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Readers receive an overview of insect life — metamorphosis, digestion, reproduction, and other areas — as well as particulars of dozens of different species. Subjects include grasshoppers and their relatives, roaches and other ancient insects, termites, plant lice, cicadas, caterpillars, moths, mosquitoes, and flies. In addition to its value as a reference, this study and its first-rate illustrations provide a splendid source of browsing for professionals and amateurs alike.
Product Details
| ISBN-13: | 9780486806273 |
|---|---|
| Publisher: | Dover Publications |
| Publication date: | 06/15/2015 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 416 |
| File size: | 26 MB |
| Note: | This product may take a few minutes to download. |
About the Author
Read an Excerpt
Insects
Their Ways and Means of Living
By Robert Evans Snodgrass
Dover Publications, Inc.
Copyright © 2015 Robert Evans SnodgrassAll rights reserved.
ISBN: 978-0-486-80627-3
CHAPTER 1
THE GRASSHOPPER
Sometime in spring, earlier or later according to the latitude or the season, the fields, the lawns, the gardens, suddenly are teeming with young grasshoppers. Comical little fellows are they, with big heads, no wings, and strong hind legs (Fig. 1). They feed on the fresh herbage and hop lightly here and there, as if their existence in no way involved the mystery of life nor raised any questions as to why they are here, how they came to be here, and whence they came. Of these questions, the last is the only one to which at present we can give a definite answer.
If we should search the ground closely at this season, it might be possible to see that the infant and apparently motherless grasshoppers are delivered into the visible world from the earth itself. With this information, a nature student of ancient times would have been satisfied — grasshoppers, he would then announce, are bred spontaneously from matter in the earth; the public would believe him, and thereafter would countenance no contrary opinion. There came a time in history, however, when some naturalist succeeded in overthrowing this idea and established in its place the dictum that every life comes from an egg. This being still our creed, we must look for the grasshopper's egg.
The entomologist who plans to investigate the lives of grasshoppers finds it easier to begin his studies the year before; instead of sifting the earth to find the eggs from which the young insects are hatched in the spring, he observes the mature insects in the fall and secures a supply of eggs freshly laid by the females, either in the field or in cages properly equipped for them. In the laboratory then he can closely watch the hatching and observe with accuracy the details of the emergence. So, let us reverse the calendar and take note of what the mature grasshoppers of last season's crop are doing in August and September.
First, however, it is necessary to know just what insect is a grasshopper, or what insect we designate by the name; for, unfortunately, names do not always signify the same thing in different countries, nor is the same name always applied to the same thing in different parts of the same country. It happens to be thus with the term "grasshopper." In most other countries they call grasshoppers "locusts," or rather, the truth is that we in the United States call locusts "grasshoppers," for we must, of course, concede priority to Old World usage. When you read of a "plague of locusts," therefore, you must understand "grasshoppers." But a swarm of "seventeen-year locusts" means quite another insect, neither locust nor grasshopper — correctly, a cicada. All this mix-up of names and many other misfits in our popular natural history parlance we can blame probably on the early settlers of our States, who bestowed upon the creatures encountered in the New World the names of animals familiar at home; but, having no zoologists along for their guidance, they made many errors of identification. Scientists have sought to establish a better state of nomenclatural affairs by creating a set of international names for all living things, but since their names are in Latin, or Latinized Greek, they are seldom practicable for everyday purposes.
Knowing now that a grasshopper is a locust, it only needs to be said that a true locust is any grasshopperlike insect with short horns, or antennae (see Frontispiece). A similar insect with long slender antennae is either a katydid (Figs. 23, 24), or a member of the cricket family (Fig. 39). If you will collect and examine a few specimens of locusts, which we will proceed to call grasshoppers, you may observe that some have the rear end of the body smoothly rounded and that others have the body ending in four horny prongs. The second kind are females (Fig. 2 B); the others (A) are males and may be disregarded for the present. It is one of the provisions of nature that whatever any creature is compelled by its instinct to do, for the doing of that thing it is provided with appropriate tools. Its tools, however, unless it is a human animal, are always parts of its body, or of its jaws or its legs. The set of prongs at the end of the body of the female grasshopper constitutes a digging tool, an instrument by means of which the insect makes a hole in the ground wherein she deposits her eggs. Entomologists call the organ an ovipositor, or egg-placer. Figure 2 B shows the general form of a grasshopper's ovipositor; the prongs are short and thick, the points of the upper pair are curved upward, those of the lower bent downward.
When the female grasshopper is ready to deposit a batch of eggs, she selects a suitable spot, which is almost any place in an open sunny field where her ovipositor can penetrate the soil, and there she inserts the tip of her organ with the prongs tightly closed. When the latter are well within the ground, they are probably spread apart so as to compress the earth outward, for the drilling process brings no detritus to the surface, and gradually the end of the insect's body sinks deeper and deeper, until a considerable length of it is buried in the ground (Fig. 3).
Now all is ready for the discharge of the eggs. The exit duct from the tubes of the ovary, which are filled with eggs already ripe, opens just below and between the bases of the lower prongs of the ovipositor, so that, when the upper and lower prongs are separated, the eggs escape from the passage between them. While the eggs are being placed in the bottom of the well, a frothy glue-like substance from the body of the insect is discharged over them. This substance hardens about the eggs as it dries, but not in a solid mass, for its frothy nature leaves it full of cavities, like a sponge, and affords the eggs, and the young grasshoppers when they hatch, an abundance of space for air. To the outside of the covering substance, while it is fresh and sticky, particles of earth adhere and make a finely granular coating over the mass, which, when hardened, looks like a small pod or capsule that has been molded into the shape of the cavity containing it (Fig. 4). The number of eggs within each pod varies greatly, some pods containing only half a dozen eggs, and others as many as one hundred and fifty. Each female also deposits several batches of eggs, each lot in a separate burrow and pod, before her egg supply is exhausted. Some species arrange the eggs regularly in the pods, while others cram them in haphazard.
The egg of a grasshopper is elongate-oval in shape (Fig. 5), those of ordinary-sized grasshoppers being about three-sixteenths of an inch in length, or a little longer. The ends of the eggs are rounded or bluntly pointed, and the lower extremity (the egg being generally placed on end) appears to have a small cap over it. One side of the egg is always more curved than the opposite side, which may be almost straight. The surface is smooth and lustrous to the naked eye, but under the microscope it is seen to be marked off by slightly raised lines into many small polygonal areas.
Within each egg is the germ that is to produce a new grasshopper. This germ, the living matter of the egg, is but a minute fraction of the entire egg contents, for the bulk of the latter consists of a nutrient substance, called yolk, the purpose of which is to nourish the embryo as it develops. The tiny germ contains in some form, that even the strongest microscope will not reveal, the properties which will determine every detail of structure in the future grasshopper, except such as may be caused by external circumstances. It would be highly interesting to follow the course of the development of the embryo insect within the egg, and most of the important facts about it are known; but the story would be entirely too long to be given here, though a few things about the grasshopper's development should be noted.
The egg germ begins its development as soon as the eggs are laid in the fall. In temperate or northern latitudes, however, low temperatures soon intervene, and development is thereby checked until the return of warmth in the spring — or until some entomologist takes the eggs into an artificially heated laboratory. The eggs of some species of grasshoppers, if brought indoors before the advent of freezing weather and kept in a warm place, will proceed with their development, and young grasshoppers will emerge from them in about six weeks. On the other hand, the eggs of certain species, when thus treated, will not hatch at all; the embryos within them reach a certain stage of development and there they stop, and most of them never will resume their growth unless they are subjected to a freezing temperature! But, after a thorough chilling, the young grasshoppers will come out, even in January, if the eggs are then transferred to a warm place.
To refuse to complete its development until frozen and then warmed seems like a preposterous bit of inconsistency on the part of an insect embryo; but the embryos of many kinds of insects besides the grasshopper have this same habit from which they will not depart, and so we must conclude that it is not a whim but a useful physiological property with which they are endowed. The special deity of nature delegated to look after living creatures knows well that Boreas sometimes oversleeps and that an egg laid in the fall, if it depended entirely on warmth for its development, might hatch that same season if mild weather should continue. And then, what chance would the poor fledgling have when a delayed winter comes upon it? None at all, of course, and the whole scheme for perpetuation of the species would be upset. But, if it is so arranged that development within the egg can reach completion only after the chilling effect of freezing weather, the emergence of the young insect will be deferred until the return of warmth in the spring, and thus the species will have a guarantee that its members will not be cut down by unseasonable hatching. There are, however, species not thus insured, and these do suffer losses from fall hatching every time winter makes a late arrival. Eggs laid in the spring are designed to hatch the same season, and the eggs of species that live in warm climates never require freezing for their development.
The tough shell of the grasshopper's egg is composed of two distinct coats, an outer, thicker, opaque one of a pale brown color, and an inner one which is thin and transparent. Just before hatching, the outer coat splits open in an irregular break over the upper end of the egg, and usually half or two-thirds of the way down the flat side. This outer coat can easily be removed artificially, and the inner coat then appears as a glistening capsule, through the semitransparent walls of which the little grasshopper inside can be seen, its members all tightly folded beneath its body. When the hatching takes place normally, however, both layers of the eggshell are split, and the young grasshopper emerges by slowly making its way out of the cleft (Fig. 6).
Newly-hatched grasshoppers that have come out of eggs which some meddlesome investigator has removed from their pods for observation very soon proceed to shed an outer skin from their bodies. This skin, which is already loosened at the time of hatching, appears now as a rather tightly fitting garment that cramps the soft legs and feet of the delicate creature within it. The latter, however, after a few forward heaves of the body, accompanied by expansions of two swellings on the back of the neck (Fig. 6), succeeds in splitting the skin over the neck and the back of the head, and the pellicle then rapidly shrinks and slides down over the body. The insect, thus first exposed, liberates itself from the shriveled remnant of its hatching skin, and becomes a free new creature in the world. Being a grasshopper, it proceeds to jump, and with its first efforts clears a distance of four or five inches, something like fifteen or twenty times the length of its own body.
When the young locusts hatch under normal undisturbed conditions, however, we must picture them as coming out of the eggs into the cavernous spaces of the egg pod, and all buried in the earth. They are by no means yet free creatures, and they can gain their liberty only by burrowing upward until they come out at the surface of the ground. Of course, they are not very far beneath the surface, and most of the way will be through the easily penetrated walls of the cells of the egg covering. But above the latter is a thin layer of soil which may be hard-packed after the winter's rains, and breaking through this layer can not ordinarily be an easy task. Not many entomologists have closely watched the newly-hatched grasshopper emerge from the earth, but Fabre has studied them under artificial conditions, covered with soil in a glass tube. He tells of the arduous efforts the tiny creatures make, pressing their delicate bodies upward through the earth by means of their straightened hind legs, while the vesicles on the back of the neck alternately contract and expand to widen the passage above. All this, Fabre says, is done before the hatching, skin is shed, and it is only after the surface is reached and the insect has attained the freedom of the upper world that the inclosing membrane is cast off and the limbs are unencumbered.
The things that insects do and the ways in which they do them are always interesting as mere facts, but how much wiser might we be if we could discover why they do them! Consider the young locust buried in the earth, for example, scarcely yet more than an embryo. How does it know that it is not destined to live here in this dark cavity in which it first finds itself? What force activates the mechanism that propels it through the earth? And finally, what tells the creature that liberty is to be found above, and not horizontally or downward? Many people believe that these questions are not to be answered by human knowledge, but the scientist has faith in the ultimate solution of all problems, at least in terms of the elemental forces that control the activities of the universe.
We know that all the activities of animals depend upon the nervous system, within which a form of energy resides that is delicately responsive to external influences. Any kind of energy harnessed to a physical mechanism will produce results depending on the construction of the mechanism. So the effects of the nerve force within a living animal are determined by the physical structure of the animal. An instinctive action, then, is the expression of nerve energy working in a particular kind of machine. It would involve a digression too long to explain here the modern conception of the nature of instinct; it is sufficient to say that something in the surroundings encountered by the newly-hatched grasshopper, or some substance generated within it, sets its nerve energy into action, that the nerve energy working on a definite mechanism produces the motions of the insect, and that the mechanism is of such a nature that it works against the pull of gravity. Hence the creature, if normal and healthy in all respects, and if the obstacles are not too great, arrives at the surface of the ground as inevitably as a submerged cork comes to the surface of the water. Some readers will object that an idea like this destroys the romance of life, but whoever wants romance must go to the fiction writers; and even romance is not good fiction unless it represents an effort to portray some truth.
Insects hatched from eggs laid in the open may begin life under conditions a little easier than those imposed upon the young grasshopper. Here, for example (Fig. 7), are some eggs of insects belonging to the katydid family. They look like flat oval seeds stuck in overlapping rows, some on a twig, others along the edge of a leaf. When about to hatch, each egg splits halfway down one edge and crosswise on the exposed flat surface, allowing a flap to open on this side, which gives an easy exit to the young insect about to emerge. The latter is inclosed in a delicate transparent sheath, within which its long legs and antennae are closely doubled up beneath the body; but when the egg breaks open, the sheath splits also, and as the young insect emerges it sheds the skin and leaves it within the shell. The new creature has nothing to do now but to stretch its long legs, upon which it walks away, and, if given suitable food, it will soon be contentedly feeding.
(Continues...)
Excerpted from Insects by Robert Evans Snodgrass. Copyright © 2015 Robert Evans Snodgrass. Excerpted by permission of Dover Publications, Inc..
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Table of Contents
Contents
Preface, i,I. The Grasshopper, 1,
II. The Grasshopper's Cousins, 26,
III. Roaches and Other Ancient Insects, 77,
IV. Ways and Means of Living, 99,
V. Termites, 125,
VI. Plant Lice, 152,
VII. The Periodical Cicada, 182,
VIII. Insect Metamorphosis, 226,
IX. The Caterpillar and the Moth, 262,
X. Mosquitoes and Flies, 314,
Index, 355,