Elementary Study of Insects

<h2><SPAN name="Chapter_I" id="Chapter_I"></SPAN><span class="smcap">Chapter I</span><br/><br/> INSECTS</h2> <div class="blockquot"><p>"<i>There is a difference between a grub and a butterfly; yet your butterfly was a grub.</i>"</p> <p class="bauthor">&mdash;<span class="smcap">Shakespeare.</span></p> </div> <p class="cap"><span class="dcap">In</span> undertaking a study of insects it is well first of all to know something about what they are, their general nature, appearance, habits and development. The insects comprise the largest group of animals on the globe. There are about four times as many different kinds of insects as all other kinds of animals combined. Insects vary greatly in size. Some are as large as small birds, while others are so small that a thousand placed in one pile would not equal the size of a pea.</p> <p>Insects are commonly spoken of as "bugs." This term, however, is properly used only when referring to the<span class="pagenum"><SPAN name="Page_2" id="Page_2">[2]</SPAN></span> one order of insects which includes the sap and blood-sucking insects such as the chinch bug, bed-bug, squash bug, and the like. Then too, there are many so-called "bugs" which are not insects at all. Spiders, thousand-legs, crawfishes and even earth-worms are often spoken of as bugs.</p> <h3><i><SPAN name="What_They_Are" id="What_They_Are"></SPAN>What They Are</i></h3> <div class="figcenter"> <ANTIMG src="images/003.png" width-obs="700" height-obs="274" alt="" title="" /> Side view of grasshopper with wings and legs partly removed. Note the division of the body into head, thorax, composed of prothorax, mesothorax and metathorax, and abdomen consisting of ring-like segments.</div> <p>Insects are variously formed, but as a rule the mature ones have three and only three pairs of legs, one pair of feelers, one pair of large eyes, and one or two pairs of wings. The body is divided into a head, thorax and abdomen.<span class="pagenum"><SPAN name="Page_3" id="Page_3">[3]</SPAN></span> The head bears the eyes, feelers and mouth, the thorax bears the legs and wings, and the abdomen is made up of a number of segments. The presence of wings at once decides whether or not it is an insect, for, aside from bats and birds, insects alone have true wings. These are the distinguishing characters of the full grown insect, but, like birds, they hatch from eggs and while young do not always look like their parents. When young they may take on various shapes as caterpillars, borers, maggots, grubs, hoppers, and the like. Young insects are often difficult to distinguish from true worms, centipedes, snails, and such forms, but after one has collected and reared some of the young and watched them pass through the different stages and emerge with wings they are much more easily recognized.</p> <h3><i><SPAN name="Their_Principal_Characteristics" id="Their_Principal_Characteristics"></SPAN>Their Principal Characteristics</i></h3> <div class="figcenter"> <ANTIMG src="images/004.png" width-obs="311" height-obs="250" alt="" title="" /> Face of grasshopper enlarged showing parts; ant., antenna; eye, compound eye; oc., ocellus or simple eye; cl., clypeus; lbr., labrum or upper lip; mx. p., maxillary palpus; lb. p., labial palpus; lab., labium or lower lip.</div> <div class="figright"> <ANTIMG src="images/005.png" width-obs="250" height-obs="296" alt="" title="" /> Mouth parts of grasshopper shown in relative position; lbr., labrum; md., mandibles; hyp., hypopharynx; max., maxillae; lab., labium.</div> <p>Young insects as a rule are soft like caterpillars and maggots, while the old<span class="pagenum"><SPAN name="Page_4" id="Page_4">[4]</SPAN></span> ones usually have a hard body wall, similar to the beetles and wasps. The wings are usually thin and transparent though in some cases they are leathery or hard as in case of beetles or covered with scales as in the butterflies. The three pairs of legs are jointed and used for running, climbing, jumping, swimming, digging or grasping. The feelers or antennae are usually threadlike, clubbed, or resemble a feather<span class="pagenum"><SPAN name="Page_5" id="Page_5">[5]</SPAN></span> and extend forward or sidewise from the head. The large eyes are compound, being made up of many great small units which, when magnified, resemble honey-comb. In some cases two or three small bead-like eyes may be present besides the two large eyes. The mouth parts of insects may be formed for chewing, as in the grasshopper, or for sucking up liquids, as in the mosquito. The mouth of an<span class="pagenum"><SPAN name="Page_6" id="Page_6">[6]</SPAN></span> insect is built on an entirely different plan from our own. Chewing insects have an upper and lower lip and between these there are two pairs of grinding jaws. These jaws are hinged at the side of the face and when chewing they come together from either side so as to meet in the middle of the mouth. They therefore work sidewise rather than up and down. The mouth parts of the sucking insects are drawn out to form a sucking tube or proboscis as in case of the butterfly or mosquito.</p> <div class="figleft"> <ANTIMG src="images/006.png" width-obs="250" height-obs="170" alt="" title="" /> Leg of grasshopper showing segmentation. The basal segment c, is the coxa, the next t, the trochanter, the large segment f, the femur, the long slender one ti, the tibia, and the three jointed tarsus ta, with claws at the tip.</div> <p style="clear: right;">The internal organs of insects are similar to those of other animals. The digestive tube consists of oesophagus, gizzard, or stomach, and intestines. The nervous system is well developed as shown by the extreme sensitiveness of insects to touch. The brain is comparatively small except in the bees and ants. The circulatory system consists simply of a long tube heart, the blood vessels being absent. In this way the internal organs of the insect are simply<span class="pagenum"><SPAN name="Page_8" id="Page_8">[8]</SPAN></span> bathed in the blood. The system of respiration is most complicated. The air is taken in through pores usually along the side of the body and is then carried through fine tracheal tubes to all parts of the body. You cannot drown an insect by putting its head under water, since it does not breathe through its mouth. The muscular system is similar to that of other animals which have the skeleton on the outside.</p> <div class="figcenter"><SPAN name="Page_7" id="Page_7"></SPAN> <ANTIMG src="images/007.png" width-obs="456" height-obs="550" alt="" title="" /> The internal organs of the honey bee. Note the strong wing muscles in the thorax. The tube-like heart begins in the head and extends back through the thorax and follows the curve of the abdomen. Below the heart is the digestive tube consisting of the slender oesophagus which extends back to the expanded honey stomach, in which the bee carries the nectar it collects from flowers, then the curled true stomach, the small intestine and expanded large intestine. Below this is the nervous system consisting of the brain and a chain of connected enlargements or ganglia extending back into the abdomen in the lower part of the body. The respiratory system in part appears just above the honey stomach, and the black circular or oval spots are cross sections of connecting air tubes, which run all through the body. Also note the sting with the poison gland and sack which are pulled out with the sting; also the sucking tube for getting honey from flowers, and the structures on the legs for gathering and carrying pollen; the pollen basket is on the back side of the hind leg.</div> <h3><i><SPAN name="Their_Methods_of_Developing" id="Their_Methods_of_Developing"></SPAN>Their Methods of Developing</i></h3> <p>In most cases the parent insect deposits small eggs which hatch later into the young insects. In some cases, as with the blow-flies, the maggot may hatch from the egg while yet in the parent's body, when the active larva is born alive. Whether the egg hatches before or after it is deposited, the young insect continues to develop in one of three ways. It may resemble the parent and simply grow as does a kitten, or it may look somewhat like its parent though smaller and without<span class="pagenum"><SPAN name="Page_9" id="Page_9">[9]</SPAN></span> wings, as the young grasshopper, or it may bear no resemblance whatever to the parent, as the caterpillar which feeds and grows and finally spins a cocoon<span class="pagenum"><SPAN name="Page_10" id="Page_10">[10]</SPAN></span> in which it passes to the resting chrysalis stage and later emerges with wings. The development of insects is therefore extremely complicated.</p> <div class="figcenter"> <ANTIMG src="images/008.png" width-obs="335" height-obs="400" alt="" title="" /> The chinch bug showing development with incomplete metamorphosis; a, egg; b, first nymph; c, second nymph; d, third nymph; e, fourth nymph; f, adult winged bug; g, chinch bugs extracting sap from corn plant. To control this pest burn over all winter harboring places and use chemical or dust barriers following wheat harvest.</div> <h3><i><SPAN name="The_Principal_Orders" id="The_Principal_Orders"></SPAN>The Principal Orders</i></h3> <p>In order to study a group of animals which includes so many thousand different kinds it is necessary to divide them into a number of sharply defined divisions or orders. All animal life is naturally grouped into such divisions and subdivisions. Among the insects we at once detect seven large, sharply defined divisions or orders, and ten or more smaller ones. Of these we have first, the two-winged true flies; second, the four-winged butterflies and moths; third, the hard-backed beetles; fourth, the stinging four-winged wasps and bees; fifth, the variously formed sucking insects or true bugs, as chinch bugs and bed-bugs; sixth, the rapid-flying four-winged snake doctors or dragon-flies and, seventh, the hopping forms, the grasshoppers. Besides these<span class="pagenum"><SPAN name="Page_11" id="Page_11">[11]</SPAN></span> we have the various smaller orders of water-loving insects, fleas, etc. The<span class="pagenum"><SPAN name="Page_12" id="Page_12">[12]</SPAN></span> seven groups mentioned above include the majority of our common forms and in the studies to follow we will include only representatives from these orders.</p> <div class="figcenter"> <ANTIMG src="images/009.png" width-obs="324" height-obs="400" alt="" title="" /> The Hessian fly showing development with complete metamorphosis; a, egg; b, larva or maggot; c, flax-seed stage; d, pupa; e, adult winged fly; f, wheat stubble with flax-seed stages near base taken after harvest. To control this pest, plow under stubble after harvest; keep down all volunteer wheat and sow wheat after fly-free date in the fall.</div> <h3><i><SPAN name="Their_Habits" id="Their_Habits"></SPAN>Their Habits</i></h3> <p>The habits of insects are as varied as their forms and adaptations. Some live in the water all their life, others spend a part of their life under water, others live the care-free life of the open air, others enjoy feeding upon and living in the foulest of filth, others associate themselves with certain definite crops or animals thereby doing untold injury, while others produce food and other materials which are to be used by man for his comfort. Every imaginable nook and crook, from the depths of lakes to the tops of mountains, from the warm, sunny south to the cold frigid north, from the foul damp swamps to the heart of our desert lands, offers a home for some small insect.<span class="pagenum"><SPAN name="Page_13" id="Page_13">[13]</SPAN></span></p> <p>The most striking habits and developments among insects is found in the more highly advanced families of bees and ants where definite insect societies are formed, resembling in many respects human societies and human activities. Among these villages are established, homes built, battles fought, slaves made, herds kept by shepherds, and even fields cultivated. In these groups we have the nearest approach to human intelligence.</p> <h3><i><SPAN name="Their_Role_in_Agriculture" id="Their_Role_in_Agriculture"></SPAN>Their Role in Agriculture</i></h3> <p>Some insects may be very destructive to crops, others are beneficial, while the majority of insects are of no importance to man or agriculture. The various forms of pests such as the chinch bug, potato beetles, and others do an enormous amount of damage each year. They destroy hundreds of millions of dollars worth of crops annually in the United States alone. They devour enough to pay for the entire cost of running the school system<span class="pagenum"><SPAN name="Page_14" id="Page_14">[14]</SPAN></span> of our country and nearly enough to meet all the expenses of our government. In view of these facts it is the duty of each and every farmer, young or old, to acquaint himself with these destructive pests and prepare himself for combating them. With a knowledge of the methods of controlling these pests much of this enormous loss can be prevented.</p> <p>While some insects are extremely injurious, others are very helpful. The products of the honey bee in the United States alone amount to several million dollars a year, to say nothing of its value to the farmer in pollinating fruits. The annual output of silk, all of which is spun by the silkworm, is worth millions of dollars. Many other forms are of value to man by producing material of commercial value such as lac, shellack, dyes, medicines, etc. Of all the beneficial insects those which are of greatest value to man are the parasites and similar forms which help to keep in check many of<span class="pagenum"><SPAN name="Page_15" id="Page_15">[15]</SPAN></span> the severest pests of the farm. Insects are not all bad fellows by any means. One must acquaint himself with those which are good and those which are bad before he can hope to deal with them intelligently.</p> <hr style='width: 45%;' /> <div class="cpoem" style="width: 20em;"><div class="poem"><div class="stanza"> <span class="i0">"<i>And with childlike credulous affection</i><br/></span> <span class="i2"><i>We behold those tender wings expand,</i><br/></span> <span class="i0"><i>Emblems of our own great resurrection,</i><br/></span> <span class="i2"><i>Emblems of the bright and better land.</i>"<br/></span></div> </div></div> <p class="author"><span class="smcap">&mdash;Longfellow.</span></p> <hr style="width: 65%;" /><p><span class="pagenum"><SPAN name="Page_16" id="Page_16">[16]</SPAN></span></p> <div style="break-after:column;"></div><br />