the hands of those they torment they soon die victims to their
sanguinary appetite."

CHAPTER IV

HOW INSECTS CAUSE OR CARRY DISEASE

It has been estimated that there are about four thousand species or
kinds of Protozoans, about twenty-five thousand species of Mollusks,
about ten thousand species of birds, about three thousand five hundred
species of mammals, and from two hundred thousand to one million species
of insects, or from two to five times as many kinds of insects as all
other animals combined.

Not only do the insects preponderate in number of species, but the
number of individuals belonging to many of the species is absolutely
beyond our comprehension. Try to count the number of little green aphis
on a single infested rose-bush, or on a cabbage plant; guess at the
number of mosquitoes issuing each day from a good breeding-pond;
estimate the number of scale insects on a single square inch of a tree
badly infested with San Jose scale; then try to think how many more
bushes or trees or ponds may be breeding their millions just as these
and you will only begin to comprehend the meaning of this statement.

As long as these myriads of insects keep in what we are pleased to call
their proper place we care not for their numbers and think little of
them except as some student points out some wonderful thing about their
structure, life-history or adaptations. But since the dawn of history we
find accounts to show that insects have not always kept to their proper
sphere but have insisted at various times and in various ways in
interfering with man's plans and wishes, and on account of their
excessive numbers the results have often been most disastrous.

Insects cause an annual loss to the people of the United States of over
$1,000,000,000. Grain fields are devastated; orchards and gardens are
destroyed or seriously affected; forests are made waste places and in
scores of other ways these little pests which do not keep in their
proper places are exacting this tremendous tax from our people.

These things have been known and recognized for centuries, and scores of
volumes have been written about the insects and their ways and of
methods of combating them.

But it is only in recent years that we have begun to realize the really
important part that insects play in relation to the health of the people
with whom they are associated. Dr. Howard estimates that the annual
death rate in the United States fro