The locust plague and its suppression / by Æneas Munro.

  • Munro, Aeneas.
Date:
[1899]
Catalogue details

Licence: Public Domain Mark

Credit: The locust plague and its suppression / by Æneas Munro. Source: Wellcome Collection.

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    membrane, and it is liable to be distended, and thus it may vary in length and thickness at one time as compared with another. The length of the migratory locust may then be put down as a general rule from 2^ to 3 in., or 63 to 75 millimetres, and about § of an inch in thickness in the abdomen. The chest or trunk is thicker or larger—^ an inch, or 1.0 to 12 millimetres—and has a square shape. The North American and Cyprian locusts are smaller, but the South American is practically the same in these respects as those found in Africa. 94. Wings.—The wings extend beyond the extreme tip of the abdomen by about J an inch, and sometimes even f of an inch. The wings are not soft and velvety like those of a butterfly, but rather resemble in material silica quartz or thin mother-of-pearl, and seem almost weather-proof. The exterior pair of wings, which more or less overlap the other pair, generally have a greenish or grey tinge, and are covered with a series of blackish-brown or brown markings or stripes, many of which are in the form of parallelograms, and sometimes in certain species little squares or specks, as seen in Fig. 4, a and b. The back pair of wings—rather more delicate in structure and larger—are rather triangular-shaped, and are probably more serviceable for flight than the fore wings; and when in a quiescent state, they are folded up fan-fashion by about twenty folds, and these extend (beneath the forward or upper pair) beyond the farther point of the abdomen as indicated. The exterior or forward wings are the longest, and the other pair fold themselves under their protection. 95. The ear.—Behind the wings and in the first segment of the abdomen may be seen the auditory membrane, which indeed performs the functions of an ear. The characteristic sound or noise, “ cri-cri,” from which the name “ cricket ” is derived, is produced by rubbing the femur of the back pair of legs upon the wings. The male is supposed to produce this more than the female, and it is perhaps most observable in the period when the hoppers are beginning to fly. 96. Respiration.—The breathing is carried on by openings in the various rings of the body, each of which leads into a respiratory tube (spiracle), which we may call a trachea. This tube extends its rami- fications all over the body, terminating in a series of sacs or air chambers capable of expansion and contraction, so as to assist in long and high flights. The arrangement or mechanism whereby this tube is worked is not unlike in principle that of a spiral wire introduced into an indiarubber gas tube. There is a spiral thickening on the inside of the trachea (composed of chitine) which keeps its sides from collapsing. These tracheal or bronchial spiracles are always open. When locusts take high flights, continuing their flights for days and nights together, as no doubt they do, e.g. on sea, and sometimes they go as high as two miles, it will at once be apparent how important this
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