of mosquitoes that we have may be conveniently
divided as to their breeding-habits into the fresh-water and the
brackish-water forms. Among the fresh-water kinds some are found
principally associated with man and his dwelling places, others live in
the woods or other places and so are far less troublesome. Most of
these do not fly far. Several of the species that breed in brackish
water are great travelers and may fly inland for several miles. Thus the
towns situated from one to three or four miles inland from the lower
reaches of San Francisco Bay are often annoyed more by the mosquitoes
that breed only in the brackish water on the salt marshes than they are
by any of the fresh-water forms (Figs. 86, 87). The worst mosquito pest
along the coast of the eastern United States and for some distance
inland is a species that breeds in the salt marshes.

NATURAL ENEMIES OF MOSQUITOES

In combating noxious insects we learned long ago that often the most
efficient, the easiest and cheapest way is to depend on their natural
enemies to hold them in check. Under normal or rather natural conditions
we find that they are usually kept within reasonable bounds by their
natu