Entomology (Gr. insect, from cut in, and discourse), the branch of natural history which treats of insects, one of the classes of articulated animals. That part of the science which refers to the anatomy and physiology of the class will be treated under the head of Insects ; and the particular descriptions of orders, families, genera, and species will be found under their various scientific and popular titles. This article will be devoted to the history of entomology, and to brief sketches of the principal systems of classification. - In entomology, more perhaps than in any other department of natural history, does the student feel the want of a natural classification; but, as the best authors have devoted very unequal study to different groups, from the impossibility of fully cultivating every portion of the immense field, no classification complete and natural in all its parts can be found. The nearly 100,000 species now described probably do not form one half of the total number in existence.
If we take for a basis the comparative ratio which has been found to exist in Germany between insects and plants, that of 2 to 1, and extend this to the whole world, we shall have in round numbers at least 400,000 species of insects inhabiting the earth. - It appears that Aristotle, the father of natural history, separated insects from Crustacea, and divided them into winged and wingless, subdividing these last into several natural minor groups so successfully as to excite the surprise and admiration of modern observers. From Aristotle we may pass over a period of 1,800 years, a blank as far as the progress of natural history is concerned, to the middle of the 16th century, when Gesner, a Swiss, revived the study of animals, leaving valuable papers on insects from personal observation, which were published after his death by Mouffet, in 1634. During the next 100 years Aldrovandus divided insects into two chief groups, land and water insects, subdividing them according to the structure of their wings and legs; Hoefnaegel made beautiful figures of them; Redi studied their origin and mode of propagation; Malpighi made a careful dissection of the silkworm; Goedart and Vallis-nieri described the metamorphoses of insects; Leeuwenhoeck examined them microscopically ; and Mme. Merian studied the development of the lepidoptera, going to Surinam in her scientific zeal to continue her observations among the most gorgeous species.
The writings of Swammerdam, a Dutch naturalist in the middle of the 17th century, created a new epoch in the annals of entomology. He studied the metamorphoses of insects, and from these introduced the first attempts toward a natural classification. His system was as follows: I. Insects without a metamorphosis, changing their skin but not their form, as spiders, lice, wood lice, and myriapods. II. Insects with a metamorphosis : a, those moving in all stages of existence, at first wingless, then with rudimentary and finally with entire wings, including what are now called neuroptera, orthoptera, and hemiptera; b, motionless in the pupa state, but having limbs, including the hymenoptera, coleoptera, and lepidoptera; c, ovate pupae, wingless and motionless, as the diptera. - John Ray, an English clergyman living in the latter part of the 17th century, was the first true systematise and doubtless furnished Linnaeus with many of the ideas afterward successfully worked out by him. In a " History of Insects," published after his death in 1705, is the following arrangement : I. Insects without metamorphosis, including - 1, apoda (annulate worms) terrestrial and aquatic; 2, pedata, including the terrestrial (lice) and aquatic hexapods, the octo-pods (spiders), lobsters and crabs, the terrestrial polypods (centipedes and wood lice), and the aquatic polypods (amphipoda and isopoda of Latreille). II. Insects with metamorphosis, including - 1, those with moving larvae and pupae (orthoptera and hemiptera); and 2, those with motionless pupae, as coleoptera, lepidoptera, diptera, and hymenoptera.
III. Insects with simple metamorphosis, moving through most of the stages, like the dragon flies. - Reaumur, in the early part of the 18th century, published his Memoires pour servir a l'histoire des insectes, affording valuable information on the habits of insects, but wanting in systematic arrangement. About the same time, in 1735, appeared the Systema Naturoe of Linnaeus, who displayed in the classification of insects the same intuitive perception of the characters of groups that is observable in his other branches of the animal kingdom. His system is based on the characters of the wings and the presence or absence of a sting, as follows: I. Insects with four wings, including the following orders: 1, coleoptera, with the anterior wings crustaceous, with a straight suture; 2, hemiptera, with semicrustaceous incumbent anterior wings; 3, lepidoptera, with all the wings covered with scales; 4, neuroptera, with all the wings membranous, and with no sting in the tail; 5, hymenoptera, with membranous wings and tail armed with a sting. II. Insects with two wings, comprising, 6, diptera, with poisers in place of the posterior pair. III. Insects with neither wings nor elytra, including, 7, aptera, in which were placed by Linnaeus the hexapod lice, fleas, etc, spiders, crabs, and centipedes.
The fault of this system is its exclusive principle of division drawn from the wings, which placed among the aptera animals far removed from insects proper. - De Geer, a Swede, published a work on insects between 1752 and 1778, having the same title as that of Reaumur, of which it may in some respects be considered the sequel; his system is intermediate between that of Linnaeus and that of Fabricius, who came after him, being based both upon the organs of flight and those of manducation, and according to Mr. Kirby is more natural than that of either of the above named naturalists. It is as follows : I. Insects with wings, alata, including - A. Gymnoptera, or those with four wings without cases, with the subdivisions : 1, lepidoptera, with scaly wings and spiral tongue;
2, elingula, with naked membranous wings, no teeth nor tongue (trichoptera, ephemerina);
3, neuroptera, with membranous, equal, reticulated wings, and teeth in the mouth (as libel-lula and other Linnaean neuroptera); 4, hymenoptera, with membranous unequal wings, teeth in the mouth, and a sting or borer in the females; 5, siphonata, with membranous wings and tongue bent beneath the breast (homoptera of Leach), including the aphides and cicada. B. Vaginata, or those with two wings covered by elytra, with the subdivisions : 6, dermaptera, with elytra half coriaceous and half membranous, crossed, a pair of membranous wings, and tongue bent beneath the breast (hemiptera of Leach), as the bugs and water bugs; 7, orthoptera, cockroaches and grasshoppers; 8, with teeth in the mouth, and the wings of beetles (coleoptera). C. Diptera, with two uncovered wings, including - 9, halterata (the diptera of Linnaeus), having a pair of poisers, mouth with a tongue without teeth; 10, pro-boscidea (like the genus coccus), with no poisers, tongue, or teeth in the male, and no wings, but a tongue in the breast of the female.
II. Insects without wings, aptera, including - D. Saltatoria, with the subdivision : 11, suctoria (culex), undergoing metamorphosis, with six legs, and mouth with tongue, the aphaniptera of Kirby. E. Gressoria, with the subdivisions: 12, aucenata, undergoing no metamorphosis, with six legs, and head and trunk distinct, as termes, pediculus, psocus; 13, atrachelia, spiders and crabs; 14, Crustacea, as isopods, am-phipods,' and myriapods. This system, though not purely artificial, and founded on several correct principles, is yet far from natural, and includes among insects animals which do not belong with them; his 14 orders comprised only about 1,500 species, referable to 100 genera. - Geoffroy, in France, in 1762, published a system which is important from the introduction of the joints of the tarsi as a means of classification; he makes only six groups, coleoptera, hemiptera, lepidoptera, te-traptera, diptera, and aptera, the third, fifth, and sixth being the same as the Linnaean; it is an exceedingly unnatural system. - Fabricius, a German, a pupil of Linnaeus, introduced important improvements into the science during the last quarter of the 18th and the beginning of the 19th century; his system is based upon the number, proportions, form, and situation of the parts which constitute the mouth, without regard to other parts of the insect; by building upon this narrow foundation he departed widely from nature, though by drawing attention to the maxillary system he has enabled his successors to define certain groups with considerable accuracy.
His first classification of 1775 was greatly modified in the course of his life, and the following was proposed by him in his Entomologia in 1798:
I. INSECTS WITH BITING MOUTHS.
Two pairs of mandibles.
a. The lower ones having palpi.
1. Free without covering....
Class eleutherata (beetles).
" ulonata (orthoptera).
3. Connate with the labium...
" synistata (neuroptera).
4. Distended, thin, coriaceous...
" piezata (hymenoptera).
5. Horny, strongly toothed, labium without palpi...
" odonata (libelluloe).
b. All without palpi...........
" mitosata (scolopendra).
A pair of scissor-like maxillae....
" unogata (scorpions and spiders).
More than two pairs of maxillae.
1. Within the labium...
" polygonata (isopoda).
2. Outside the lip, closing the mouth...
" pleistagnatha (short-tailed crabs).
3. Outside the lip, but covered by the palpi...
" exochnata (long-tailed crabs).
II. INSECTS WITH SUCTORIAL MOUTHS.
1. In the mouth a spiral tongue...
Class glossata (lepidoptera).
2. A horny probosels, with jointed sheaths...
" rhyngota (hemiptera).
3. A soft, unjointed probosels...
" antliata (diptera).
The facility with which genera were determined by this system secured for it many followers, in spite of its unnaturalness; and Illiger, by uniting it with that of Linnaeus, considerably improved it. He made order of Linnaeus correspond with class 1 of Fabri-cius; 2 L. with 2 and 12 F.; 3 L. with 11 F.; 4 L. (to which were added termes, lepisma, and podura) with 3 and 5 F.; 5 L. with 4 F.; 6 L. (with pediculus and acarus) with 13 F.; and 7 L. (without the above named apterous genera) with 6, 7, 8, 9, and 10 F. - Olivier, in the article Insectes in the Encyclopedic methodique, follows chiefly the Linnaean classification, modified by Geoffroy and De Geer, making use of the wings and elytra, the parts of the mouth, and the joints of the tarsi in his divisions; he substituted the term orthoptera for the der-maptera of De Geer; in his order aptera are still included spiders, crabs, and myriapods. In Olivier's great work on coleoptera, in six large quarto volumes with nearly 400 plates, published between 1789 and 1808, may be found the largest collection of representations of this order yet known. - Latreille's first work, published in 1796, presents the insects of Linnaeus in 14 classes, adding orthoptera to the Linnaean system, and separating the aptera in to suctoria, thysanoura, parasita, acephala, ento-mostraca, Crustacea, and myriapoda; this system, though in many respects unnatural, claims the positive merit of introducing some natural families.
In 1810 he adopted a new classification, following Cuvier and Lamarck in separating Crustacea and arachnids from insects proper, and dividing the latter into the 7 orders of his first classification, adding the order suctoria (formed entirely by the genus pulex). In 1817 he added myriapoda, thysanoura, and parasita to his 8 orders, and also strepsiptera of Kirby; in 1825 he raised the myriapoda, after Leach, to a distinct class, and divided the insecta into 11 orders; in 1829 he reduced the myriapoda to an order among insects, raising the number again to 12 orders, and in 1832 raised them again to a class intermediate between arachnids and insects. One great merit of Latreille is that he gave family names to the groups of genera, which Macleay has reduced to system by giving to them the termination idoe, which, if not always classically correct, is of advantage for uniformity and euphony. - Lamarck divides insects into 8 orders: 1. Insects with suctorial mouths: 1, aptera (suctoria, Latr.); 2, diptera; 3, hemip-tera; 4, lepidoptera. II. Insects with man-dibulate mouths: 5, hymenoptera; 6, neuroptera; 7, orthoptera; and 8, coleoptera.
Other aptera he placed among arachnids and Crustacea, and ranked thysanoura, myriapoda, and parasita among arachnids. - Dumeril places insects above mollusca in the animal series, and comprises among them arachnids and myriapods; his arrangement differs but little from the Linnaean; he endeavored to reunite the greatly divided families, and to reduce the number of genera. - The philosophical systems of the modern German school proceed on the view that organic nature is one great whole, exhibiting progressive grades of development, which are characterized as classes. Oken has made 13 classes of animals, each represented by a successively added organ. Insects form the 9th class, and are called lung animals; they are divided as follows: I. Germ flies, with perfect metamorphosis, with tribes: 1, hemiptera; 2, orthoptera and dermaptera; 3, neuroptera. II. Sexual flies, with perfect metamorphosis and equal wings, with tribes: 4, diptera and suctoria; 5 hymenoptera; 6, lepidoptera. III. Lung flies, beetles, with perfect metamorphosis, elytra, and wings, with tribes: 7, G. tetrame-ra; 8, C. heteromera; and 9, C. pentamera. - Among the English writers who have contributed to the advance of entomological classification may be mentioned Leach, Kirby, and Macleay. Dr. W. E. Leach published several elaborate treatises on insects in the "Linnaean Transactions," and in the British and foreign encyclopaedias; his system is sketched in vol. iii. of the "Zoological Miscellany." He divides insects into ametabola and metabola, according to the absence or occurrence of metamorphosis, the former including 2 and the latter 14 orders; he subdivides orthoptera into 3 orders, adding dermaptera (forficula) and dictyoptera, and introduces also omoptera and omaloptera.
The classification of Kirby and Spence, as given in vol. iv. of the " Introduction to Entomology " (1815-'26), is as follows: I. Mandibulata, or insects with mandibles, containing the orders: 1, coleoptera; 2, strepsiptera; 3, dermaptera; 4, orthoptera; 5, neuroptera; and 6, hyme-noptera. II. Haustellata, or insects with suctorial mouths, containing the orders: 7, hemip-tera; 8, trichoptera; 9, lepidoptera; 10, dip-tera; 11, aphaniptera; and 12, aptera (all wingless insects breathing through tracheae). It has been objected to this system that the 3d order is improperly separated from the 4th, and that the 8th forms naturally a part of the 5th. The system of Macleay is founded on the following principles: 1, all natural groups return within themselves, and consequently present themselves in the form of circles; 2, each of these circles contains five others, connected in the same way; 3, where the circles join, there are intermediate groups connecting them more closely; 4, the members of each, at the points where the circles meet, exhibit analogies.
The animal kingdom consists of five circles, one of which, the annulosa (crustacea and insects), consists of five principal groups, which may be represented as follows:
The three orders of ametabola, mandibulata, and haustellata only concern us here. Of the first, the myriapods join the crustacea, and the thysanoura and anoplura (parasita) join the mandibulata. The haustellata and mandibulata he calls insecta ptilota; the former include lepidoptera, diptera, aptera (suctoria, Latr.), hemiptera, and homoptera; the latter include trichoptera, hymenoptera, coleoptera, orthoptera, and neuroptera. These two circles are contiguous in the trichoptera and lepidoptera, the genus mystacides (Latr.) of the former making the transition to aglossa (Latr.) of the latter. Space will not permit the introduction of the families which he considers the connecting links between the orders of the two great divisions. This system, while it has many forced and unnatural affinities, presents much that is valuable in determining the groups of transition, which are found among insects as among other branches of the animal kingdom. His principal work, Horoe Entomologicoe, was published in 1819-21. - Burmeister divides insects, according to the completeness of their metamorphosis, into ametabola and metabola, each group presenting both haustellata and mandibulata, and subdivided according to the form of the larva, the structure of the wings, and the internal organization.
His system is as follows: I. Insecta ametabola, with imperfect metamorphosis; the larva, pupa, and perfect insect resembling each other, the pupa eating and moving about: A. Having a suctorial mouth, with four fine setae enclosed in a sheath, and the palpi wanting, with order 1, hemiptera (bugs). B. With a masticating mouth : a, with four unequal wings, anterior ones leathery, the posterior membranous and folded longitudinally and once transversely; protho-rax free, and many biliary vessels; with order 2, orthoptera (locusts); b, with four generally equal wings, never folded, with order 3, dicty-otoptera (cockroaches). II. Insecta metabola, with perfect metamorphosis; the larva a worm, of 13 segments, with or without legs; the pupa motionless, or, if it moves, not eating. A. With suctorial mouth: a, with two naked transparent wings, the posterior replaced by pedicu-lated knobs; four biliary vessels; larvae without feet; soft proboscis, with several setae and a pair of palpi; prothorax not free; with order 4, diptera (flies); b, with four wings, generally covered with scales, six biliary vessels; larvae with feet and a distinct head; the maxillae forming a spiral tongue; prothorax not free, but closely connected with the mesotho-rax; with order 5, lepidoptera (butterflies and moths). B. With masticating mouth, or at least visible mandibles and palpi: a, with four equally large or long wings, with reticulated ner-vures; rarely more than eight biliary vessels; prothorax always free; with order 6, neuroptera (dragon flies); b, with four unequal wings, with variously branching nervures; larvae generally without head or feet, yet sometimes with both; many biliary vessels; prothorax not free; with order 7, hymenoptera (bees, wasps); c, with four unequal wings, the anterior ones corneous; larvae with head, with or without feet; four or six biliary vessels; prothorax always free; with order 8, coleoptera (beetles). In almost all these orders there are apterous families, genera, and species, whose place may be determined by their metamorphosis and the structure of the mouth; but they never form a distinct order like the aptera of Latreille. Burmeister maintains that all true insects undergo some metamorphosis, though in the apterous forms it may be difficult to detect it from the absence of the wings; as his idea of an insect necessitates metamorphosis, however imperfect, he gives the name ametabola (applied by Leach to apterous insects) to all those with an imperfect metamorphosis, as there is no real deference in the process of development in each. - Westvvood, in his "Introduction to the Modern Classification of Insects," in 1839, gives the following:
Osculant order, strepsiptera. " coleoptera.
Osc. ord. euplexoptera. " orthoptera. " neuroptera. " trichoptera.
Osc. ord. homaloptera. " aphaniptera.
heteroptera (includ-ing the water bugs).
" homoptera. " lepidoptera.
- Stephens, in the article "Insecta," in vol. ii. of the "Cyclopaedia of Anatomy and Physiology" (1839), divides insects into: I. Mandibulata, containing coleoptera, dermap-tera (earwigs), orthoptera, neuroptera, tri-choptera, (caddis flies), hymenoptera, and strepsiptera; and II. Haustellata, containing lepidoptera, diptera, homaloptera, aphaniptera, aptera, hemiptera, and homoptera. - Siebold (Burnett's translation), in 1848, gives the following classification : A. Insects without metamorphosis, ametabola, containing - 1, aptera (pediculidoe, &c). B. With incomplete metamorphosis, hemimetabola, containing - a, with suctorial mouth: 2, hemiptera; b, with mandibulate mouth : 3, orthoptera. C. With complete metamorphosis, holometabola, containing - a, with suctorial mouth: 4, diptera; 5, lepidoptera; 6, hymenoptera; b, with mandibulate mouth: 7, strepsiptera; 8, neuroptera; and 9, coleoptera. This is the same as the classification of Vogt, founded upon em-bryological principles; and the orders are the same as those of Owen, as given in the second edition of his " Lectures on the Comparative Anatomy and Physiology of the Invertebrate Animals " (1855), except that homoptera is substituted by him for hemiptera.
The orders of Milne-Edwards, in his Cours elementaire d'his-toire naturelle (1855), are nearly the same as Siebold's, except that aptera is omitted, rhipip-tera substituted for strepsiptera, and anoplu-ra and thysanoura are added. The embryo-logical system of Van Beneden (1855) is the same as the last, the term strepsiptera being reintroduced, and parasita substituted for ano-plura. - Prof. Agassiz, in the "Smithsonian Contributions to Knowledge" (vol. ii., 1851), gives the following classification of insects from embryological data:
I. Chewing Insects (man-dibulata). Neuroptera. Coleoptera. Orthoptera. Hymenoptera.
II. Sucking Insects (haus-tellata). Hemiptera. Diptera. Lepidoptera.
In this the subdivisions are made according to their transformations. From the fact that those undergoing complete metamorphosis have a chewing apparatus in the early stages of their growth, which is gradually transformed into various kinds of suckers, he expresses the belief that the mandibulata are lower than the haustellata; and he also ranks lepidoptera highest among insects, and not coleoptera, as generally maintained. Mr. A. S. Packard, in his "Synthetic Types of Insects" (1872), makes seven sub-orders, viz. : hymenoptera, lepidoptera, diptera, coleoptera, hemiptera, orthoptera, and neuroptera. - Mr. Wilson in the article "Entomology " in the "Encyclopaedia Britannica," Dr. Burnett in his translation of Siebold, and Mr. Westwood, give valuable lists of the authors on this science, arranged in chronological order; from them we select the following as among the most important writers since La-treille: in England, Donovan, Curtis, Wood, Rennie, Haliday, A. White, Doubleday, Shuck-ard, Hope, Newman, and Newport; in France, Jurine, Dufour, Godart, Guerin - Meneville, Boisduval, Dejean, Lacordaire, and Blanchard; in Germany, Meigen, Ochsenheimer, Klug, Fischer von Waldheim, and Germar; in Sweden, Fallen; in America, Thomas Say, Dr. T. W. Harris, J. L. Leconte, S. II. Scudder, A. S. Packard, and Dr. Hagen. The most useful work on entomology ever published in this country is the " Treatise on some of the Insects of New England which are Injurious to Vegetation," by Dr. T. W. Harris, issued by order of the legislature of Massachusetts; the second edition was published in 1852, and the third, edited by Charles L. Flint, in 1862, with illustrations, at the expense of the state.
In this work are adopted the seven following orders, as generally received by naturalists: I. Coleoptera (or beetles), with jaws, two thick wing covers meeting in a straight line on the top of the back, and two filmy, transversely folded wings; metamorphosis complete; larvae generally with six true legs and sometimes with a terminal prop leg, rarely without legs; pupa with wings and legs distinct and unconfined. II. Orthoptera (cockroaches, crickets, &c), with jaws, two opaque upper wings overlapping a little on the back, and two larger thin wings folded in fan-like plaits; transformation partial; larvae and pupae active, but without wings. III. Hemiptera (bugs and plant lice), with a horny beak for suction; four wings, of which the upper lie flat, cross each other on the back, and slope at the sides like a roof; transformation partial; larvae and pupae like the adults, but wingless. IV. Neuroptera (dragon flies, May flies, white ants, &c), with jaws, four netted wings, the hinder the largest; with no sting nor piercer; transformation complete or partial; larva and pupa various.
V. Lepidoptera (butterflies and moths), with a sucking tube; four scaly wings; transformation complete; larvae with six true legs, and from four to ten prop legs; pupa with the cases of the wings and legs indistinct, and soldered to the breast. VI. Hymenoptera (bees, wasps, ants), with jaws; four veined wings, the hinder pair generally the smallest; a sting at the end of the abdomen; transformation complete; larvae like maggots, or slugs, or caterpillars; pupae with the legs and wings unconfined. VII. Diptera (flies, mosquitoes, &c), with a horny or fleshy proboscis, two wings and two balancers or poisers behind them; transformation complete; larvae footless maggots, with the breathing holes generally in the hinder part of the body; pupae usually incased in the dried skin of the larvae, but sometimes naked, in which case the wings and legs are visible, and more or less free. - Among the smaller groups, the order strepsiptera (Kirby), or rhipiptera(Latr.), contains minute insects which undergo their transformations within the bodies of bees and wasps; the maggot-like larvae live between the rings; the females are wingless, and never leave the body of their host; the adult males have two very short members instead of fore wings, and two very large hind wings; the sharp-pointed jaws are adapted for piercing rather than biting.
Their systematic position is not precisely determined; Latreille places them between lepidoptera and diptera, though he thinks them most nearly allied to some of the hymenoplera. The order aptera (Leach), suctoria (De Geer), siphonaptera (Latr.), or aphaniptera (Kirby), is constituted by the flea tribe, which seem to be intermediate between hemiptera and diptera. The earwigs, included by most entomologists among orthoptera, form the order dermaptera (Leach), or euplexoptera (Westwood). The spider-flies, ticks, etc, alluded to at the close of the article Diptera, form the order homa-loptera (Leach). The May flies were separated from the neuropjtera and elevated to an order trichoptera by Kirby. The thysanoptera of Haliday consist of the minute insects of the thrips tribe, generally classed with the hemip-tera; other hemiptera, as the harvest flies, plant lice, etc, have been separated by the English writers under the name of homoptera. Burmeister has separated from neuroptera those species which undergo only a partial metamorphosis into the order dictyotoptera. - Naturalists generally have been disposed to rank insects in the animal scale below mollusca, though many of their vital functions, as of locomotion and perception, indicate a superiority in the former.
Mr. Kirby and other English entomologists have accorded the precedence to insects, in opposition to Cuvier and Lamarck, who placed the mollusca first on account of their system of circulation. In the branch of articulata, the position of insects is well given by Oken, when he says that "lepidoptera are born as worms, then pass into the condition of Crustacea, and are finally developed into true insects, exemplifying the natural order of gradation of the three classes of articulata." For interesting and conclusive observations on the position that worms are the lowest, Crustacea the intermediate, and insecta the highest among articulata, see the paper by Agassiz, above alluded to, in vol. ii. of the "Smithsonian Contributions." In vol. i. of " Contributions to the Natural History of the United States," in the highest class (insecta) of articulata he establishes the three orders of my-riapods, arachnids, and insects proper, the last therefore being the highest order of the highest class, and the lepidoptera (butterflies and moths) the highest division in this order.