Fig. 37.—Larva and Pupa of Earwig.
In working over these insects, the forceps, or pincers, at the end of the abdomen will attract attention. They are found throughout the family, but little is known of their function. It is said that they are used to aid in folding the wings, and tucking them under the wing-covers. This can scarcely be their only function, for they are found in species that have no wings. Probably they serve as organs of defence and, to some slight extent, of offence. When the abdomen is curled up, these forceps certainly give the insect a threatening appearance. They cannot, however, do much harm.
These forceps differ in shape in the male (Fig. 38) and female, the blades being almost close together in the latter. In the males they differ considerably in size. Of 583 mature males taken in one day in the Farne Islands, and examined by Messrs. Bateson and Brindley, the forceps varied in length from 2·5 mm. to 9 mm.[24] These are called respectively ‘low’ males and ‘high’ males. The latter are in all points larger than the former, and have been described as a separate species, ‘but it was impossible to get reliable measurements of the total length, owing to the fact that the abdominal segments telescope into each other’ (cf. p. 30).
After examining the antennae and dissecting out the mouth organs, the peculiar overlapping or imbrication of the plates of the abdomen should be looked for; and on the membrane that connects them the spiracles may be detected.
The wings and the complex method of folding have led some systematists to rank the Earwigs as an Order, while some others rank them as a Sub-order. For the present, at any rate, we need not concern ourselves about this. It is enough for us to know that they are closely related to the Orthop´tera.
As we look at the Earwig from above, the wing-cases recall to our mind those of the Devil’s Coach Horse (Fig. 31), though there is one great difference. From beneath those of the Earwig project two small leathery pieces which are absent in the Beetle. These pieces are not, as one might imagine, at the tips of the wings, but on the front margin, about halfway down, and is indicated in the illustration by the shading between the extremity of the wing-case and the crease-mark at a.
Fig. 38.—Earwig (male).
From the illustration we may understand how the Earwig opens and closes its wings. From the point a veins, which are thickened about halfway down, radiate to the hinder edge of the wing, and a little beyond the thickening they are connected by a vein which runs parallel with the hinder edge. These radiating veins are brought together, so that there is a fan-like closing, like that of the Cockroach, but from a different centre. The wing is then folded back at the place where the veins are thickened, and then there is a second transverse fold at the point a, so that the only part of the wing now visible is the leathery patch, which projects beyond the wing-case when the wing is tucked away.