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Nature and Art, Vol. VIII, No 1, June 1900

<h3>SOME WATER INSECTS.</h3> CHARLES C. ADAMS. IN field and forest bright-colored and active insects attract our attention. Aquatic insects, on the other hand, do not, as a rule, possess such bright colors as their land relatives nor move about with as great rapidity, yet it does not follow that they are less interesting. As would be expected, some of the most interesting things about these animals are connected with modifications of their form which have resulted from their aquatic life. It is believed that the ancestors of water insects have been land insects which invaded the water and have thus become greatly modified in their new surroundings. Locomotion and breathing, either one or both of these functions, are, as a rule, very different in land and water insects. The variety of aquatic insects, if we consider only the adults, is not great when compared with the land insects. But when we compare fresh and salt water forms it is surprising how few kinds there are which live in the sea, in spite of its vast area and great food supply. So few are the insects found in the sea, or other salt waters, that, to most of us, to speak of aquatic insects only calls to mind fresh water forms. We shall, therefore, refer almost wholly to fresh water forms. Let us consider briefly a few examples of these. We may distinguish two general groups, according to their special habitat. Belonging to the first group are those insects which frequent, primarily, the surface of the water. These forms which breathe air directly, and not air dissolved in water, as is the case with many other water insects, must be kept dry and be able to maintain their position on the surface of the water. Surface insects, such as the Water-Skaters, found on quiet ponds and streams, and their marine relatives, Holobates, accomplish this by means of fine hairs which cover the feet where they touch the water. The same physical principal is involved here, as when a needle or wire is floated upon water,—that of surface tension. The fine hairs on the body of a water insect act in the same way as those on the feet, and thus keep the insect dry when below the surface. These insects are thus able to breathe as land insects, on account of their being on the surface, and consequently their respiratory systems are not as greatly modified as in many of the insects living beneath the surface. It must be borne in mind that an insect breathes by means of the air which enters the body by small openings and is led by means of tubes, which become very finely divided, like veins, to all parts of the body. By means of contractions and expansions of the body of the insect, the air within these tubes is caused to circulate, and thus impure air is driven out and a fresh supply is pumped in. Two of the commonest of these surface dwellers, so well known to the small boy who frequents ponds and streams, are the Whirligig-beetles or Lucky-bugs, and the long-legged Water-striders or Water-skaters. The Whirligig-beetles are easy to recognize on account of their characteristic circular gyrations when disturbed, and by their habit of associating in large numbers in quiet places. When one of these, groups is disturbed they exhibit such activity that they well deserve their name, "Crazy-bugs." The eyes of these beetles [Pg 26] are very peculiar in that each eye is divided into an upper and lower part. Thus the insect has practically an upper and lower pair, one adapted for sight at the surface, and the other for vision under water. The Whirligigs do not seem to be very particular about their food, as they will accept both live and dead insects which fall into the water, and even under some circumstances will feed upon plants. 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. The Water-skaters, or Striders, prefer quiet waters, as do the Whirligigs, but do not have the decided social disposition, shown in the latter to such a marked degree. These Skaters, on account of their long legs and short bodies, are the "Daddy long-legs" of the water. These characteristics and their habitat make them easy to recognize. They are nervous, active insects in their movements, jumping and skimming about on the surface with but little show of grace and ease as compared with the ordinary graceful curves of the whirligigs. Their food habits are very similar to those of other surface insects, that is, dead and dying insects found floating on the water. But their method of taking food is quite different from that of the Whirligigs, because of the great difference in the structure of their mouth parts. The Whirligig, being a beetle, has the typical biting mouth parts, while the Strider has a slender beak or proboscis, by means of which it sucks the juices from its prey, as do other bugs. The fore legs are used to seize the prey and bring it within reach of the beak. The middle and hind pair are used for rowing over the surface, the latter pair, primarily, for steerage, the fine hairs on the legs making it possible, as mentioned before, to make use of the surface tension. Large dimples are formed on the surface of the water where the feet touch it. One would hardly expect it possible for an insect standing on the surface of water to get its feet dirty, yet the great care which they give to cleaning their feet clearly shows that dirt is of common occurrence, even there. The white or gray color on the lower side of the body is due to the reflection of light from minute hairs which cover the surface, and keep the insect dry even when submerged. The marine relatives of our Striders have some curious habits. Some of them live out at sea, hundreds of miles from land, where they are thought to feed upon the dead bodies of small animals. When the surface of the sea is calm they glide in colonies quickly over the surface, showing great skill in diving, but if the sea begins to become agitated they immediately disappear from the surface. Perhaps the most remarkable habit which a surface insect has is that possessed by some of the allies of the Skaters, which not only swim in the water, but actually run on the under side of the surface film. It would be very interesting to know how such a habit was acquired. Another interesting group of insects are those which breathe air, as the surface film insects, yet seek their food below the surface. These insects are compelled, on account of their air-breathing habits, to repeatedly visit the surface or communicate in some way with a fresh supply of air. <table class="sp2 mc w50" title="INSECTS."> <tbody> <tr> <td colspan="3"> <ANTIMG style="width:100%" src="images/i_058.jpg" alt="" /> </td> </tr> <tr> <td class="xx-smaller ac w30">FROM COL. CHI. ACAD. SCIENCES.</td> <td class="x-smaller ac w40">INSECTS. Life-size.</td> <td class="xx-smaller ac w30">COPYRIGHT 1900, BY A. W. MUMFORD, CHICAGO.</td> </tr> <tr> <td class="xx-smaller ac w30">Archimerus calcarator</td> <td class="x-smaller ac w40">Nezara hilaris</td> <td class="xx-smaller ac w30">Metapodeus femoratus</td> </tr> <tr> <td class="xx-smaller ac w30">Oncopeltus fasciatus</td> <td class="x-smaller ac w40">Leptoglossus phyllopus</td> <td class="xx-smaller ac w30">Conorhinus sanguisugus</td> </tr> <tr> <td class="xx-smaller ac w30">Ranatra fusca</td> <td class="x-smaller ac w40">Benacus griseus</td> <td class="xx-smaller ac w30">Cicada septemdecim</td> </tr> <tr> <td class="xx-smaller ac w30">Galgulus oculatus</td> <td class="x-smaller ac w40">Zelus bilobus</td> <td class="xx-smaller ac w30">Platycotis sagittata.</td> </tr> </tbody> </table> We have two families of the large-sized water beetles, common in our ponds and streams. The Predaceous water-beetles and the Water-scavenger beetles. These are easily recognized, because in the former, the antennæ are thread-like and not enlarged at the tip. While the members of the Water-scavenger family have the antennæ enlarged or club-shaped at the tip. The Predaceous water-beetles are often quite common under electric lights, where they have been attracted by the intense light. Their large size and clumsy movements, when out of water, attract attention. But when seen in water their skill as swimmers is in striking contrast to their awkward movements made on land. The hind legs are flattened and very powerful, the surface being increased by a fringe of [Pg 29] strong hairs on the inner side. In swimming the stroke is made by both legs at once. Perhaps the most interesting facts about these beetles are those associated with their method of breathing. The horny wing cases covering the abdomen are very thick and fit close against the abdomen, except at the extreme posterior end of the body. The space between the wing cases and the upper surface of the abdomen forms a large air space. The spiracles, or openings into the respiratory system, are situated at the margins of the upper side of the abdomen. When the beetle comes to the surface for a fresh supply of air it exposes the tip of the body and then by a depression of the tip of the abdomen allows a fresh supply of air to enter into the cavity below the wing covers; this cavity is then closed and the beetle is ready for another trip under the water. When resting in the water they float with their head downward and the end of the abdomen slightly projecting from the water; thus a fresh supply of air is easy to secure. In their food habits these beetles are predaceous, and in addition to other insects, will even kill small fish. The Water-scavenger beetles are not such perfect swimmers as the Predaceous ones. When the latter makes a stroke in swimming it strikes with both hind legs, while the Scavengers strike alternatingly with the hind legs. Their method of securing and carrying air, as with other water-beetles, is remarkable. In addition to the air reservoir under the wings, they have on the under side of the body large hairy areas which communicate with the one under the wings. All the air spaces are thus in direct communication. 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. The long antenna which is folded backward and reaches to the rear part of the head, occupies an air space in its apical half, and in addition is covered by fine hairs, thus being doubly protected from being wetted. At the moment the beetle reaches the surface, by a stroke of the antenna (on the side which is nearest the surface, the body being tilted), the film from the air space in which the antenna rests is carried upward and outward to the surface of the water, thus forming an opening to the exterior. By movements of the wings, aided by bellows-like contractions and expansions of the body, a fresh supply of air is pumped into the air reservoir. In speaking of peculiar water insects one must not forget to mention the larva of Donacia. The adult female of this interesting leaf-eating beetle often cuts circular holes in the large leaves of water-lilies, and then deposits her eggs at the margin of these holes on the under side. When the larvæ hatch they make their way to the roots, upon which they feed. The really remarkable thing about this larva is how it gets its air supply, as it does not have gills, nor is it known to visit the surface for a fresh supply of air, and yet it has a normal air-breathing system. On the dorsal surface, near the tail end of the body, are two slender, curved, spine-like processes. The air tubes of the body arise from the base of these spines, and spiracular-like openings are found at their base. Two different views have been advocated to explain how it is possible for the larva to secure air. There seems to be no difference of opinion with regard to the source of the air supply, from the air cells in the root of the plant upon which the larva feeds. One view is that these air spaces in the plant are punctured by the spines and thus the air is taken directly into the air tubes. The other view is that the larva bites a hole into the air space and then, by the aid of the spines, holds the openings at the base of the spine against the air space and thus the air is taken up. The Back-swimmers are curious little fellows which swim upside down in the water, and by means of their sucking mouth parts, prey upon other small animals. The lightness of their bodies and the large amount of air which they carry with them make it necessary when they wish to remain below the surface to hold [Pg 30] fast to some object. Thus it takes constant effort in order to remain below the surface. For this reason it is quite natural that they should very often be found floating at the surface where no effort is needed to maintain their position and where an abundant supply of air is accessible. Another method of securing fresh air, but differing from that of any of the insects previously mentioned, is by means of elongated breathing tubes, thus allowing the insect to remain submerged and yet secure a fresh supply of air from the surface. This method is used by some predaceous water bugs, as shown in the plate, Ranatra fusca. As with all of our Predaceous water bugs, which have the elongated respiratory tube at the end of the body, the Water-scorpion has its fore legs adapted for capturing and holding its prey, which consists generally of small fish and insects. The apical part of the fore leg folds back on the basal part which is grooved on its inner face, as a knife blade folds into its handle. As the slender legs of this bug would indicate, it is not an active swimmer, but crawls about slowly. Doubtless the best known, to most people, of this type of breather, are the Giant water bugs, which accumulate in such large numbers under and in the globes of electric lights. The paired nature of the breathing tube is well shown in the plate. These bugs are powerful swimmers, as is shown by their flattened hind legs. Even young fish are not overlooked by these voracious bugs. A South American kind is much larger than our species, reaching from four to four and one-half inches in length, or about twice the size of our species. The shortness of the air tube suggests that this organ is not used in just the same manner as in the Water-scorpions, and the areas of fine hairs on the under side of the body suggest that these insects may be somewhat of a compromise between those insects which carry air below with them and those which remain submerged, except for the tube which communicates with the air. Most of the insects previously mentioned are ones which throughout life live in water, but a very large number are aquatic only during their larval or immature stages. The Mosquito is a good illustration, of this type. In some of its habits the Mosquito is well known, but this is primarily due to the biting habit of the female. The researches of recent years clearly show that the annoyance from the bite itself, is, in the case of some kinds of Mosquitoes, only a small part of the mischief that they can do. The life history of the Mosquito has been summarized somewhat as follows by Dr. L. O. Howard: The eggs are laid at night, in a boat-shaped mass containing from two hundred to four hundred eggs. These may hatch in 16 hours, the larval stage lasting about a week, and the pupal stage about 24 hours. Thus the entire cycle may be completed in 10 days, under favorable circumstances, but may be greatly delayed by a low temperature. The rapidity with which the complete cycle may be passed through makes it possible for a very large number of broods to occur during a single season. The Wigglers or Wiggle-tails, often so numerous in rain-barrels, are the larvæ of mosquitoes. Every one has noticed that these larvæ when not disturbed rest at the surface, but when frightened drop slowly downward in the water, since they are heavier than this medium, yet they rest at the surface, by means of a rosette of thin plates at the tail end of the body. These act as the hairs on the legs of the Water-strider, and make use of the tension of the surface film which holds the larva up, as the surface tension held up the Water-strider. On the next to the last segment of the Wiggler there is a large breathing tube which reaches to the surface when the larva is floating. The food of the larva is said to be decaying vegetable matter. The short pupal period is also passed floating, but it now has two breathing tubes near the points of attachment of the wings. When ready to transform it crawls out onto the pupal skin and dries its wings preparatory to flight. Our common mosquitoes belong to three genera, Culex, Anopheles and Corethra. The annoyance caused by the irritation resulting from the bite is not understood, as no poison gland has been found. The females only of our mosquitoes are known to suck blood. From researches made during the past few years [Pg 31] it is now definitely known that the bite of certain kinds of mosquitoes is really dangerous. This is not on account of the actual puncture made by the insect, but due to the presence of the germs of malaria, which are introduced into the wound from the infected insect. The only mosquitoes which are definitely known to transmit this malarial parasite to man belong to the genus Anopheles. The malarial parasite thus has two hosts, mosquitoes belonging to the genus Anopheles and man. This parasite infests the stomach walls of the mosquito, where it rapidly multiplies and becomes mature; then escaping from this locality, accumulates in the salivary glands. From this reservoir they are easily transferred to their human host at the time of sucking blood. These aquatic insects which we have discussed so briefly are only a few samples from a very large number whose history and habits are full of interest to those who find the study of animal life a fascinating subject. <hr> <div style="break-after:column;"></div>

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