dogs, horses, hogs, cattle, and many species of wild animals. Humans also may be 
bitten, but they are not a preferred host (777). Unfed adults are brown, variously 
marked with white, and about 5 mm long. Engorged females are bluish gray and 
sometimes reach a length of 12 mm. Females lay eggs in various places but never 
on the host; the young seek out their host after hatching. Heaviest infestations are 
usually found on vegetation along game trails, paths, and roadways. Adults are 
most abundant during spring and early summer in the North. After August they are 
usually very scarce. In the South, they occur throughout the year. This species 
transmits Rocky Mountain spotted fever and tularemia, both serious diseases of 
humans. It also transmits anaplasmosis, a disease of cattle. 
The blacklegged tick, /xodes scapularis Say, occurs along the Atlantic Coast. 
The larvae and nymphs feed on rodents and reptiles, and the adults feed on deer, 
cattle, sheep, dogs, and other large animals. People are also bitten. This species has 
long mouth parts and inflicts a very painful bite. Infestations are usually found on 
vegetation along game trails, paths, and roadways where people and other animals 
come by. Adult ticks are most prevalent during fall and early winter. This species 
transmits anaplasmosis to cattle and piroplasmosis to dogs (/2/9). 
Class Insecta—Insects 
An insect is an air-breathing arthropod with a distinct head, thorax, and ab- 
domen. It has one pair of antennae, three pairs of legs, and usually one or two pairs 
of wings in the adult state. The majority of species are terrestrial and are found in an 
almost endless variety of microhabitats on the land. Many other species spend part 
of their lives in water. 
The majority of insects hatch into wormlike larvae that grow by periodically 
shedding the outer skin, finally transforming into an inactive pupal stage from 
which the adult emerges. This type of development is known as complete meta- 
morphosis. The immature stages of some others are very similar in appearance to 
the adults and are known as nymphs. Members of the latter group are said to have 
simple or incomplete metamorphosis. 
Approximately 900,000 species of insects have been described. These species 
represent 80 to 90 percent of all the known kinds of animals. The actual number of 
insect species, however, 1s believed to be much larger and to run into the millions 
(1048). Countless numbers feed on plants of all kinds, attacking all parts from the 
roots in the ground to the flowers and seeds in the tops. Thousands of others feed on 
other insects or other animals, including people. 
Fortunately for humans and their interests, the majority of insects are either 
innocuous or beneficial. The remainder, unfortunately, include some of our most 
important enemies—not only do they feed on humans and other animals and often 
transmit deadly or debilitating disease organisms, but they also devour crops and 
decimate forests. Because of their abundance, their fantastic reproductive powers, 
and their remarkable capacities for adapting to changing conditions, insects present 
a continuing challenge to us in our efforts to limit their numbers to tolerable levels. 
Several general references to insects are available for consultation (/40, /55, 
LOD" 23083605025, 725% 828, 1043). 
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