Water beetle

“ Although so very different in general appearance to the preceding insects, this beetle will be found on careful examination to agree with them in all important respects, being only what a ground beetle might naturally become if forced to lead an aquatic existence. Breathing is effected in all the water beetles by the spiracles of the abdomen, which alone are developed. The air is taken in between the elytra and the body, and owing to the convexity of the former, a supply can be retained sufficient to last the insect some twenty or thirty minutes. ”

“ The huge Hercules Beetle of South America has been seen to carry off his mate bodily in this way. Other tropical beetles have specially developed forelegs for grasping their spouse, should she prove coy and attempt playfully to run away.
Water-beetles (Ditiscus marginalis) are carnivorous types which have become adapted to life in freshwater, although the adults have not lost the power of flight. In our native great water-beetle the large hind legs are fringed with bristles, and serve as oars, while air can be stored under the wing-covers. There is only a partial metamorphosis. ”

“ Yet the advantage of the plumed seeds no doubt stands in the closest relation to the land being already thickly clothed with other plants; so that the seeds may be widely distributed and fall on unoccupied ground. In the water-beetle, the structure of its legs, so well adapted for diving, allows it to compete with other aquatic insects, to hunt for its own prey, and to escape serving as prey to other animals. ”

“ Then more brown objects, larvae of dragon-flies and water-beetles, detach themselves from the stems of the plants and cruise up and down seeking what they may devour. Other creatures feeding and swimming among or beneath the plants crawl out on to the upper surface, and the water-beetles come up to breathe, or to play upon the surface. One of the largest of these is a very fine black beetle, a vegetable-feeding creature. It is most interesting to see two of them--they generally live in pairs--browsing on one of the fern-like plants of the Thames. ”

“ The respiratory openings in the Predaceous water-beetles open on the upper side of the abdomen, but in these beetles they are on the lower side and surrounded by short hairs which preserve the air film on the lower surface. When the fresh air supply has been exhausted the beetle comes to the surface, tips the body slightly, so as to bring the region on one side of the body just behind the head, to the surface. ”

“ In the larva of the water-beetle mentioned a few lines above, a circular membrane is stretched over the valves, ornamented with concentric zones of different colours, and having a circular aperture in the centre, (Pl. III. fig. 8.) Other peculiarities presented by these pneumatic orifices are to be found in species belonging to the different orders.
Many aquatic insects have a special provision for introducing the air more readily into their system, which is rendered necessary by the difficulty they would experience in bringing their spiracles into contact with it. ”

“ AN APPARENT SINGULARITY ACCOUNTED FOR.
It is generally well known that birds are very active agents in the extension of vegetation, and that fruit and flowers are, to a great extent, rendered prolific by the insects which visit their blossoms; but few people are aware of the means through which fish are formed in lakes and ponds, which are not connected with other waters. Here, also, an insect is the principal agent. The large water-beetle, which is in the habit of feeding upon the spawn of fish, occasionally in the evening climbs up the stems of rushes, &c. ”

“ That oval beetle which is swimming on its back, and using two legs like oars, is the water boatman. It fastens on to the head of small fish, and soon kills them. It lives in the water, but if put on land it can fly. Look at that brute crawling over the mud, with its lobster-like head. It has sharp claws and a hollow snout. It lies in wait for its victims, and when it seizes them it sucks the juice out of them with its beak. It looks only of a dull brown now, but when its wings are expanded its [167] body is of a blood red colour, and its tail is forked. ”

“ By this means any Beetles in the weed will be dislodged from their hiding-places, and fall down into the bottle.
They have, in confinement, the same habit of making a snug place for themselves; and more than once I have fancied that a Beetle of this species had escaped from the aquarium, when all the time it was hidden in a thick patch of water-moss. They are practically vegetable [50] feeders, though Dallas says that they are not such strict vegetarians as to deny themselves a meal of animal food when they meet with a dead mollusc or larva in the course of their wanderings. ”

“ May-flies, the white ants and numerous other insects have, like the locust, an incomplete metamorphosis, that is, the young when hatched resemble in most respects, except in the absence of wings, their parents.
The adult water-scavenger beetle feeds chiefly on decaying vegetation in the water, but instances of the taking of other insects and of snails have been noted. Although an aquatic insect the beetle, like its larva, has no gills for breathing the air which is mixed with the water, but has to come to the surface occasionally to obtain air. ”

“ When a beetle plunges beneath the surface, as he often does when frightened, he carries down a small bubble of air between the ends of his horny wings and the tip of his body. On account of his body being lighter than water it takes some effort to dive, but none to rise to the surface. The two hind pairs of legs which are used so much in swimming are very much flattened and plate like, making excellent paddles, as is shown by their exceedingly rapid movements. ”

“ One often seen is about an inch long, and is deep black in color, with a narrow band of violet running round the outer edge of its wing-cases. This, too, is a creature of prey. It cannot hurt you; but if you pick it up it will make your fingers smell very nasty. For it can pour out from its mouth a drop or two of a dark-brown liquid which has a horrible odor.
Then there are a good many beetles which live in streams and ponds, and are called water-beetles in consequence. They can swim and dive very well, and are also able to fly. Almost every night they go for long journeys through the air. ”

“ The grub of the Great Water Beetle spends all his time (three or four years, too, I expect) in {96} the water, and I think he feeds on decaying plants, but I am not sure of this. Some people say that the Stag-beetle uses his great antlers to crush twigs and leaves so as to get the juice. This may be so, but I have never seen him do it.
The Musk Beetle
Who has a very nice smell
Another big and beautiful insect is the Musk Beetle. ”

“ Every few minutes they come to the surface and lift their wings to get a little air under them, then down they go into the brook. They are very hungry beetles, eating other insects which they find in the water. The boldest often try to take a bite out of a fish. Just think of calling a baby beetle a water-tiger! Well, these babies are as savage and ferocious to the little creatures living about them in the water as a big tiger would be to us, if we should happen to meet one. ”

“ The water-beetles, of which there are many species, remain in the water all day, but toward evening come upon the ground and fly about, then plunge themselves again in the water at the approach of the rising sun. The larvæ of these insects are entirely aquatic, but when the time of their pupa state arrives, they take to the earth, where they make a spherical case; so that these insects are aquatic in the larva, terrestrial in the pupa, and amphibious in the imago state. ”

“ I have often kept specimens of these larvæ in vessels of water and noticed their predaceous habits; they feed on the larvæ of other water insects, but are not able to destroy fish, not being furnished with jaws or bodies nearly so strong as the perfect insect itself possesses. When the larva wishes to turn into its pupa state, it makes a round hole in the bank of the pond it inhabits, and there undergoes its change, turning into a full-grown beetle in about three [Pg 31] weeks' time. ”

“ My glass pond was at first occupied by a dozen Water-beetles, whose diving performances are so curious to watch. One day, meaning no harm and for want of a better place to put them, I fling among them a couple of handfuls of Caddis-worms. Blunderer that I am, what have I done! The pirate Water-beetles, hiding in the rugged corners of the rockwork, at once perceive the windfall. They rise to the surface with great strokes of their oars; they hasten and fling themselves upon the crowd of carpenter Caddis-worms. ”

“ If the insect is a beetle, it may be plunged into boiling water, or into spirits of wine, in which a very little corrosive sublimate has been dissolved. Both modes will destroy the life rapidly, but the former is the better of the two. When walking in the fields or woods, a wide-mouthed, strong bottle, about half full of spirits of wine, is a useful auxiliary, as all kinds of beetles, and even flies and bees, can be put into it ”

“ In this water, not only the common potamogetons and confervas, or pond-weeds and water-mosses are found growing in an healthy state, but numbers of small black water beetles are seen swimming about, which die on being taken out and plunged suddenly into cold water. ”

“ But here a very natural question arises as to what, if not the natural fly, the fish takes the imitation to be? In a communication to the Field in June, 1897, I described, under the heading of “A New Trout Fly,” the imitations of two Corixæ. This seems to be a key to the whole [Pg 89] question. The number of insects living in fresh waters, and possessing the power of moving through it, is enormous.
There are between 220 and 230 different species of Water Beetles in our waters. There are also very many different sorts of Heteroptera, including the numerous family Notonectidæ. ”

“ Touching at some islands, we sailed to Bahia, and from thence to Rio, where I have already been some weeks. My collections go on admirably in almost every branch. As for insects, I trust I shall send a host of undescribed species to England. I believe they have no small ones in the collections, and here this morning I have taken minute Hydropori, Noterus, Colymbetes, Hydrophilus, Hydrobius, Gromius, etc., etc., as specimens of fresh-water beetles. I am entirely occupied with land animals, as the beach is only sand. ”

“ The Water-beetles, for instance, which must be able to lurk concealed among the weeds, &c., until a victim comes within their reach, and then to pursue and overtake it, carry down with them a supply of air in a kind of reservoir, situated between the body and the wing-cases. ”

“ H.W. Bates communicated a paper by Mr. D. Sharp on the respiratory function of the Carnivorous Water Beetles (Dytiscidæ) . Experiments made by the author on numerous species show that there are wide differences in the length of time they spend submerged and on the surface for breathing purposes. Most specimens of the group are more active by night than by day. ”

“ Water beetles, backswimmers, water boatmen, and many other creatures move about more or less freely in the water, propelling themselves along with jerky movements. Suspended between surface and bottom are the zooplankton, the tiny water fleas, cyclops, daphnia, and others, which feed by filtering minute algae. ”

“ At night some of the whirligig beetles, the shiny, bean-like creatures seen whirling in incessant circles in corners by the bank, make a quite audible and almost musical sound upon the water. The activity of many of the water insects is astonishing. Besides keeping in almost incessant motion, those which spend most of their time below water have generally to come up constantly to breathe. Such are the water-bugs, water-scorpions and stick insects, which, though slender as rushes, and with limbs like hairs, can catch and kill the fry of the smaller fishes. ”

“ But insects are, for the most part, chiefly terrestrial, feeding upon terrestrial plants, at least in their full-grown condition; though a large number of these animals are fluviatile, and even some marine, during their earlier periods of life. In the Vertebrata, the adaptations are more diversified. Only one class of these animals is entirely aquatic—the fishes; and the number of the marine species is far greater than that of the fresh-water kinds. Among reptiles there are many which are aquatic, either throughout life, or through the earlier period of their existence. ”

“ But it is advisable in connection with our present subject to dwell especially on some insects that remain continually under water till they are ready to undergo their final moult and attain the winged state, which they pass entirely in the air. The preparatory instars of such insects are aquatic; the adult instar is aerial. All may-flies, dragon-flies, and caddis-flies, many beetles and two-winged flies, and a few moths thus divide their life-story between the water and the air. ”

“ The first which we shall notice is the insect which, from its singular resemblance to a boat propelled by a pair of oars, has received the popular name of Water-boatman. Its scientific name is Notonecta glauca, the meaning of which we shall presently see. It belongs to the order of Heteroptera, and is one of a numerous group, all bearing some resemblance to each other in form, and being almost identical in habits. Though they can fly well, and walk tolerably, they pass the greater part of their existence in the water, in which element they find their food. ”