The apparatus has been described as resembling the piston or plunger of a force-pump, which moves to and fro within a cavity inside the insect's body, and by that means draws in and forces out the water. The tail is defended by a sort of coronet, composed of five hard bristle-like pieces, which are under the control of the creature, and may be opened and closed at pleasure. The larva appears capable of inflicting a somewhat painful pinch by this contrivance, so that, what with its wonderful mask, with its powerful squirt, and with its tail thus armed, it would be difficult to select another insect better prepared for battle with creatures of every aquatic tribe than it. The action of the pumping apparatus sends it rapidly forward through the water, somewhat like a paddle-wheel, or at least upon the same principle as that contrivance, namely, the resistance offered by the water to the stroke of this apparatus. CHAPTER V. MEANS OF DEFENCE OF THE LARVA. There is, perhaps, no period in the life of an insect when it is so much in danger of the attacks of foes, as when it is in the larva state. Possessed, at the best, with but very feeble powers of locomotion, in comparison with those of winged insects, it is continually exposed to destruction on all sides, from which it has not the power to escape. Not only do insects of various species particularly select the larva for the object of their attacks, but birds and other creatures are also in the lists against them. Thus imperilled, what chance has the larva against foes so numerous, and in a contest so unequal? It has been calculated that a pair of sparrows, for their own consumption, and for that of their tender brood, destroy at least three thousand caterpillars in a week! and we well know what multitudes of larvæ fall into the clutches of the cawing rooks which follow the tail of the plough. The winged insects are tolerably secure, although many even of their ranks fall victims to the swift-winged swallow and sand-martin, and to the rapid leap of the artful trout. But the poor crawling larvæ are neither strong enough to fight, nor swift enough to flee, and fall by thousands into the unsparing hands of their various enemies. [Illustration: _Leaf-rolling Larvæ._] [Illustration: _Larva Case of Shells._]