Until very recent years insects and their allies have been considered as
of economic importance merely in so far as they are an annoyance or
direct menace to man, or his flocks and herds, or are injurious to his
crops. It is only within the past fifteen years that there has sprung
into prominence the knowledge that in another and much more insiduous
manner, they may be the enemy of mankind, that they may be among the
most important of the disseminators of disease.