LESSON 1
ARTHROPOD BIOLOGY AND LIFE CYCLES
Section I. INTRODUCTION
1-1.
GENERAL
a. Ask the average person what an arthropod is and he probably wiII not be able
to tell you. Then ask the same person what an insect is, and he 'wiII probably name
such animals as flies, bees, spiders, chiggers, ticks, mosquitoes, centipedes, scorpions,
etc. He wiII probably be astounded when you tell him that all of the animals that he has
named are not insects but that all are arthropods.
b. War, floods, fire, and famine have all taken their toll on mankind, but the
greatest decimator of all has been disease. Of these diseases, the worst have been
arthropod-borne diseases. Everybody has heard of the infamous plague or "black
death" that swept Europe in the 14th century. Millions died. In fact, one fourth of the
population of Europe perished. That form of plague was arthropod-borne (transmitted
by the rat flea). Nonetheless, horrible as it was, the "black death" was not the most
severe arthropod-borne disease. Malaria, which is transmitted by the Anopheles
mosquito, has killed more people throughout the world than any other communicable
disease.
c. Some arthropod-borne diseases that have affected US soldiers are: yellow
fever, African trypanosomiasis, viral encephalitides, malaria, typhus, Rocky Mountain
spotted fever, and viral hemorrhagic fever. Because of our military commitment to
'other nations, US soldiers are often rushed to other parts of the globe and quickly
exposed to disease-carrying arthropods. These diseases are usually endemic; that is,
they exist at a low level among the local populace at all times. Because local personnel
have been exposed to these diseases all of their Iives, they have buiIt up a natural
tolerance or immunity to these diseases. The American soldier, lacking an immunity,
can quickly become a victim of an arthropod-borne disease.
d. It must be emphasized, however, that the vast majority of arthropods are not
enemies of humans. Some arthropods, such as the honeybee, are essential to our
existence, as efficient pollinators of fruit trees, clover, vegetable crops, and other useful
plants. Insect products such as siIk, honey, beeswax, and lac (the basic material for
shellac) are products we use. Many insect species are essential to human welfare
because of their part in combating other species that are harmful, thus maintaining a
biological balance in nature. Some serve as predators, feeding upon harmful four
insects and plants and keeping them under control. Others are parasites of harmful
pests and are used in various biological control situations.
MD0170
1-2