Fig. 64.—The Earwig (Forficula auricularia).
What dress is to man, their wings are to insects; by these we distinguish them, at the first glance, from one another. The elytra,—those horny sheaths which protect the membranous wings,—embrace, in the Coleoptera, the entire upper surface of the long annulated abdomen, and resemble vari-coloured chlamydes. But now, look for the elytra of our Forficula. You will hardly believe that they are represented by this kind of abbreviated light-brown jacket, which does not extend below the middle of the back. Do you observe yonder whitish spots? They indicate the tips of the wings, which are longer than their covers. Lift up one of the elytra with your penknife, and you will find that the wing which it partly screens is worth your attention. The fore part (we should call it the upper, if the animal walked erect like a man) is straight, and without a fold. Raise it with a pin to see the posterior or lower part. Observe, it curves underneath so as to bind the intermediate portion like a fan. But this flabelliform wing,—of tolerable dimensions when unfolded,—seems intended by the Creative Thought only to mark its unity of plan: the earwig does not fly,—it secures its food by crawling.
The elytra and the wings, inconspicuous as they are, produced so great an impression on the early naturalists, that they made them the principal characteristics of an entire order of insects. De Geer, a celebrated Swedish naturalist, named them the Dermaptera (from δέρμα, skin, and πτερόν, wing), in allusion to the transparent skin-like appearance of the elytra. This name, though adopted by Kirby, has not been preserved. A French entomologist suggested the designation which is now in use,—Orthoptera (from ὀρθός, straight, and πτερόν),—referring to the manner in which the wings are folded underneath the elytra.
Here we must pause to recapitulate for the benefit of our younger readers, and to avoid confusion, the various orders into which the insect world is divided.
1. Aptera (from α, without, and πτερόν, a wing),—wingless. Examples—Flea, louse, chigo.
2. Diptera (δίς, two, and πτερόν),—two-winged. Sub-divided into Nemocera, having six-jointed antennæ; Brachycera, having three-jointed antennæ. Examples—Gnat, tipula; May-fly, gad-fly.
3. Hemiptera (ἕμι, half, and πτερόν),—half-winged. Sub-divided into Heteroptera, with wings of different textures; Homoptera, with wings of one substance. Examples—Land-bug, water-bug; cicada, lantern-fly.
4. Lepidoptera (λεπίς, a scale, and πτερόν),—scaly-winged. Examples—Tiger-moth, butterfly, silkworm.
5. Orthoptera (ὀρθός, straight, and πτερόν),—straight-winged. Examples—Earwig, cockroach, locust.
6. Stymenoptera (ὑμήν, a membrane, and πτερόν),—membranous-winged. Examples—Bee, wasp, ant.