1, A), are usually convex above, with straight hind margins (dorsa); when the elytra are closed, the two hind margins come together along the mid-dorsal line of the body, forming a suture.
In many beetles the hindwings are reduced to mere vestiges useless for flight, or are altogether absent, and in such cases the two elytra are often fused together at the suture; thus organs originally intended for flight have been transformed into an armour-like covering for the beetle's hind-body.
The identification of the elytra of beetles with the fore-wings of other insects has indeed been questioned (1880) by F.
Meinert, who endeavoured to compare them with the tegulae of Hymenoptera, but the older view was securely established by the demonstration in pupal elytra by J.
Tower (1903), of nervures similar to those of the hind-wing, and by the proof that the small membranous structures present beneath the elytra of certain beetles, believed by Meinert to represent the whole of the true fore-wings, are in reality only the alulae.
The tergite of the prothorax (pronotum) is prominent in all beetles, reaching back to the bases of the elytra and forming a substantial shield for the front part of the body.
The hard fore-wings (elytra) are strengthened with marginal ridges, usually inflected ventrally to form epipleura which fit accurately along the edges of the abdomen.
The beetles are ovoid in shape, with smooth contours, and the elytra fit over the edges of the abdomen so as to enclose a supply of air, available for use when the insect remains under water.
In many Carabidae the hind-wings are reduced or absent, and the elytra fused together along the suture.
The pronotum and elytra are often adorned with bright colours or metallic lustre, and marked with stripes or spots.
12) with very hard cuticle and somewhat abbreviated elytra, with over 2000 species, most of which live on decaying matter, and FIG.
The prothorax is convex in front, and is usually drawn out behind into a prominent process on either side, while the elytra are elongate and tapering.
19), and exhibit magnificent metallic colours; their elytra are used as ornaments in human dress.
When Hydrophilus dives it carries a supply of air between the elytra and the dorsal surface of the abdomen, while air is FIG.
24), insects with rather soft cuticle, the elytra (often abbreviated) not fitting closely to the sides of the abdomen, the head constricted behind the eyes to form FIG.
The Rhipidophoridae are beetles with short elytra, the feelers pectinate in the malesandserrate in the females.
The males are very small, free-flying insects with the prothorax, mesothorax and elytra greatly reduced, the latter appearing as little, twisted strips, while the metathorax is relatively large, with its wings broad and capable of longitudinal folding.
I and 25) have the terminal antennal segments pectinate, and so arranged that the comb-like part of the feeler cannot be curled up, while the elytra completely cover the abdomen.
Most of the Chrysomelidae are metallic in colour and convex in form; in some the head is concealed beneath the prothorax, and the so-called "tortoise" beetles (Cassidinae) have the elytra raised into a prominent median ridge.
The wings of Coleoptera (including the elytra) are described and discussed by F.
When wings are present, the fore-wings are small firm elytra, beneath which the delicate hind-wings are complexly folded.
Fore-wings modified into firm elytra, beneath which the membranous hind-wings (when present) can be folded.
The front wings of the wasp have a conspicuous white patch near the tip and a patch similar in size and colour is present on the wings of the beetle, which, unlike the majority of beetles, habitually keeps its wings extended, and since the elytra are exceptionally short the wings are not covered by them when folded.
The elytra are equally reduced, and apparently for the same purpose, in an Australian Longicorn beetle (Esthesis ferrugineus), which, like so many wasp-like Hymenoptera, has the body banded red and black.
In the European Longicorn (Clytus arietis), on the other hand, the elytra are of normal length and are banded with yellow stripes.
The mimicry of these insects therefore is synaposematic; but some, at all events, of the flies like the Bombylid Exoprosopa umbrosa, probably form pseudaposematic elements in the group. Into another category Hymenoptera enter not as models but as mimics, the models being inedible Malacodermatous beetles mostly belonging to the genus Lycus and characterized by orange coloration set off by a large black patch upon the posterior end of the elytra and a smaller black spot upon the thorax.
It has been shown by means of spectroscopic observations that the green colour of the elytra, &c., is due to the presence of chlorophyll; and that the variations of the spectral bands are sufficient, after the lapse of many years, to indicate with some certainty the kind of leaves on which the insects were feeding shortly before they were killed.
It is true that in beetles and certain other insects there are the elytra or wing cases - thin, light, horny structures inclined FIG.
The elytra, however, are comparatively long narrow structures which occupy a position in front of the wings, of which they may be regarded as forming the anterior parts.
The elytra are to the delicate wings of some insects what the thick anterior margins are to stronger wings.
The elytra, moreover, are not wholly passive structures.
The elytra serve as protectors to the wings when the wings are folded upon the back of the insect, and as they are extended on either side of the body more or less horizontally when the insect is flying they contribute to flight indirectly, in virtue of their being carried forward by the body in motion.
They are then known as elytra, from the Gr.
The elytra are very hard, and in some cases fused with one another, rendering flight impossible.
Of cantharidin has been obtained from different samples; and it has been ascertained that the elytra or wing-sheaths of the insect, which alone are used in pharmacy, contain more of the active principle than the soft parts taken together; but apparently cantharidin is most abundant in the eggs and generative organs.