Fig. 59.—Red Water Mite (nat. size, and under surface magnified).
‘This spot or particle induced me to consider with more attention this minute and hitherto unregarded insect, and even to undertake the dissection of it. But who would imagine that on this examination it should prove a perfect and surprising insect? This is, however, a certain fact; and thus in that infinite variety of works, by means of which God is pleased to make Himself known to us, we ever meet with new matter of admiration and astonishment.
‘This little creature being extracted from the shell that covered it, looks like a young spider before it has left its egg. On the fore part is the head (Fig. 43D, a) and on its head are the eyes, b: under the eyes are placed its little legs elegantly coiled and folded, c c; but they appear much more distinctly on turning the insect on its back, d d; and in this situation also it best appears with what art these legs are laid up in the shell, and all are covered with hair. The colour of this little creature is, as I have already observed, a mean between that of vermilion and purple; and this colour shows itself through the coat or shell, which is transparent. I cannot determine to what species of insects this is to be referred; nor can I say to what size it grows, or by what kind of creature it is thus deposited on the Water Scorpion in the form of an egg, there to receive life and growth. Nevertheless, I cannot but look on the discovery I have made as very interesting, since it proves that there are in the nature of things eggs which acquire a sensible growth by an entraneous nourishment, unless perhaps some naturalist should choose to consider this as a complete insect, rather than as an egg; nor shall I strenuously oppose his opinion, seeing that, in all cases, the egg is in reality no other than the insect itself, which remains in that state till it has acquired sufficient strength to break its prison, and live without such a covering[35].’
Having quoted Swammerdam, let us see what De Geer has to say on the subject:—
‘On the body and legs of many aquatic insects, such as Dytiscus and Water Scorpions, may be frequently seen little oval, seed-like bodies, of a bright red colour, firmly attached, and, as it were, implanted in the skin, by a little stalk. I have had Water Scorpions with the upper surface so covered with these red bodies that there was scarcely a vacant space on the skin. They are most frequently to be seen in the spring; but the insects on which there was such a great number did not live long with me. Having crushed some of these seed-like bodies, I found them filled with red liquid matter. I am convinced, by experiment, that they are the eggs of Water Mites, since there came out of them little red Mites with round bodies and long legs, which swam about with great swiftness.
‘These red Water Mites, then, attach their eggs to the bodies and legs of larger aquatic insects, and there they remain till the young are hatched. And since we find eggs of many different sizes, we may be sure that they grow and increase in size, doubtless owing to a certain nutritive juice which passes from the body of the insect into the egg. Hence it is, as I have seen myself, that Water Scorpions loaded with these eggs become weak and feeble, because they are obliged to furnish their hangers-on with nourishment from their own bodies. Moreover, these eggs appear to cause the Water Scorpions some irritation or uneasiness, since I have often seen them rub with their feet those parts of the body where the eggs were; and perhaps they did this with the view of rubbing them off, but they were too securely fastened[36].’
Dugès watched the development of the common Red Water Mite (Fig. 59), and tells us that towards the end of May the females deposit their eggs in the leaves of pondweed, which they puncture with their beaks. The larva (Fig. 60), red in colour, with six legs, is free-swimming, and has a large beak, which looks like a great head, and terminates in a narrow mouth. It is not known how long this larval stage continues; but in the next stage (Fig. 61) the Mite becomes parasitic on aquatic beetles and bugs, fastening its beak into the body of its host, from which it derives its nourishment. The legs and palps are often retracted or absorbed, so that it is not difficult to understand how it was Swammerdam and De Geer took these parasitic nymphs to be the eggs of the Mite. During their parasitic condition they increase considerably in size, at last emerging as adult eight-legged free-swimming Mites. It was just before the emergence of the Mite that Swammerdam examined the parasitic nymph, for he figures the ‘insect,’ which he extracted from the egg, as having eight legs (Fig. 43D).
Fig. 60.—Larva of Water Mite.
