Read an Excerpt
A Guide to Familiar American Insects
By Herbert S. Zim, Clarence Cottam, James Gordon Irving, Susan Simon
St. Martin's PressCopyright © 2002 St. Martin's Press
All rights reserved.
Insects have been on this earth for nearly 400 million years and are found nearly everywhere, even in the Antarctic. More kinds of insects are known than all other animals visible to the naked eye. A few insects have been called man's worst enemy, but we would be hard put to exist without them. Insects play many important roles in the environment. They are an important food source for many animals, extraordinary pollinators, and play a critical role in recycling. They are also gems of natural beauty, zoological mysteries, and a constant source of interest.
WHAT INSECTS ARE Insects are related to crabs and lobsters. Like these sea animals, they possess a kind of skeleton on the outside of their bodies. The body itself is composed of three divisions: head, thorax, and abdomen. The thorax has three segments, each with a pair of jointed legs; so an insect normally has six legs. Most insects also have two pairs of wings attached to the thorax, but some have only one pair, and a few have none at all. Insects usually have three sets of mouthparts, two kinds of eyes — simple and compound — and one pair of antennae.
This describes typical insects, but many common ones are not typical. The thorax and abdomen may appear to run together. Immature stages (larvae) of many insects are worm-like, though their six true legs and perhaps some extra false ones may be counted. Immature insects are often difficult to identify. It is also hard to tell the sex of some insects. In some groups males are larger or have larger antennae or different markings. Females are sometimes marked by a pointed ovipositor for laying eggs extending from the base of the abdomen.
INSECT RELATIVES A number of animals are often confused with insects. Spiders, ticks, and mites have only two body divisions and four pairs of legs. They have no antennae. Other insect-like animals have the head and thorax joined like the spiders. Crustaceans have at least five pairs of legs and two pairs of antennae. Most live in water (crabs, lobsters, shrimps), but the sowbug is a land dweller. Centipedes and millipedes have many segments to their bodies with one pair of legs (centipedes) or two pairs (millipedes) on each. Centipedes have a pair of long antennae; millipedes have a short pair.
NUMBER OF INSECTS The insect group (Class Insecta) is by far the largest group of animals in the world. Over a million species have been identified, but one authority estimates this may be only 3 percent of the insects yet to be discovered. The class is divided into over 30 orders. One order encompasses the butterflies and moths; one, the termites; another, the beetles. The beetles alone include some 280,000 described species. There are more kinds of beetles than kinds of all other animals known, outside the insects. Butterflies and moths total over 146,000 species. Bees, wasps, and ants number 115,000; true bugs, 65,000 or more. The student of insect life need never run out of material. Over 15,000 species have been found around New York City alone. You can find a thousand species in your vicinity if you look for small insects as well as large, showy ones.
INSECTS AND PEOPLE Whether certain insects are considered helpful or harmful to people depends as much on us as it does on insects. Our ways of farming and raising animals have provided some insects which might otherwise be rare with conditions enabling them to multiply a thousandfold. Less than 1 percent of insects are considered harmful, but these destroy 10 percent of our crops, causing a loss of billions of dollars annually. Some insects are parasitic on other animals, and some carry diseases.
On the other hand, this would be a sorry world without insects. We would have no apples, grapes, or clover, much less cotton, and fewer oranges and garden vegetables, for these and many other plants depend on insects to pollinate their flowers. And there would be no honey, of course. Some insects aid the process of recycling, a process that is essential to life. Some insects help control others, and all help maintain the vitality of ecosystems.
INSECTS IN NATURE In the broad view, insects play an important natural role, not only in ways that benefit humans but in ways that make our rich plant life and wildlife possible. They are food for many kinds of mammals, birds, amphibians, and fish. Many of our songbirds depend almost entirely on an insect diet. Every fisherman knows how freshwater game fish go after insects. Keep this broad view in mind when people start talking about widespread insect control — something that may become possible with newer chemicals and genetic engineering. Pesticide usage on a large scale is devastating to other species, many of which may be rare. Widespread insect control may also have unexpected consequences, creating more problems than it solves.
CONTROL OF INSECTS There are ways to supplement the natural control of insects by birds and other animals. We encourage those harmless insects that prey on harmful kinds. We can exclude insects with screens, discourage them with repellents, trap them, or poison them. Since there are so many kinds of insects that live and feed in so many different ways, there is no single best method to get rid of them. Yet, with concerted effort some dangerous insects have been wiped out over fairly large areas. A unique example of this was the complete destruction of the Mediterranean fruit fly in Florida, which threatened the citrus crop in 20 counties.
If you have an important insect problem, consult your County Agricultural Extension Agent. Often entomologists (insect specialists) at universities or museums can help, or you can turn to the U.S. Department of Agriculture's Insect Identification Laboratory, Agricultural Research Center West, Beltsville, MD 20705, where experts work on nearly every phase of insect life and control. Many of these organizations also have excellent Web sites.
FAMILY TREE OF INSECTS The ancestor of today's insects was probably a segmented worm-like creature. Roaches and many other insects have been around for as long as 200 million years. Today there are over 30 orders of insects (depending on the classification), including over one million described species. Most of the 12,000 kinds of fossil insects identified so far are similar to living species. The illustration above shows some of the basic relationships among insects.
Insects follow different developmental patterns. In the simplest, the newly hatched insect is like a miniature adult. It grows and molts (sheds its skin) till it reaches adult size. In incomplete metamorphosis an immature nymph hatches, grows, and molts. It develops wings only in the last molt. Complete metamorphosis involves (1) egg, (2) larva, (3) pupa or resting stage, and (4) adult. In all three of the developmental patterns reproductive structures are only present or functional following the final molt.
INSECT STRUCTURE is marked by three body divisions (here), six jointed legs, one pair of antennae, and usually one or two pairs of wings. The outer covering, or exoskeleton, is often hardened. Mouth-parts consist of three separate pairs of structures. Internally, insects have a digestive tract and auxiliary digestive organs. Breathing is done by air tubes spreading internally from openings called spiracles. Circulation is open with many of the internal organs being bathed in the green to yellow fluid called hemalymph. Respiration, digestion, and circulation are shown in the longitudinal section (below) and cross-section (below) of the grasshopper, a typical insect. The nervous system (below) shows the brain, which is divided into three parts. Ganglions serve as nerve centers for nearby parts of the body.
Insect structures show vast variation. Adapted to many environments, insects live successfully in nearly every part of the world. They have digestive systems for all kinds of plant and animal food. They thrive on everything from wood to blood. A few species do not eat at all in the adult stage. Mouth-parts are adapted for chewing, sucking, piercing and sucking, and lapping. Equally interesting adaptations are seen in insect wings, body coverings, and reproductive organs. The typical insect leg (as of a grasshopper) has five parts. Grasshopper hind legs are specialized for jumping. The housefly has pads that enable it to walk up windows or across ceilings. In honeybees, the hind leg has special hairs that carry pollen. In many insects the foreleg is used to groom and clean the antennae and body. Insect structures are fascinating to study under a lens.CHAPTER 2
STUDYING AND COLLECTING INSECTS
Our knowledge of many insects is still so incomplete that a serious amateur can look forward to making important and lasting discoveries.
WHERE TO LOOK Practically everywhere: in fields, gardens, woods, roadsides, beaches, and swamps; under stones, rotted logs, and leaves. Look in flowers, on grass, on animals, too. You'll find insects in the air, in or on water, on and in the ground. Sunny areas often yield greatest insect diversity.
WHEN TO LOOK Insects are most common in late spring and summer, but experienced collectors can find them in all seasons. Many groups of insects are more common at night; remember that when collecting. In winter, concentrate on protected spots, such as under stones or bark, and in water. Watch for insects in egg cases or in their resting stage (pupae).
WHAT TO DO Studying insects is not confined to catching them and mounting them in collections. Raising and housing live insects to study their habits is exciting. Anyone can have an insect zoo in old glass jars. Collect immature insects (larvae), provide them with proper food, and watch them grow. Watch caterpillars shed their skins, spin a cocoon or form a chrysalis, and emerge as a moth or a butterfly. See worm-like larvae become flies or beetles. Raise a colony of ants, bees, or termites. You will learn more from live insects than from dead specimens.
Whatever you do with insects, you will need some understanding of what insects are and how they live. Use this book, then read some of the other books suggested. Most important, go out and look at insects. Catch them if you wish, but watch them first. See how they move, how they feed, and what they do.
COLLECTING INSECTS An insect collection can be valuable for study or reference — if it is used. Using a collection means more than making a collection, though this step must come first. Fortunately, beginners can collect insects with simple, low-cost equipment. Not all insects are chased with a net. Hang an old bedsheet out at night with a light in front of it. Similar traps are described in reference books. Try the easiest methods and places first — at your window screens or near a large neon sign. Just gather the insect harvest there.
EQUIPMENT Any large, wide-mouthed jar will serve for confining and raising insects. Tie some gauze or netting over the top. A light net with a long handle is good for catching insects on the wing. A heavier net is better for "sweeping" through the grass or for catching water insects.
Flat boxes with a layer of heavy corrugated cardboard on the bottom to hold pins are fine for storing specimens. Use a mothball to deter insect pests. Purchase and use insect pins; ordinary ones are too heavy and prone to rusting. Learn the tricks that make mounting neat and attractive. A book for records is essential; so are labels. Later you may want spreading boards, pinning blocks, and other accessories. Collecting and preserving specimens requires patience and skill. Read first and then practice with any insects you may find in your own yard. Skill will come with experience. A well-pinned, fully labeled specimen may retain its value for hundreds of years.
FIELD AND LIFE-HISTORY STUDIES may prove more interesting and exciting than collecting. Instead of learning a little about many insects, learn a lot about a few. Field studies can involve unusual problems on which there is little or no scientific information. How do ants recognize one another? How does temperature affect the flight of butterflies? How much does a caterpillar eat? Can beetles recognize color? Such problems can be investigated in your own yard if you are interested. Many insects are known only in the adult form; few facts are known about the rest of their life cycles. Constant observation of wild specimens, or detailed study of captive ones reared under natural conditions, will yield new and interesting facts.
MAYFLIES AND STONEFLIES are unrelated yet similarly adapted to aquatic environments. The 600 or so species of mayflies have transparent, veined wings and a long, forked tail. The adults are short lived, sometimes living only 12 to 24 hours. The stoneflies include some 500 species. The nymphs, like those of mayflies, live in water and are important food of freshwater fish. Some nymphs of both groups take several years to reach the adult stage. Adult stoneflies have transparent wings, though they are not strong fliers.
DRAGONFLIES AND DAMSELFLIES are often seen near rivers, streams, bogs, ponds, and moist meadows, but some species dwell in forests. Dragonflies, also known as darning needles or stingers, hunt small insects like mosquitoes, which they eat on the wing. It is believed that a single large dragonfly eats dozens of mosquitoes every evening. Dragonflies rest with wings outstretched. The more delicate damselfly rests with wings folded. Both lay eggs in water; the nymphs develop there, feeding on other aquatic insects. They leave the water after several growing stages; the skin splits and the adult emerges.
WALKINGSTICKS are large, usually wingless insects with legs all about the same length and shape, distinguishing them from the mantises. Walkingsticks live and feed on leaves of oak, locust, cherry, walnut, and other woody plants, occasionally causing damage. The female's 100 or so eggs are dropped singly to the ground to hatch the following spring. As the young grow, they molt or shed their skin five or six times; otherwise they are similar to adults. Males are smaller than females.
MOLE AND CAMEL CRICKETS These nocturnal crickets live under rocks in moist places, or mostly underground. The large mole cricket burrows near the surface, eating young roots and killing seedlings. In the South, it may destroy peanuts, strawberries, and other garden crops. The pale brown, spotted, wingless camel cricket is identified by its high, arched back. Though scavengers, they often become nuisances around greenhouses.
GRASSHOPPERS AND LOCUSTS All have short antennae and large hearing organs on the sides of the abdominal base. When disturbed, some regurgitate a noxious droplet ("tobacco juice") that discourages many would-be predators. Most are good fliers, though some are wingless. Locusts are merely grasshoppers that migrate, with two distinct phases: solitary and migratory. The latter are more brightly colored and highly gregarious. Females lay 20 to 100 eggs in the ground or in rotted wood. See here for the life history of one species. Nymphs mature in 2 to 3 months.
Excerpted from Insects by Herbert S. Zim, Clarence Cottam, James Gordon Irving, Susan Simon. Copyright © 2002 St. Martin's Press. Excerpted by permission of St. Martin's Press.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.