Orthoptera with the hind legs differing from the others by being more elongate and having their femora broader near the base. Antennae short, with less than 30 joints. No exserted ovipositor in female. Tarsi short, with three distinct joints. The auditory organ placed on the side of the upper part of the first abdominal segment.
Fig. 165.—Tryxalis nasuta, female. Natural size. Europe.
We commence the consideration of the saltatorial Orthoptera with the family Acridiidae. It includes the grasshoppers of our native fields as well as the destructive migratory locusts of foreign countries, and is the most numerous in species and individuals of any of the Orthopterous families. Our native grasshoppers, though of small size, give a very good idea of the Acridiidae. Active little Insects, with large head, conspicuous eyes, laterally somewhat compressed body, long hind legs with femur directed upwards and backwards, the knee-joint forming an acute angle, the organs of flight pressed to the sides of the body, our common grasshoppers represent the Acridiidae quite as truly as do the gigantic exotic forms, some of which measure 9 or 10 inches across the expanded wings.
Fig. 166.—Front of head of Porthetis sp. Transvaal.
The large head is immersed behind in the thorax; the front is deflexed, or even inflexed, so as to be placed in a plane at an acute angle with that of the vertex (Fig. 165); the compound eyes are placed at the sides of the head and rather widely separated; in front there are three small ocelli. Two of these are placed one on each side close to the eye between the eye and the base of the antenna; the third ocellus being in the middle just in front of the insertion of the antennae, between the edges of the margined space that usually runs down the middle of the front. The positions of these ocelli and the shape of the front and upper parts of the head are of importance in the classification of the family; the ocelli vary much in their development, being in some species beautifully clear and prominent (Fig. 166), while in others they are small, not easily detected, apparently functionally imperfect. The antennae are never very long, are sometimes compressed and pendent from the front of the head. The parts of the mouth are very large. The prothorax is much arched; it is often carinate or crested along the middle of the notum; this part is frequently prolonged backwards, forming a sort of hood over the base of the wings; the surface may be rugged or warty, forming in some species inexplicable structures; the legs are widely separated, all of them being placed at the sides of the body; the edge of the pronotum is distinct and situate close to the base of the leg; the prosternum frequently bears a large projection extending directly downwards between the front legs. The mesothorax is short, its chief sternal piece is very broad, the middle legs being very widely separated. The metathorax is larger; its sternal plate usually exhibits behind a sort of embrasure filled up by a portion of the first ventral plate.
Fig. 167.—Alar organs of Acridiidae (Bryodema tuberculata). A, Left tegmen; B, left wing: ar.med, area mediastina; ar.sc, area scapularis; ar.disc, area discoidalis; ar.an, anal area; v.m, vena mediastina; v.r, vena radialis; v.r.a, vena radialis anterior; v.r.m, vena radialis media; v.r.p, vena radialis posterior; v.i, vena intercalata; v.u.a, vena ulnaris anterior; v.u.p, vena ulnaris posterior; v.d, vena dividens; v.pl, vena plicata. (After Brunner.)
The hind body is elongate, and shows distinctly eight dorsal segments, behind which are the pieces forming—in the female, the fossorial organs which replace an ovipositor—in the male, the modified parts connected with the terminal segment. The alar organs (Fig. 167) exhibit, according to Brunner, the same areas as we have described in Blattidae. According, however, to Redtenbacher[[210]] the tegmina of the Acridiidae and other saltatorial Orthoptera differ from those of the cursorial group (with the exception of the Phasmidae) in that they possess a praecostal field, due to the fact that the vein which in the Cursoria is costal, i.e. forms the front margin, in the Saltatoria lies, on the contrary, in the field of the wing. If this view be correct the mediastinal area of Brunner is not homologous in the two divisions. The tegmina are long and comparatively narrow; they are of firm parchment-like texture, with several longitudinal veins, which divide beyond the middle, so as to become more numerous as they reach the extremity of the wing; there is much reticulation, dividing the surface into numerous small cells. The hind wings are much more ample, and of more delicate texture; the longitudinal veins fork but little, the numerous cross veinlets are fine. In repose the hind wings fold together in a fan-like manner, and are entirely concealed by the upper wings. The front and middle legs are similar and small, the coxae are quite small, and do not completely fill the articular cavities, which are partly covered by membrane; all the tarsi are three-jointed. The basal joint, when looked at beneath, is seen to bear three successively placed pads, so that from beneath the tarsi look as if they were five-jointed (Fig. 185, C). The hind legs are occasionally very long; their femora, thicker towards the base, are generally peculiarly sculptured, bearing longitudinal ridges or grooves, which are more or less spinose, and are also very frequently marked with short parallel lines meeting a central longitudinal line at similar angles, so as to give rise to a well-marked pattern; where the legs are broader the pattern is more complex (Fig. 168). The long tibiae bear two rows of spines on their upper or posterior edge; this part of the hind leg can be completely bent in under the femur. The stigmata consist of one prothoracic, one metathoracic, and eight abdominal pairs.