Kingdom: Anamalia Subkingdom: Bilateria Phylum: Arthropoda Subphylum: Uniramia Class: Insecta
Orders: Common orders include Coleoptera (beetles); Diptera (flies, mosquitoes); Hemiptera (true bugs); Homoptera (cicadas), Hymen-optera (ants, bees, wasps); Isoptera (termites); Lepidoptera (butterflies, moths); Odonata (dragonflies, damselflies); Orthoptera (crickets, grasshoppers) Geographical location: Every continent except Antarctica Habitat: Mainly terrestrial, some aquatic, primarily freshwater Gestational period: Highly variable; some insects produce one, two, or several generations per year; conversely, relatively large insects may take more than one year for larval development Life span: Highly variable; adult mayflies live less than one week, while queen termites have been known to live for more than twenty years
Special anatomy: Major regions include the head, featuring one pair of antennae, the thorax, with three pairs of legs and up to two pairs of wings, and the abdomen, housing spiracles and genitalia; in some insects, one or both pairs of wings are modified for functions other than flight, such as protection or balance
Image Not Available examples of raptorial modifications for grasping and holding struggling prey.
Dragonfly nymphs, the young aquatic stage, have a diet of insects, crustaceans, tadpoles, and even small fish. Adult dragonflies eat bees, butterflies, and mosquitoes. Harmless insects such as dragonflies, which consume pest insects such as mosquitoes, are good candidates for biological control programs. Biological control is a method of pest control that takes advantage of natural predators of the pest. Ladybugs are commonly used by gardeners to control plant-damaging aphid populations.
On the other hand, a good parasite does not kill its food source, the host. Parasitic insects typically ingest host blood, mucus, or tissues, with minimal irritation or harm to the host. Trouble begins if there is a heavy parasitic burden (a large number of parasites per host), or if the parasitic insect transmits disease-causing organisms to the host. Ectoparasites live on the outside of their hosts. In this category, fleas and lice are adapted to avoid detection by the host and deter removal during normal grooming processes. Endoparasitic fly larvae live in the digestive or respiratory tract, mainly of livestock. Endoparasites of invertebrates do not follow the rules. Because there is little difference in size between this parasite and host pair, the host routinely perishes in this relationship. Species of endoparasitic wasps inject their eggs into caterpillars. When the larvae hatch, they tunnel farther into the host and feed off of its tissues. Upon completion of larval development, the wasps emerge from the caterpillar, killing it in the process.
Some parasites spend their lifetimes closely associated with the host, but others only briefly visit the host. On the time continuum, lice not only form a constant, more-or-less permanent associa tion with a single host, but many generations of lice may inhabit the same host. However, these parasites are transferred from host to host during mating, nesting, or other close contact between individuals. Unlike lice, fleas leave the host frequently between bloodmeals. On the other end of the spectrum, mosquitoes normally require multiple hosts to complete a single bloodmeal; they are here and gone before they can be slapped by hand or tail.
Much of what insects do, they do by instinct, a genetically preprogrammed response to environmental stimuli, none the less amazing in its elegance and effectiveness. Antennae and setae, hairlike projections through the exoskeleton, serve as two of the many receptors of external stimuli. The necessity of keeping these sensory organs clean is evidenced by preening, commonly using mouthparts and legs. Major categories of environmental stimuli signal friend or foe.
Many insects locate opposite sex conspecifics, individuals of the same species, by sight. Color patterns, especially in the ultraviolet (UV) spectrum attract potential mates. Fireflies (Coleoptera) use visual recognition of patterns of light flashes. In some species, females use signaling to attract males. In other species the male and female signal to each other with the proper code and response. Females of the genus Photuris mimic the flashing patterns of other firefly species. When the male approaches, she makes a meal of him.
Sound production and reception are also used for mate location. The sound generated by a female mosquito's beating wings in flight is picked up by the male mosquito's antennae. Male ho-mopterans and orthopterans produce songs of courtship. Cicadas use abdominal muscles and a resonating chamber for sound production. Grasshoppers and crickets rub their wings and or legs together. Sound receptors, "eardrums" of females in these orders, are found on their forelegs or first abdominal segments. Sound production and reception vary with temperature.
Pheromones, externally broadcast chemical signals, are another means of attracting mates. In moths, glands near the tip of the female's abdo-
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