Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/160

 148 INSECTS HYMENOPTERA. COLEOPTERA. Gcnuina. Metamorphoses complete DlFTERA. Pupipara. (Metdbola). Aplianintera. LEPIDOPTERA. NEUROPTERA. Trichoptcra. rianipcnnia. Metamorphoses incomplete ORTHOPTERA. Pseudo-Ncuroptera. Genuina. (ffcmimctabola). HEMIPTERA. j ^optera. ( llomoptcra. No metamorphoses COLLEMBOLA. (Aberrant Insccta). THYSANURA. The obvious innovation in this arrangement is the position assigned to the Diptera, rendered necessary by the intimate relationship of Lepidoptera and Trichoptera, but in a meta- morphotic sense no particular outrage on more generally adopted systems is occasioned, and we see no alternative other than that of widely separating the two subdivisions of Neuroptera. HYMENOPTERA. In accordance with the system adopted by many modern writers, this order heads the scale as containing amongst its members those insects that appear to be endowed with the highest intellectual faculties. But at the same time it must be remembered that if the economy of the Termitidse, in the Pseudo- Neuroptera had been as fully investigated as has that of bees, wasps, and ants, it is probable that the importance of this idea might be considerably weakened. The main characteristics are as follows : Wings four (frequently absent altogether in ants, &c.), membranous, naked, transparent, with open reticulation and very few transverse nervules. Mouth mandibulate. Metamorphosis complete, but the pupa has its members free. Larva mostly apodal, but in the saw-flies much re sembling that of Lepidoptera. A convenient subdivision into three great groups is generally adopted, viz., Aculeata, Entomophaga (or Pupivora), and Phytophaga. The Aculeata may be again divided into four : Mellifcra (or Bees), Fossores (Wasps, &c. ), Hcterogynn (Ants and allies), and Tubuli- fcra (Ruby-tailed Flies), but the last is perhaps more generally con sidered as forming a special division. In these the females (and workers, when present) are provided with a sting at the apex of the abdomen, connected with a poison gland. The abdomen is petiolate. The antennae are mostly thirteen-jointed in the males and twelve- jointed in the females. In the bees the mouth parts are greatly modified, so as to form a suctorial apparatus, by the elongation of the maxilla?, labium, and lingua, the small palpi being borne at its end. The neuration of the wings is tolerably complete. The legs are much modified, according to requirements, such as pollen-gathering, burrowing, &c. The larvre are apodal, hatched in cells constructed by the parent insects, the food usually provided by them being either honey or other insects. The habits of the group are frequently social (in this case neuters or workers are present) ; many are parasitic on insects of their own group (in the broad sense), and in many instances the parasites strikingly resemble those species in the nests of which they live (as in the familiar instance of Bomlms and Apathiifi). Each division includes several families (to which we cannot allude here), and the group as a whole includes some of the most familiar insects, such as bees, wasps, and ants. The Entomophaga are invariably true parasites in the larval stage (excepting the Cynipidse), the perfect insects depositing their eggs in or on the larvre or eggs of other insects, and their larvae living upon the adipose tissue or contents of the eggs. There are no true sting and poison gland, but the female usually has the end of the abdomen provided with a long slender ovipositor, with which she can (in some cases) pierce the skin if roughly handled (but no inflammatory symptoms follow). The antennae are usually long, slender, and multiarticulate. The abdomen is strongly petiolate. The neuration of the wings is variable (often almost absent). The main divisions are Ichneumonidse, Proctotrypidss, Chalcididfe, and C//ni))itiiK, chiefly founded on the neuration, which in Chalcididx (and in a lesser degree in Proctotrypidse) is almost absent. Many members of this group are of extreme interest in consequence of tliuir economy, and especially some extremely mimite species (in Proctotrypidaz) that infest the eggs of other insects, some of which can swim by means of the wings in search of the eggs of aquatic insects. The Cynipidse, although agreeing in main point-; of structure with the other divisions, are totally different in habits, and the term Entomophaga as applied to them is erroneous (a few, however, are parasitic upon aphides). They lay their eggs in the tissues or buds of plants, and there results therefrom a swelling termed a gall, inside which the larva feeds, either solitarily, or many in one gall in separate cells. True Phytophagous Hymcnoptera (or Terebrantia) comprise 1 he two divisions known as Tenthredinidse and Siricidas. In these the abdomen, instead of being petiolate, is sessile ; the female is pro vided with a double saw in the Tcnthredinidie., and with a borer in SiricidcB. The antennae have seldom more than ten joints. The neuration of the wings is complete. The larvae differ from those of all other Hymcnoptera in possessing well-developed thoracic legs, and in addition (excepting in the Siricldse) a varying number of abdominal prolegs, and are so like those of Lepidoptera as often to require a practised eye to distinguish them therefroin. All are phytophagous, but their habits are very varied ; in fact, all the con ditions known in Lcpidoptcra are probably here present also. Some species cause galls. Some (such as the Turnip Saw-Fly) occasion great damage. The Siricidee are wood or stem borers ; the familiar Sirex gigas often appears in the midst of large towns, through the larvae or pupae having been brought in with pine timber. COLEOPTEEA. This is probably the largest, and cer tainly the best studied, of all the orders. Four-winged insects, but the upper pair of wings are modified, hard and horny in texture, and are termed &quot;elytra,&quot; lying longitudinally over the meso- and meta- thorax and abdomen, and when closed divided by a line or suture (occasionally the elytra are united, and in this case the second pair of wings is usually absent, and the insects are incapable of flight; more rarely the wings are absent altogether, both the elytra and hind-wings). Mouth mandibulate. Antenna? seldom more than 11-jointed (often much less). Metamorphosis complete ; the pupa having its members free. Larva extremely variable as to form ; usually with thoracic legs, sometimes apodal. Latreille divided the enormous amount of materials comprised in this order into four great groups according to the number of joints in the tarsi. Thus the Pentamera have five joints in all the tarsi; the Heteromera have five in the anterior and intermediate tarsi, and four in the pos terior; the Tetramera have four in all the tarsi, the Trimera three in all. More minute investigation and better know ledge have proved, however, that this system is essentially artificial, and in part founded on misapprehension ; and it is the custom amongst many modern entomologists to ignore these great divisions, and to consider the order as composed of about 75 families, without collecting them into larger groups. It would be impossible to notice here each of these families in detail, and the old system, still regarded with favour by some of our most intelligent coleop- terists as the most useful, will be followed. The general structure is so marked that but little con troversy has been occasioned. A beetle is recognized as such universally, notwithstanding the great diversity of details that exists. The only disputed elements are the Strepsiptera (Bee-parasites) and Plaiypsylla (an epizoic parasite on the beaver). The diversity in the larval con dition is much greater, and as extremes may be cited the larvae of the Staphylinidx (in which there is little difference in form and structure from those of the imago, excepting the absence of wings) and the apodal maggots of the Curculionidse. In the pupal condition this divergence mainly disappears. The Pentamera are usually considered to comprise the following superior subdivisions. Adcpluiga alone possess an inner palpiform lobe to each maxilla ; the larvae are predaceous, and feed on other insects and on flesh generally: they include the Cicindclidss (Tiger- Beetles) and CaraMdie (these two groups often termed Geodcphaga), v Inch are terrestrial, and the Dytiscidac. and Gyrinidee, familial- aquatic groups, with the addition of dmphizoa,&i anomalous Ameri can genus, recently referred to Dytiscidx. Palpicornia have short clavate antenna 1 ,, and comprise a number of small and mostly aquatic genera. Brachdytra (including Staphyttnidee,lniO wn as Rove-Beetles or Devil s Coach Horses) are known by the very short elytra (usually much shorter than the. abdomen), and form an exceedingly numerous