More Minor Horrors

by Sir A. E. Shipley

Fig. 27.—Stegomyia fasciata. Above, the larvae; below, the eggs. Both natural size.

The mosquito in question belongs to the species Stegomyia calopus (Blanchard), or, as it is more often called in English textbooks, Stegomyia fasciata (Fabricius). The genus Stegomyia differs from other Culicidae in having a dark grey or black colour, whilst the Culicidae are as a rule browner. Stegomyia also has silver-white spots and silver glistening scales, especially on the back of the legs and on the abdomen. The grown-up mosquito is comparatively small, and very elegant. Its length is some 3 to 4 mm., but if the mouth parts be added is some 6 to 6½ mm. long. As is usual, the male is smaller and feebler than the female. When settled—as, for instance, whilst sucking the blood of its host—it rests upon its first four legs only, the two hindmost being stretched out abaft like pennants waving in the air; but in general it has the hump-backed appearance of Culex and not the straight outline of Anopheles. The colour is greyish black, modified by numerous white spots and rings. There is a white rim round the eyes, and a very characteristic lyre-like pattern on the dorsal surface of the thorax. The structure of the mouth parts is much the same as that of any other Culicidae. The antennae have fourteen joints, the last two of which in the male are longer than the others. As is again usual, the antennae of the male have long brush-like hairs, organs by means of which they find the female. The legs are banded alternately with white and black rings. It is this character, indeed, which has given this mosquito the name of the ‘tiger-gnat.’ The wings are very iridescent.

Fig. 28.—Larva of Stegomyia fasciata breathing on the surface of the water. Highly magnified.

The pupa of Stegomyia is darker and blacker than that of Culex, and, seen from the side, the head and the thorax are somewhat more triangular than the same parts in Culex. As the pupa grows older it grows darker. The length of the larva is 4 to 6 mm., somewhat larger than that of the gnat. But, like that, it has a respiratory-tube stretching out from the last segment of the abdomen, almost at right angles to the rest of the body. This respiratory-tube is much shorter than that of Culex, but is long enough to enable the larva to hang obliquely down into the water. The eggs are very large. They are covered by a mass of small ‘cells’ containing air, and they never tend to form a conglomerate mass like those of Culex, but are laid singly, and remain isolated until the larvae hatch. After floating a certain time they usually sink to the bottom of the water. Their length may be about a millimetre, and their colour is almost black. When the egg hatches, the anterior third of the shell splits off and the larva at once emerges.

As is so often the case with mosquitos, it is the female alone which bites. The male nourishes itself on plant-juices, saps, and so on—especially they like sugary secretions—and in the absence of blood the female is reduced to a similar diet. Hence Stegomyia is comparatively common in dwellings where sweetstuffs are—bakeries, sugar-refineries, and so on. These mosquitos are, like the cockroach, the fly, and the bed-bug, inhabitants of human dwellings. They are indeed domesticated, and are always to be found in the neighbourhood of human houses or buildings or ships, and are very rarely indeed found far away from the sphere of man’s activities.

Fig. 29.—Egg of Stegomyia fasciata (highly magnified). Notice the air-‘cells.’.

They are very apt to bite one in the neck, creeping along the darker parts of the clothing until an unprotected region of the body is reached. Unless one has very thick socks they frequently bite the ankle, and they are as tireless in their pesterings as ever Mrs. Pardiggle was—no sooner are they driven away than they return to the attack. The bite is painful, and in many people raises a considerable swelling.

The Stegomyia bite not only during the night, but also during the day. According to R. O. and O. Neumann—in Brazil, at any rate—they are capable of biting not only during the twilight, but at any times. The bite lasts twenty to thirty seconds, after which the mosquito rests a bit, waving its third pair of legs in the sun. After this rest she flies away to some sheltered spot, and whilst blood is being digested the mosquito takes nothing but water—a very proper dietetic measure. After three or four days the female is ready for another meal.