INTRODUCTION. B sl 
GROUPING OF PARASITIC INSECTS. 
The group of insects taken in its wider sense or as usually given in 
the older text-books (the Tracheata of modern systems) includes all 
those animals having jointed bodies with jointed limbs and breathing 
by means of trachea or respiratory tubes distributed throughout the 
body. 
This main group is divided into four subgroups: The Hexapoda, or 
Insecta proper, including all the six-footed, winged forms; the Arach- 
nida, including the eight-footed forms, none of them winged or provided 
with antenne, and with the body not distinctly separated into head, 
thorax, and abdomen (spiders, mites, ticks, etc.) ; the Myriopoda, having 
elongate bodies and numerous legs (centipedes and millipedes); and 
the Malacopoda, containing a few species of worm-like forms confined 
to tropical latitudes. 
Of these only the two former contain species to be considered in this 
connection, unless, indeed, reference be made to the centipedes, which, 
from their poisonous nature, may at times have an injurious effect on 
man or domestic animals. 
The subgroup Hexapoda is divided into a number of orders, and the 
tendency among recent systematists is to increase the number of these 
orders so that from sixteen to nineteen are recognized in different sys- 
tematic arrangements. Tor the purpose of this work, we may enumerate 
nine groups which may be considered as equivalent in most cases to 
orders, though some of them, notably the Neuroptera and the Pseudo- 
neuroptera, include several of the orders recently established. 
These orders are the Hymenoptera (bees and wasps); the Lepidop- 
tera (butterflies and moths); the Diptera (flies and mosquitoes); the 
Coleoptera (beetles); Hemiptera (bugs and lice); the Orthoptera 
(crickets and grasshoppers); Pseudoneuroptera (dragon flies, May 
flies, etc.); the Neuroptera (shad flies, caddice flies, etc.); the Thy- 
sanura (springtails). 
In the first of these orders, Hymenoptera, no species parasitic on 
domestic animals occurs. Bees and wasps, by virtue of their stings, 
render themselves obnoxious to animals; but since their attacks are 
entirely in the way of self-defense, and never in the form of parasitism, 
and as such attacks are not limited to any species either of insect or 
animal attacked, we deem it unnecessary to make further mention of 
the group. 
Of the Lepidoptera, no species attack the higher animals. The bee 
moths are sometimes very destructive in hives, but these will be found 
treated in works on the apiary. 
The order Diptera includes a number of families containing parasitic 
or semiparasitic species. The members of this order are distinguished 
by having only one pair of wings, the second pair being represented 
by rudiments called halteres, balaucers, poisers, ete. The Culicide 
