Page:A note on grappling tail-hooks in anopheline larvae - M.O.T. Iyengar - 1922.pdf/7

632 Giles; maculatus, Theob; minimus, Theob.; ''funestus var. listoni, Liston; stephensi, Liston; barbirostris, v. d. Wulp; hyrcanus, Pallas and gigas'', Giles. In all these species, the hooks are present quite characteristically.

In a pond, it may be presumed that if the larva were to be disturbed it would be compelled to go to the bottom. But this has never been observed to happen. The larvæ of Anophelines breeding in ponds with a floating vegetation of Pistia stratiotes for instance, get in between the roots of the Pistia when disturbed and hang from the rootlets by their tail-hooks. But sometimes they grip the rootlets with their mandibles. From such positions it is difficult to dislodge them. If the larvæ should go to the bottom of the pond on any disturbance, the possible dangers they would risk thereby would be (1) the exposure to enemies like fish and (2) exposure to pressure at the depths of a pond which cannot be withstood by these air-breathing organisms. This also enlightens us as to why larvæ always rest near floating aquatic plants or algal scums, or near the edge of the pond or cistern, and never at the clear centre of a pond.

Above we have seen the utility of the tail-hooks in stagnant waters. In flowing waters, the larvæ of species breeding therein stick to boulders on the sides of the streams by means of their well-developed tail-hooks. The larvæ of A. maculatus and minimus breeding in the 'jhoras' (hill-streams at the foot of the Himalayas) have been observed to do so. But the power to stick to the sides of streams is particularly remarkable with larvæ of A. maculatus, and they are able to withstand very strong currents. Experiments in the Bengal Duars have shown that flushing a stream has no great effect in driving the larvæ of A. maculutus far down the stream. When the stream gets a good flush, the maculatus larvæ breeding in it at once get to the surface of the flush water, move a short distance with the current and suddenly dart out to the sides and there stick to the stones or boulders, in spite of the strong current. When the flush spends itself and the level of the water falls, the larvæ creep down the sides, and when the water is stationary again, get into the water. The larvæ of A. culicifacies breeding in the sluggish streams in the colliery districts also utilise their tail-hooks to stick to stones and sand,