# 1911 Encyclopædia Britannica/Neuroptera

See also Neuroptera on Wikipedia; and our 1911 Encyclopædia Britannica disclaimer.
​NEUROPTERA (Gr. νεῦρον, a nerve, and πτερόν, a wing), a term used in zoological classification for an order of the class Hexapoda (q.v.). No ordinal name used in the class has had so many varying meanings given to it by different authors. As first used by Linnaeus (1735) it included all insects with mandibulate jaws and two pairs of net-veined wings—dragon-flies, May-flies, stone-flies, lacewing-flies and caddis-flies—and it has been employed in the same wide sense by D. Sharp (Cambridge Nat. Hist. vol. v., 1895). But detailed study of these various groups of insects shows that beneath their common superficial resemblances lie important distinctions in structure, and essential differences in the course of the life-history. Some of the families—the stone-flies, for example—have the young insect much like the adult, growing its wings visibly outside the thoracic segments, and active at all stages of its life. The dragon-flies and May-flies are also active throughout their lives and possess external wing-rudiments, though the young insects differ rather strikingly from their parents. All such families—falling into the group Exopterygota as defined in the classification of the Hexapoda—were separated from the Neuroptera by W. E. Erichson (1839) and united with the Orthoptera, with which order some entomologists still associate them under the name of “Pseudo-neuroptera.” The other groups of the old Linnean order (such as lacewing-flies and caddis-flies)—which are hatched as larvae markedly unlike the parent, develop wing-rudiments hidden under the larval cuticle, and only show the wings externally in a resting pupal stage, passing thus through a “complete” metamorphosis and falling into the sub-class Endopterygota—were retained in the order Neuroptera, which thus became much restricted in its extent. More recently the subdivision of the Linnean Neuroptera has been carried still further by the separation of the caddis-flies and scorpion-flies as distinct orders (Trichoptera and Mecaptera respectively), and by the withdrawal of the “Pseudo-neuroptera” from the Orthoptera—with whose typical families they have little in common—and their division into a number of small orders. Altogether, eight orders are recognized in the classification adopted here, the first five of these belonging to the sub-class Exopterygota and the last three to the Endopterygota (see Hexapoda).
The multiplication of orders is attended with practical difficulties, and the distinctions between the various groups of the Linnean Neuroptera are without doubt less obvious than those between the Coleoptera (beetles) and the Diptera (two-winged flies) for example. But if classification is to express relationship, it is impossible to associate in the same order families whose kinship to insects of other orders is nearer than their kinship to each other. And no student can doubt that the stone-flies are akin to Orthoptera and the caddis-flies to the Lepidoptera, while dragon-flies and May-flies stand in an isolated position with regard to all other insects. In the present article, for the sake of convenience, all the insects which have been regarded by Linnaeus and others as “Neuroptera” are included, but they are distributed into the orders agreed upon by the majority of modern observers, and short characters of these orders and their principal families are given. For further details the reader should consult the special articles on these groups, to which cross-references will be found.
Sub-class Exopterygota
Order Plecoptera.
This order was founded (1869) by F. Brauer—the name having been long previously suggested by H. Burmeister (1832)—to include the single family of the Perlidae or stone-flies. They resemble the Orthoptera more nearly than do any other group of the Linnean Neuroptera, having the anal area of the hind-wings folding fanwise beneath the costal area and the whole hind-wing covered by the fore-wing when the insect is at rest, though the forewing is not firmer in texture than the hind-wing, as is the case in the Orthoptera. In the opinion of J. H. Comstock and J. G. Needham the wing-neuration in this order is the most primitive to be found in the Hexapoda. The tenth abdominal segment carries a pair of jointed cerci which are often elongate, and the feelers are always long, while the jaws are usually feeble and membranous, though the typical parts of a mandibulate mouth are present—mandibles, maxillae with inner and outer lobes and palps, and second maxillae (labium) whose lacinae are not fused to form a ligula. Both head and trunk are somewhat flattened dorso-ventrally, giving the insects a very distinct and characteristic aspect. The stone-flies further resemble the Orthoptera in their numerous Malpighian excretory tubes, which vary in number from twenty to sixty. The reproductive organs, both ovaries and testes, become fused together in the middle of the body. A remarkable point in the Plecoptera is the presence in some forms (Pteronarcys) of small branching gills on the three thoracic and the front abdominal segments. These organs appear, however, from the observations of H. A. Hagen not to be functional in the adult insect—they are merely survivals from the aquatic nymphal stage.
Life-history and Habits.—The nymphs of the Perlidae are closely like their parents and breathe dissolved air by means of tracheal gills on the thoracic segments, for they all live in the water of streams. They feed upon weaker aquatic creatures, such as the larvae of May-flies.
The perfect insects, whose flight is feeble, are never found far from the water. A curious feature among them is the frequent reduction of the wings in the males of certain species, contrary to the usual condition among the Hexapoda, where if the sexes differ in the development of their wings it is the female which has them reduced. The Plecoptera are world-wide in their range and fossils referable to them have been described from rocks of Eocene, Miocene and Jurassic age, while C. Brongniart states that allied forms lived in the Carboniferous Period.
After C. L. Marlatt, Ent. Bull. 4 (N.S.), U.S. Dept. Agric. :
Fig. 1.—Termes flavipes, N. America. :
* 𝑎, Male from above.
* 𝑏 and 𝑐, Hind segments of male and female abdomens, showing short cerci.
* 𝑑, Male from side.
* 𝑒, Abdomen of female from side.
* 𝑓, End of shin and foot-segments.
Order Isoptera.
The two families included in this order agree with the Plecoptera in the young insect resembling the parent, but they are all terrestrial throughout life. The hind-wings have no folding anal area and the wings of both pairs, when present, are closely alike (see fig. 1) whence the name Isoptera (＝equal winged) lately applied to the group by ​G. Enderlein. The eleventh abdominal segment which carries the short jointed cerci (fig. 1, 𝑏, 𝑐) may remain in a reduced condition distinct from the tenth. There are only six or eight Malpighian tubes—contrasting with the large number of these excretory organs found in the Orthoptera and Plecoptera.
The Embiidae are feeble, somewhat soft-skinned insects with the prothorax small and the mesothorax and metathorax elongate. The feelers are long and simple, and the wings are very narrow, each with a sub-costal, a radial, a median and a cubital nervure; the branches of the median and the cubital, however, as well as the anal nervures, are vestigial, and there are a few short cross-bars between the radial and the median. Some Embiidae are entirely wingless in the adult state, and it has been suggested that this is always the condition in the female sex. According to the recent investigations of K. W. Verhoeff, the family contains only thirteen known species.
* After Marlatt, Ent. Bull. 4 (N.S.), U.S. Dept. Agric.
* Fig. 2.—Head of termite. 𝑎, Front view. 𝑏, Hind view, showing
* jaws (note the distinct inner and outer lobes of the second maxillae).
* Magnified.
The Embiidae live in warm countries, and are very retiring in their habits, hiding under stones where they spin webs formed of silk produced by glands in the basal segments of the fore-feet.
The Termitidae (so-called “white ants”) are the other family of Isoptera. They are relatively shorter and broader insects than the Embiidae with large prothorax and long wings, which have a transverse line of weakness at the base and are usually shed after the nuptial flight. The Termitidae are numerous in species in warm countries. The vast majority of individuals in a community consist of wingless forms—“workers” and “soldiers,” which are undeveloped members of either sex. Their economy is fully described in a special article on Termites.
Order Corrodentia.
The insects included in this order differ from those of the two preceding orders in their more condensed abdomens which bear no cerci, while the number of Malpighian tubes is reduced to four. In the absence of cerci the Corrodentia are more specialized than the Isoptera and Plecoptera, but some of them show a more primitive character in the retention of vestigial maxillulae—the minute pair of jaws that are found behind the mandibles in the Aptera (q.v.). A large proportion of the Corrodentia are wingless. When wings are present the front pair are much larger than the hind pair, and the neuration is remarkable for the concresence of the median with the cubital trunk, and the zigzag course of many of the branches. All the insects of this order are of small size and the cuticle is imperfectly chitinized, so that the body as a whole is soft. The name Corrodentia was first used by H. Burmeister (1832) and has reference to the biting habits of the insects. Originally, however, the Corrodentia included the order which Enderlein has recently separated as Isoptera (see above). As at present restricted, the Corrodentia include two distinct sub-orders.
After Marlatt, Bull. 4 (N.S.), Div. Ent. U.S. Dept. Agric. :
Fig. 3.—Book-louse (Atropos divinatoria, Fab.), Europe. :
| 𝑎, | From below. |
| 𝑏, | From above, (eyes, feeler, feet and claws more highly magnified). |
| 𝑐, | Second maxillae. |
| 𝑑, | Mandible. |
| 𝑒, | Lacinia or “pick” of first maxilla. |
| 𝑓, | Its palp. Highly magnified. |
Copeognatha.—This sub-ordinal name has been applied by Enderlein to the “book-lice.” These frail insects, the majority of which have wings of the type described above, are further characterized by the presence of minute but distinct maxillulae, while the inner lobe (lacinia) of the first maxilla is an elongate, hard structure (the “pick,” fig. 3, 𝑒) and the outer lobe is convex and soft. The labial (second maxillary) palps are reduced to small, rounded prominences external to the still smaller prominences that represent the lobes (fig. 3, 𝑐). The feelers of these insects are elongate and thread-like, consisting of from a dozen to nearly thirty segments. The prothorax is very small.
The book-lice are familiar wingless insects, often found in houses running about among old papers and neglected biological collections. They belong to the family Psocidae which has a few score species—most of them winged—living out of doors on the bark of trees and among vegetable refuse. In some Psocidae the wings are in a vestigial state, and the fully winged species rarely if ever fly. H. A. Hagen observed that some genera possess wing-like outgrowths on the prothorax, comparable to those seen in certain insects of the Carboniferous Period. The Psocidae themselves have not been traced back beyond the Oligocene, in the amber of which period their remains are fairly numerous.
* After Osborn, Ent. Bull. 7 (O.S.), U.S. Dept. Agric.
* Fig. 4.—Biting-louse (Trichodectes scalaris) of cattle.
Mallophaga.—This term was first applied by C. L. Nitzsch (1818) to the degraded wingless parasites (fig. 4) commonly known as bird-lice or biting-lice, differing from the true lice (see Hemiptera, Louse) by their jaws adapted for biting (not for piercing or sucking). By their structure they are evidently allied to the Copeognatha. They are abundantly distinct, however, through the short feelers with only three to five segments and the conspicuous prothorax. The head is relatively very large, but the eyes are degraded and often absent. A remarkable feature is the frequent concrescence of mesothorax and metathorax and in some cases, even, their fusion with the anterior abdominal segments. The legs are stout and spiny, and well adapted for clinging to the hair or feathers of the host animal. It is usual to divide the Mallophaga into two families—the Liotheidae, possessing labial palps and two foot-claws, being fairly active insects, which are capable, on the death of their host, of seeking another, and the Philopteridae, without labial palps and with a single foot-claw modified for clasping (fig. 4) which never leave the host and perish themselves soon after its death.
Order Ephemeroptera.
This order includes the single family of the Ephemeridae or May-flies. The name, although quite recently proposed by A. E. Shipley, should be used rather than A. S. Packard’s older term Plectoptera on account of the great liability of confusion between the latter and Plecoptera. The May-flies are remarkably primitive in certain of their characters, notably the elongate cerci, the paired, entirely mesodermal genital ducts, and the occurrence of an ecdysis after the acquisition of functional wings. On the other hand, the reduced feelers, the numerous Malpighian tubes (40), the large complex eyes, the vestigial condition of the jaws, the excessive size of the fore-wings as compared with the hind-wings and their complex neuration with an enormous number of cross-nervules are all specializations. So in some respects is the life-history, with a true larval preparatory stage, unlike the parent form, and living an aquatic life, breathing dissolved air by means of a paired series of abdominal tracheal gills. Except for its aquatic adaptations, however, the ephemerid larva is wonderfully thysanuran in character, and possesses conspicuous and distinct maxillulae. See special article on May-flies.
Order Odonata.
The distinctness of the dragon-flies from other insects included in Linnaeus’s Neuroptera was long ago recognized by J. C. Fabricius, who proposed for them the ordinal name of Odonata (1775). They resemble the May-flies in their “hemimetabolous” life-history; the young insects are markedly unlike their parents, inhabiting fresh water and breathing dissolved air, either through tracheal gills at the tip of the abdomen, or by a branching system of air-tubes on the walls of the rectum into which water is periodically admitted. The winged insects resemble the May-flies in their short feelers and in the large number (50 to 60) of their Malpighian tubes, but differ most strikingly from those insects in their strong well-armoured bodies, their powerful jaws adapted for a predaceous manner of life, and the close similarity of the hind-wings to the fore-wings. All the wings are of firm, glassy texture, and very complex in their neuration; a remarkable and unique feature is that a branch of the radius (the radial sector) crosses the median nervure, while, by the development of multitudinous cross-nervules, the wing-area becomes divided into an immense number of small areolets. The tenth abdominal segment carries strong, unjointed cerci, while the presence of reproductive armature on the second abdominal segment ​of the male is a character found in no other order of the Hexapoda. See special Dragon-fly.
Sub-class Endopterygota
Order Neuroptera.
The insects retained in the order Neuroptera as restricted by modern systematists are distinguished from the preceding orders by the presence of a resting pupal stage in the life-history, so that a “complete metamorphosis” is undergone. Structurally the Neuroptera are distinguished by elongate feelers, a large, free prothorax, a labium with the inner lobes of the second maxillae fused together to form a median ligula, membranous, net-veined wings without hairy covering, those of the two pairs being usually alike, the absence of abdominal cerci, and the presence of six or eight Malpighian tubes. The larvae are active and well-armoured, upon the whole of the “campodeiform” type, but destitute of cerci; they are predaceous in habit, usually with slender, sickle-shaped mandibles, wherewith they pierce various insects so as to suck their juices. The order contains nine families, most of which are wide in their geographical distribution. Fossil Neuroptera occur in the Lias and even in the Trias if the relationships of certain larvae have been correctly surmised.
The Sialidae or alder-flies (q.v.) differ from other Neuroptera in the jaws of the larva—which is aquatic, breathing by paired, jointed abdominal gills—resembling those of the imago, and being adapted for the mastication of solid food. Some American genera (Corydalis) which belong to this family are gigantic among insects and their males possess enormous mandibles. The Raphidiidae or snake-flies (q.v.) are remarkable for the long, narrow, tapering prothorax which gives the appearance of a constricted neck, while the female has a long ovipositor. Both these families are very sparingly represented in our fauna.
The Myrmeleonidae are large insects with short clubbed feelers on their prominent heads, and two pairs of closely similar net-veined wings, with regular oblong areolets at the tips. Their predaceous, suctorial larvae are the well-known ant-lions (q.v.). No members of this family inhabit our islands, though a few species occur in neighbouring parts of the continent. The same is the case with the allied Ascalaphidae, which are distinguished from the Myrmeleonidae by their elongate feelers—as long as the body—and by the irregular apical areolets of the wings. The curious Nemopteridae have slender feelers and very long strap-shaped hind-wings. The Mantispidae are remarkable among the Neuroptera for their elongate prothorax, raptorial fore-legs and hypermetamorphic life-history, the young campodeiform larva becoming transformed into a fat cruciform grub parasitic on young spiders or wasp-larvae (see Mantis-fly). The last-named two families are confined to warm regions of the earth. The lacewing-flies (q.v.), however, of which there are two families, the Hemerobiidae and Chrysopidae, whose larvae feed on Aphids, sucking their juices, are represented in our fauna. So are the tiny Coniopterygidae, which are covered with a white powdery secretion, and have very small hind-wings. Their larvae resemble those of the lacewings, attacking scale-insects and sucking their juices.
Order Mecaptera.
This small order was founded (1869) by F. Brauer—under the name of Panorpata—for the small family of the Panorpidae or scorpion-flies (q.v.). The name Mecaptera is due to Packard. They may be distinguished from the Neuroptera by the elongation of the head into a beak, the small prothorax, the narrow, elongate wings with predominantly longitudinal neuration, the presence of abdominal cerci and the cruciform larva. They are generally but sparingly distributed over the earth's surface and can be traced back in time to the early Jurassic epoch.
Order Trichoptera.
The caddis-flies (q.v.) constitute this order, the name of which (suggested by H. Burmeister) indicates the hairy covering of the wings. They are abundantly distinct from the Neuroptera and Mecaptera, through the absence of mandibles in the imago, the maxillae—both pairs of which possess the typical inner and outer lobes and jointed palps—forming a suctorial apparatus. The feelers are long, slender and many-jointed. While the fore-wings are elongate and narrow, the hind-wings are broad, with a folding anal area. At the base of each wing projects a dorsal lobe—the jugum—and the neuration is predominantly longitudinal, resembling so closely that of the lower Lepidoptera (q.v.) that a nearer relationship of the Trichoptera to that order than to any group of the old Linnean Neuroptera is certain. Fossil Trichoptera occur in rocks of Liassic age.
Frequently the whole of the Trichoptera are included in a single family, but most special students of the order recognize seven families. In all Trichoptera the maxillary palps of the female are five-segmented. The family Phryganeidae have males with four-segmented hairy palps; the larvae inhabit stagnant water and make cases of vegetable fragments. In the Limnephilidae the maxillary palp is three-segmented in the male, the larvae are variable in habit, many forming cases of snail-shells. The males of the Sericostomatidae have two or three segmented palps; their larvae inhabit running water and make cases of grains of sand, or of small stones. In the Leptoceridae, Hydropsychidae, Rhyacophilidae and Hydroptilidae the palps of the males have five segments like those of the females. The stone-built cases of the carnivorous Hydropsychid larvae are familiar objects in the water of swift streams.
Bibliography.—For a general account of the various orders mentioned in the present article see D. Sharp, Cambridge Natural History, v. (London, 1895); L. C. Miall, Nat. Hist. Aquatic Insects (London, 1895); J. G. Needham, &c., Aquatic Insects in New York State (Albany, N.Y., 1903); F. Brauer, Die Neuropteren Europas (Wien, 1876); J. A. Palmén, Zur Morphologie des Tracheensystems (Leipzig, 1877). Noteworthy writings on the special orders are: Plecoptera: F. J. Pictet, Histoire naturelle des insectes Neuroptères-Perlides (Génève, 1871–1872); A. Imhof, Beiträge zur Anatomie von Perla maxima (Aarau, 1881); K. J. Morton, Trans. Ent. Soc. Lond. (1894–1896). Isoptera: For Embiidae see H. A. Hagen, Canadian Entom. xvii. (1885); G. Enderlein, Zool. Anz. xxvi. (1903); K. W. Verhoeff, Abhandl. K. Leopold. Carolin. Akad. lxxxii. (1904). For Termitidae see Termites. Corrodentia: For Copeognatha see G. Enderlein, Ann. Hist. Nat. Mus. Nat. Hungar, i. (1903), and Zool. Jahrb. Syst. xviii. (1903); R. McLachlan, “British Species” in Ent. Mo. Mag. iii. (1867). For Mallophaga see E. Piaget, Les Pediculines (Leiden, 1880–1885); F. Grosse, Zeits. wiss. Zoolog. xlii. (1885). For Ephemeroptera and Odonata, see May-fly and Dragon-fly. Neuroptera (sens. str.): H. A. Hagen, Proc. Boston, Nat. Hist. Soc. xv. (1873); F. Brauer, Verh. Zool. bot. Gesells. Wien, xix. (1869); R. McLachlan, “British Neuroptera Planipennia” in Trans. Entom. Soc. (1868). Mecaptera: F. Brauer (loc. cit.). Trichoptera: R. McLachlan, Trichoptera of the European Fauna (London, 1874–1880), and “British Trichoptera” in Trans. Entom. Soc. (1865 and 1882); R. Lucas, Arch. f. Naturg. lix. (1893); G. Ulmer, Abhandl. naturhist. Verein Hamburg, xviii. (1903); A. Thienemann, Zoolog. Jahrb. System, xxii. (1905).  (G. H. C.)