LIBRARY

204 COLLEGE ENTOMOLOGY
of the world and are now cosmopolitan. They are certainly as old as the human
race and older than its domesticated animals.
The life history of most species is rather simple. Because of the uniformity
of the body temperatures of the hosts, living conditions are fairly uniform
throughout the year, and the most striking variations occur between tropical
and polar climates and outdoor and indoor conditions during winters in the
temperate and colder ranges of the hosts.
Sanitation of the body and living quarters have much to do with the abundance
of these insects on man and on his domestic animals.
The most important hosts are:
Order PRIMATES: apes, man, monkeys.
Order UNGULATA (hoofed mammals): domesticated animals: cattle,
goats, horses, sheep, elephants; wild animals: buffaloes, deer, sheep, elephants,
zebras.
Order RODENTIA (rodents); domestic and wild: chipmunks, marmots,
mice, prairie dogs, rabbits, hares, rats, squirrels, woodchucks.
Order CARNIVORA (carnivores, domestic ·and wild): land animals: dogs;
marine animals: seals, sea elephants, sea leopards, sea lions, walruses.
Important animals immune from or only rarely infested by sucking lice:
Order MARSUPIALIA: kangaroos, wallabies, wombats, phalangers, opossums.
Order EDENTATA: sloths, anteaters, armadillos.
Order CARNIVORA, Family FELIDlE: cats, cougars, jaguars, leopards,
lions, lynxes, tigers.
Order INSECTIVORA: cobegos, moles, shrews, tenrecs.
There are no marked changes in the development of an individual, but there
are normally four instars during its life history. The eggs or nits are simple
and oval or elongated without definite surface markings. The most remarkable
thing about them is the manner in which some are attached to the hairs and
wool of the hosts. They are arranged singly or in groups, usually near the skin
of the host, and hatch in from a few days to a week or more. The young greatly
resemble the adults but are usually paler in color. AU living forms are rather
slow, but move with sufficient speed and skill among the hairs and in clothing
to give rise to the old saying: "You can't catch a louse with one finger." Reproduction
occurs throughout the year, uninterrupted in the tropics and only
slowed up during the winters in the colder regions. Under certain conditions
in the health and physical state of the hosts, in the sanitation of their surroundings,
and under favorable climatic environmental factors, some species of
lice become so abundant as to injure the host greatly or destroy it completely.
They either perish with the host or leave the cold body to seek other living
animals. Thus the destruction of the host often means the dispersal of or the
complete extinction of the lice. The actual presence and the effects of these
insects on the host are known as pediculosis. The species infesting man carry
and transmit certain serious and often fatal diseases such as typhus fever,
trench fever, and relapsing fever, especially in concentration camps of refugees,