Fig. 184.—Xiphocera (Hoplolopha) asina. S. Africa. (After de Saussure.)
The tribe Pamphagides[[236]] includes some 200 species, found chiefly in Africa and the arid regions near the Mediterranean Sea. They are mostly apterous forms, and this circumstance has, according to de Saussure, exercised a marked influence on the geographical distribution of the species. Although the tribe consists chiefly of apterous forms, several species possess well-developed wings; sometimes this is the case of the male but not of the female. Some of the species are highly modified for a desert life, and exhibit a great variation in the colour of the individuals in conformity with the tint of the soil they inhabit. Xiphocera asina (Fig. 184) is thought by Péringuey to be the prey of the extraordinary South African tiger-beetles of the genus Manticora.
We have already mentioned the tribe Oedipodides[[237]] as including most of the species of migratory locusts of the Old World. Some striking cases of variation in colour occur amongst the winged Oedipodides. In certain species the hind wings may be either blue or rosaceous in colour; it is thought that the latter is the tint natural in the species, and that it is due to the mixture of a red pigment with the pale blue colour of the wing; hence the blue-coloured wings are analogous to cases of albinism. But the most remarkable fact is that this colour difference is correlative with locality. Brunner von Wattenwyl says[[238]] that the blue variety of Oe. variabilis occurs only in a few localities in Europe—he mentions Vienna and Sarepta,—and that where it occurs not a single red example can be met with. Similar phenomena occur in other species in both Europe and North America, and L. Bruner has suggested[[239]] that the phenomena in the latter country are correlative with climatic conditions.
The group Eremobiens, a subdivision of Oedipodides, includes some of the most interesting forms of Acridiidae. Its members have several modes of stridulation. Cuculligera flexuosa and other of the winged forms, according to Pantel,[[240]] produce sounds by the friction of the middle tibia against the wing, both of these parts being specially modified for the purpose in the male sex. The most peculiar members of the Eremobiens are some very large Insects, modified to an extraordinary extent for a sedentary life in deserts and arid places. Trimen says[[241]] that a South African species, Trachypetra bufo, which lives amongst stones, is so coloured that he had much difficulty in detecting it, and that he noticed in certain spots, often only a few square yards in extent, where the stones lying on the ground were darker, lighter, or more mottled than usual, that the individuals of the grasshopper were of a similar colour to the stones.
Fig. 185.—Methone anderssoni, female. S. Africa. a, Front of head; b, posterior leg; c, d, front and hind feet. (c and d magnified, the others natural size.)
The Insect referred to by Trimen is, we believe, the Batrachotettix whiti of de Saussure. In this species the alar organs are completely absent, and the pronotum forms a sort of hood that protects the base of the hind body. Some of the desert Eremobiens vary so much that the differences found among individuals of the same species are said by Brunner and de Saussure to be so great as to affect even the generic characters, and give rise to the idea of an "uncompleted species-formation."
Fig. 186.—Portions of middle of the body and hind leg of Methone anderssoni ♂: a, femur; b, an inferior fold; c, rattling-plate; d, striated surface; e, the adjoining sculpture; f, grooved portion of tegmen. The part e is really, like d, a portion of the second abdominal segment, not of the third, as might be supposed from the figure.
Methone anderssoni, an inhabitant of the Karoo Desert of South Africa, is one of the largest of the Acridiidae. A female of this species is represented of the natural size in Fig. 185. This Insect is remarkable on account of the complex organs for producing sound, and for the great modification of the posterior legs (Fig. 185, b), which do not possess locomotive functions, but serve as a portion of the sound-producing apparatus, and as organs for protecting the sides of the body. This Insect is said to be very efficient in making a noise. The sexes differ considerably in their sound-producing organs, a portion of which are present in the female as well as in the male (Fig. 186). Connected with the first abdominal segment, but extending backwards on the second, there is a peculiar swelling bearing two or three strongly raised chitinous folds (Fig. 186, c). When the leg is rotated these folds are struck by some peg-like projections situate on the inner face of the base of the femur, and a considerable noise is thus produced. The pegs cannot be seen in our figure. This apparatus is equally well developed in female and male. On the second abdominal segment, immediately behind the creaking folds we have described, there is a prominent area, densely and finely striated (Fig. 186, d): this is rubbed by some fine asperities on the inner part of the femur near its base. Sound is produced by this friction on the striated surface, the sculpture of which is abruptly contrasted with that of the contiguous parts: these structures seem to be somewhat better developed in the male than they are in the female, and to be phonetic, at any rate in the former sex. The male has the rudimentary tegmina (Fig. 186, f) much longer than they are in the female (Fig. 185), and their prolonged part is deeply grooved, so as to give rise to strong ridges, over which plays the edge of the denticulate and serrate femur. There is nothing to correspond to this in the female, and friction over the surface of this part of the male produces a different and louder sound. There can be little doubt that this is a phonetic structure peculiar to the male. It approximates in situation to the sound-producing apparatus of the males of the Stenobothri and other Acridiidae. Methone anderssoni has large tympanal organs: the small tegmina cover them up completely. In the female the tips of the tegmina seem to be adapted for forming covering-flaps for the tympana. In both sexes there is a sac (Fig. 186, b) adjoining the structures we have mentioned, but which is not directly phonetic, though it may be an adjunct of the apparatus.