An aquarium of the kind described stands at present on my writing-table. Many have been the inquiries as to what kind of creature lived therein; and more than one old hand at collecting has failed to find the insect. It is always safe to look round the sides of the basin for the breathing-tube; if it is not detected in this situation, a glance along the surface of the tiny pools will probably show a break in the film. The Water Scorpion will not be far off.
That the insect really does cover itself with mud may be demonstrated by transferring it from the aquarium described to any shallow vessel, and allowing a fine stream of water—say, from a dipping-tube—to fall gently on it. The mud will be washed away, and in a few seconds will settle at the bottom.
It is well to keep such an aquarium covered, for the Water Scorpion has no mean power of flight. A circular plate of glass, which may be bought for a few pence, makes the best cover, but a piece of fine muslin fastened round the rim of the basin will do. Swammerdam says, ‘These Water Scorpions live all the day in the water, out of which they rise about the dusk of evening into the air, and so flying from place to place, often betake themselves in quest of food to other waters.’ Then follows a deduction which shows how far he was in advance of his time: ‘This affords us a satisfactory reason for the great number of insects that immediately appear in the smallest collections of water, since they may very well get thither when it is dark, so that the opinion which ascribes to putrefaction the power of forming insects, &c., must, by this instance of the Water Scorpion’s nocturnal transmigrations, appear more and more frivolous and unnecessary.’
Fig. 43.—A. Water Scorpion. a, rostrum; b, wing-cases; c, wings; d d, second and third pairs of legs; e, raptorial legs (the first pair); f, spine forming breathing-tube; g, parasitic mite. B. Portion of an oviduct containing eggs (magnified). C. An egg (magnified). D. Parasitic mite. a, head; b, eyes; c, legs; d d, legs (seen from under surface). (After Swammerdam.)
No larva or other animal that is of any value should be kept in the same aquarium with the Water Scorpion. Dr. Hill, who annotated the English edition of Swammerdam, says, ‘There is not perhaps in all the animal creation so outrageous or fierce a creature against those weaker than itself as the Water Scorpion. It destroys, like the wolf among sheep, twenty times as many as its hunger requires.’ The Rev. G. C. Bateman placed one in a saucer with a tiny minnow; ‘but no sooner did the little fish swim within reach of the fore-legs of the scorpion than it was seized by them, and pressed against the hungry creature’s rostrum.’ It seems to be particularly fond of Asellus, the water woodlouse. I have often taken dead specimens of this crustacean, sucked completely dry, from between the raptorial legs of the insect. One specimen was so thoroughly cleaned out that it was mounted just as it was, the only preparation being a brief soaking in spirit.
In examining the head the eyes may be readily distinguished, and on pressing the rostrum or beak with a needle, the proboscis will be forced out, just as one may force out the sting by pressing the abdomen of a bee or a wasp. In this group the antennae are three-jointed and concealed. When one begins to look for these organs he will probably come to the conclusion that the concealment is highly effectual.
A very simple method of finding them in a spirit specimen is to take the insect between the thumb and index finger of the left hand, holding it up to the light in such fashion as to keep the first pair of legs well clear of the head. Then, with a needle held in the right hand, raise the thorax till it lies in the same plane as the body. Each antenna lies in a groove beneath the eye. Gentle manipulation with the needle will lift them out, so that they may be clearly seen, not only with the hand magnifier, but with the unassisted eye. Or the insect may be pinned down under water instead of being held in the hand, and the antennae lifted or brushed out of the groove.
It will greatly simplify matters if, before attempting to raise the wings, the fact is borne in mind that the tip of the right wing-case lies over that of the left. It is perhaps as well to remove the wing-case altogether by inserting a needle under it, and gently raising it, using a little pressure in an outward direction. It will then be quite time to raise the wing and to see the method of folding and unfolding.
