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Neuroptera
1911 Encyclopedia Britannica
or (Gr. veupov, a nerve, and 7rmEp6v, a wing), a term used in zoological classification for an order of the class Hexapoda. 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 wingrudiments, 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 Hexapodawere 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 " Pseudoneuroptera." 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 Endopterygotawere 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 forewing 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 Mayflies.
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.
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 After C. L. Marlatt, Ent. Bull. 4 (N.S.), U.S. Dept. Agric. FIG. 1. - Termes flavipes, N. America.
a, Male from above. Mag- b and c, Hind segments of male and nified 6 times. female abdomens, showing short d, Male from side. cerci; magnified 24 times.
e, Abdomen of female from f, End of shin and foot-segments magniside. Magnified 4 times. fled 40 times.
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 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 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.
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. 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 After Marlatt, Bull. 4 (N.S.), Div. Ent. U.S. Dept. Agric. FIG. 3. - Book-louse (Atropos divinatoria, Fab.), Europe.
a, From below. c, Second maxillae.
b, From above, magnified 30 d, Mandible.
times (eyes, feeler, feet and e, Lacinia or " pick " of first claws more highly magnimaxilla.
fled). f, Its palp. Highly magnified. 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.
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.
Mallophaga
This term was first applied by C. L. Nitzsch (1818) to the degraded wingless parasites (fig. 4) commonly known as birdlice 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 After Osborn, Ent. Bull. 7 the Ephemeridae or May-flies. The name, (OS.), U.S. Dept. Agric. although quite recently proposed by A. FIG. 4. - Biting-louse E. Shipley, should be used rather than (Trichodectes scalaris) of A. S. Packard's older term Plectoptera on cattle. Magnified 30 account of the great liability of confusion times.
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 crossnervules are all specializations. So in some respects is the lifehistory, 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.
