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MAN'S BEST FRIENDS IN THE INSECT WORLD
The primary object in adding these studies to this book, is to introduce the reader to another of Nature's creatures, a formidable enemy of the mosquito, which, could we enlist it in our campaigns, would make possible a 24-hour-a-day war by its natural enemies against that most baneful of creatures. As we have learned, we have, in the nocturnal twelve hours, a powerful ally against the night variety of mosquitoes. We have also a powerful ally for the diurnal twelve hours against the day variety, if we but study its habits, and cause it to be of service to us. This ally is known as the Dragon Fly, the Mosquito Hawk, or the Devil's Darning Needle. To realize that this service can be effected, we have but to contemplate to what a high state of cultivation man has brought one of Nature's wild insects, the honey bee.
That the propagation of the Dragon Fly will involve the hardest kind of work, and will often meet with dismal and disheartening failures, goes without saying; but the labor involved will not be as hard as the bat work was, because, dealing with a daylight creature, the studies can be carried on during the day, while the bat work had to be done principally at night.
SUGGESTED OCCUPATION FOR WOMEN
As our American women are more and more creditably filling important roles in every-day affairs, it has occurred to the author, that, if some lady enthusiast, desiring to be of real value to her fellow-beings and to do something fundamentally different from women's ordinary pursuits, would take up this work, she would find an ideal out-door recreation in an unexplored field; in fact the daintiness of the work and the beauty of the insect itself suggest its being in dainty hands; besides, what a thing of beauty a collection of these varicolored insects would be! It ought particularly to appeal to our young ladies of wealth, as its performance would take both time and money. No particular training or specializing in any branch of science would be required; all that would be necessary would be infinite patience, a little common sense, and the natural ability of being able to SEE, when one looks.
In order to assist some fellow-worker in these studies, the author presents these data, carried on almost up to the time of closing this manuscript, for he feels they would materially assist such a worker. The investigator will find herself placed on her mettle; and if with initiative and concentration she succeed in verifying by experiment one little thought of her own creation, she will enjoy satisfaction incomparable.
We have seen how the most dismal, long, hard, expensive experimentation was necessary to bring the wild and timid bat from its home in the mountain wilderness, without in the least subduing it from its state of Nature, to a home in civilization. So we may expect to encounter difficulties in the breeding of this beautiful and most valuable insect near our homes, in public parks, open places, or, better still, on our own lawns. Then they will clean up our diurnal mosquitoes, thereby providing for a twenty-four-hour-a-day warfare waged against that most malevolent of insects, the mosquito; by the bat at night, by the dragon fly during the day.
This is the goal that the student must set for herself. How can it be won?
CHARACTERISTICS OF THE DRAGON FLY
Dragon flies are known in various localities by different names; "snake feeders," "snake doctors," "Devil's darning needles," "mosquito hawks," and various other appellations indicating that something of superstition surrounds their existence. The study of the different species of these insects and their habits is indeed most interesting. There are many hundreds of kinds, found all over the world; and, geologically speaking, they are of most ancient origin. Fossil specimens of enormous size have been found in the lithographic limestone at Solenhofen, Germany, in deposits of Jurassic age. Some of the specimens are more than eight inches in width. When we consider the size of the present-day mosquito which serves the present-day dragon fly as food, we can draw a vivid mental picture of the size of the mosquito that served as food for the monster dragon fly of that period, nine million years ago.
To observe this creature emerging from the larva into adult life is indeed a marvelous sight. From the sluggish, ugly chitinous box, our eyes behold the development of a strong, daring, and combative creature, which in a few minutes of oxidation acquires beautiful and varied colors, and is ready to justify its existence. Darwin has termed it "The tyrant of the insect world."
The student of these creatures will not be long in concluding that they are ''One of man's best friends in the insect world," though in their own world they are indeed tyrants. Some years ago, and again only very recently, the author in studying them observed a dragon fly capture and completely devour the thorax and abdomen of a large wasp. What dexterity and valor it must display to conquer such an insect armed with such a formidable lancet fully competent to penetrate any portion of its delicate body! In the many years the author has been observing these beautiful creatures he has never seen a bird capture a single specimen; perhaps the birds indigenous to the San Antonio climate do not eat them.
ENEMIES OF THE DRAGON FLY
Spiders that weave wide and vertical webs along river banks capture quite a number of them, and then they become perfectly helpless on account of their hooked legs and large, webbed wings.
Every experienced fisherman has witnessed a trout leaping out of the water to capture a dragon fly as it glided gracefully over the surface of the water. But the escaped insect will take no more chances in flying over that particular pond or body of water, because when thus struck at, it will ascend vertically in the air like a wild duck that has been shot at, and will continue its hunt for food at some other pond or water hole.
Perhaps the beautiful and variegated color of this creature is a Nature's scheme that they may serve as food for large frogs, for bull-frogs can be seen to leap after and capture these flies on the wing. A small frog, waiting motionless for hours on some tiny eminence in an open place on the edge of a pond or pool, may appear to be just resting, or taking a sun bath; but, if we exhibit the same patience in watching him, we shall ascertain his real object. The smaller varieties of dragon flies (agrionidae) also seek some little eminence for observation, and this the tiny frogs seem to know, and they counterfeit the ground to such perfection that the dragon fly will alight on the frog's nose, when it is immediately snapped up and swallowed.
FEEDING HABITS OF THE DRAGON FLY
The large species (libellulidae) will usually select the tip of some dry exposed limb extending over the water or very near it, and adopt it as an observation point. It is interesting to watch them turn their heads, which are nearly all eyes, at each passing object, darting after it and returning to its post smacking its lips as it were, but again turning its head almost completely around at some passing flying thing. Ifwe throw a small stone within a few feet of it, it will turn its head almost completely around, as if to focus all of its many lenses on one concentration point. The largest varieties, if captured by hand, will bite hard enough to be distinctly felt.
The author and some of his friends have often witnessed the value of these insects as destroyers of mosquitoes at Mitchell's Lake. On one edge thereof bull-rushes grow luxuriantly; and toward evening dragon flies have been observed to come there and hover over these aquatic plants, darting after and capturing the emerging mosquitoes and describing one continuous ellipse, until darkness compelled them to go to roost.
The appetite of the dragon fly for the common house-fly is apparently insatiable. At a beautiful pool fed by a clear stream, near the headwaters of the San Antonio River, two of these lordly beauties flew around and around, darting here and there, then disappearing for a time, only to return shortly and resume their former dartings. The author stationed himself near their accustomed paths, caught a common house-fly, and tied to one of its legs a very thin bright-red silk thread, then allowed it to fly away. Being burdened with the weight of the silk thread, it flew slowly away, and had gone only a few feet, when one of the dragon flies turned like a flash, caught it, and, perching on a nearby limb, proceeded to devour it, which it did in an incredibly short time, the dropping of the red silk thread indicating the disappearing of the victim. This experiment was repeated so often that the author, tired of catching flies, left the place, feeling that these useful and beautiful creatures should be given a name more commensurate with the good done by them.
BREEDING OF THE DRAGON FLY
Both the dragon fly and the mosquito breed in water; and the dragon fly usually remains close to the place where it was hatched, as it is there that it finds its food. It does wander from one pool to another, as can be observed from the fact that at certain hours of the day a pool may be entirely free of dragon flies, and again hundreds can be seen hovering over the same pool a little later on. The small varieties (agrionidae) seldom venture far from their breeding places. The large varieties (libellulidae) have been observed by the author, gliding over dusty country roads, in the pursuit of their food as much as four or five miles from the nearest water, and even roosting or resting on the ground. This would indicate that small insects, other than aquatic ones, constitute some of their prey, or, perhaps, the aquatic insects becoming scarce at their accustomed places, they wander away from such localities to hunt for food.
BREEDING GROUNDS AND FEEDING GROUNDS
The source of one of the most beautiful rivers in Texas is a large lake, which, on being dammed for the water-power it affords, left a large slough where the depth of the water ranges from a few inches to several feet. The slough is out of the deep, swift current in the lake, and affords ideal conditions for the propagation of floating water-plants; and these, with the algae, formed excellent breeding grounds for mosquitoes. During the day hardly a single dragon fly can be seen, but toward evening, they visit the slough in countless thousands, flying backwards and forwards over the plant-covered surface of the water, and catching the mosquitoes, which were then beginning their nocturnal flight, until darkness precluded further observation.
In the photograph marked "Mosquito Breeding Hole" is shown an ideal mosquito-propagating place, as the water it contains is entirely seepage sewer-water. During the years 1908-9-10-11-12-13 and 14, millions of the lordly dragon flies could be seen perched on the telephone wires that parallel the county road. The limbs of the dead trees in the water were literally covered by them, as well as the barbed-wire of thesome eggs, but was more often disappointed than successful in so doing.
As the eggs are more often laid in the middle of the pond, where they cannot be reached from the shore, the author procured a hemispherical basket made of fine wire mesh, something on the order of a canary-bird's artificial nest. To it was attached a hollow tin handle, permitting the insertion of the slender end of a fishing pole. The exact spot where the fly was seen dipping was marked, or better said, not lost sight of, and as soon as possible was scooped with this device, and the contents of the scoop were searched for the eggs. The investigator will make many such scoops without finding an egg, as the fly does not drop one every time she dips her abdomen in water.
After each scoop is made, the resultant contents of the basket must be placed in a vessel containing clear water to facilitate the search for the eggs, which are quite small. However disappointment will only sharpen determination; and with patience we eventually succeed. On several occasions, the author managed to obtain eggs that hatched, after being taken from abdomens of the living flies. They evidently were fully matured, and soon would have been laid.
In the experimental tub already mentioned, where the eggs of the dragon flies were placed, a fine-meshed bobbinet was fastened several inches above the rim, as the standing water with its abundance of aquatic-plant life made it also an ideal mosquito-breeding ground. The water was thus kept mosquito-free for some time. After several of the dragon flies had hatched and developed into adults, the bobbinet was removed, more dragon fly eggs added, and subsequent developments observed.
As was to be expected, it was not long before the surface of the water was swarming with mosquito larvae (wigglers) and adult mosquitoes, without the least interference on thepart of the dragon-fly larvae, which remained on the bottom of the tub, where the mosquito larvae resorted to in order to find food. This was verified by disturbing the surface of the water, which caused the larvae or wigglers, in response to danger, to wiggle themselves to the bottom of the water, where they mingled with the dragon-fly nymphae without being in the least molested by them. It was hardly to be expected that the dragon-fly larvae would attack the wigglers in the water, as the latter creatures constantly require oxygen and spend the greater part of their lives on the surface, while the dragon-fly larvae are constantly submerged until they are ready to develop into the adult fly.
THE CRAYFISH ENEMY
That the crayfishes of the different varieties are great enemies of the dragon-fly larvae in the water is evidenced by the manner in which that crustacean obtains its food. This cougar of the under-water creatures lies in wait in its hole by the hour for some unsuspecting aquatic contemporary to pass by, when, with remarkable dexterity, its claws are brought into play, and its victim is voraciously devoured. The author has derived a great deal of pleasure from observing these creatures in shallow ponds, where they are found in great numbers, doubtlessly on account of the absence of large fish of prey.
If the larvae of the dragon fly in Nature have other enemies in the water, the author has never been able to find one, though he does not assume to be so presumptuous as to claim there are none, or to make any positive statement to that effect. Positive results can be obtained only by long, hard work and unlimited patience, involving a great deal of time. Hard work, in delving into the habits of any of Nature's creatures, has never been anything but a pleasure to the author; and, if patience had to be associated with or become a necessity in that endeavor, it was never wanting. It is certain, however, that there were no enemies in the tub; and the intention in placing mud from the bottom of the pool in the experimental vessel, was with a view of making their presence feasible or even convenient. It is quite possible that the imitated natural conditions were of a degree of perfection sufficient at least to have revealed some enemy, had it been there.
The aquatic plant commonly known as water-wort seemed to be the favorite rendezvous for both the larvae of the dragon fly and the larvae of the mosquito, on account of its delicate leaves being provided with vacuum cups forming receptacles that retain the organic matter in the water, which matter furnishes food for innumerable forms of low animal aquatic life.
It must be mentioned that the author's residence where these observations were made is within a stone's throw of the geographic centre of the City of San Antonio, and that the mosquitoes in all of these experiments were invariably of the diurnal variety. In not a single instance were the malarial-mosquito eggs or their larvae or puppae, found in the tub, confirming the knowledge that the malarial mosquito is distinctly a rural insect. Since natural conditions had been provided for them, the dragon flies developed in the tub, just as they would have developed in Nature, and so did the mosquitoesbut what was the result of the experiment?
The dragon flies captured and ate hundreds of the mosquitoes almost as fast as they developed; but here again we see a wonderful provision carried out by Old Dame Nature in the Conservation of her different species of life, in that while a batch of mosquito eggs hatch out into wigglers practically simultaneously, they do not ALL become adults at one time. Nature knows better than to place all of her eggs in one basket, so she causes only a few at a time to become adults, knowing full well the numerous vicissitudes and the many enemies they must encounter. But the few remaining dragon flies in the vicinity of the tub held the great army of mosquitoes in check, for the author and his neighbors were not particularly bothered by them.
To continue the experiment, the tub was emptied, and the conditions were reversed, that is the tub was not refilled with water until the dragon flies had all lefteven after occasional visitors had concluded that places other than the author's back yard were better for them, so ceased their visits entirely. Two weeks after refilling the tub, the author in self-defense, and out of consideration for his neighbors, was compelled to empty it, the experiment having concluded itself. The mosquitoes, not being in the least molested by one of their most formidable enemies, simply swarmed about the neighborhood. There was no room for doubt as to the cause of the difference in the two experiments, but the practical application with its merits, and with the exclusion of its demerits, is the big problem that will confront the investigator. How can dragon flies be cultivated in any receptacle without breeding swarms of mosquitoes?
ANCIENT INFORMATION CONCERNING THE
DRAGON FLY'S VALUE
It is, indeed, strange how we sometimes find information, empirically gained, hidden in some remote part of the world, which, when brought to civilization, is of untold importance to humanity. As an example of such information, long recognized but long delayed in leaving its source of origin, may be mentioned the knowledge of the value of these beautiful creatures, the dragon flies, realized for centuries by the lowly peasants or peons in some of the innermost recesses of the State of Cordova in Mexico.
The narrative that follows had its origin in the coffee-growing districts of that State, where yellow fever is practically endemic. The natives, mostly of Indian origin, knew that mosquitoes convey yellow fever, and that dragon flies prey on mosquitoes and would annihilate the said fever, if they but come in sufficient quantities. This was ascertained by simple deduction and practical observation, and was handed down to them by their ancestors. An old and highly respected citizen of San Antonio states that, in his young manhood, he was engaged in the business of coffee-buying in Mexico, that his itinerary embraced the innermost parts of that State, and that he travelled in all manners and fashions.
One day, on arriving about noon at a small hamlet, he put up his team, and after a short lunch and the conventional cup of coffee, like the natives, he resorted to a siesta. There was no difficulty in obtaining perfect quiet to insure the accustomed nap, as during these hours silence reigns supreme, when everybody is enjoying his siesta. These are no hours for business. He had hardly slept more than a quarter of an hour, when he was awakened by a perfect bedlam of all kinds of noises; shouts, yells, cries, vivas, blowing of horns, ringing of bells, beating of drums and cymbals, hoes detached from their handles and suspended with a string, pinch bars balanced and made to serve as triangles; in fact, everything with which a noise could be made was resorted to by the natives, who formed a procession marching in great glee up and down the only street in the hamlet. On coming out of his room to ascertain the cause of the row, he heard the cries of "Ya vino el mosco, ya vino el mosco! Se acaba la fiebrel se acaba la fiebre"; which translated, means "the fly has come; the fly has come! The fever will stop, the fever will stop!"
"With the greatest interest he watched the happy dancing natives in their child-like exhibitions of glee, and understanding the Spanish language, he wondered what connection the word "mosco," which means a large fly, could have in converting a sleepy old hamlet into a bedlam of noises, associated with so much joy. But as all the noisy merry-makers had uplifted faces, one glance at the skies, told him that the "moscos" were dragon flies which had descended on the hamlet in huge swarms, literally filling the air. A short walk brought him to the place of the general storekeeper (from whom he bought coffee), who, with some of the plantation owners, was contentedly watching one of Nature's marvelous displays that represented great commercial value to them. These men of the higher and educated classes, explained to our coffee-buyer, that, when the dragon flies came in such numbers, the yellow fever, which interfered so much with the labor employed in their enterprises, would be entirely routed, as the flies came to prey on the mosquitoes that convey the fever, and in a short time, would completely exterminate them. They further told him that all of the natives knew the value of dragon flies, and early taught their children never to kill a single one, the information having been handed down for centuries from generation to generation.
This huge migration on the part of these valuable creatures occurred in the fall of each year. Thus we see that information of incalculable value was indeed ancient knowledge centuries before our noble American scientists made their wonderful discovery in Cuba.
As the food of dragon flies is principally mosquitoes and other small insects, the student will find great interest and good entertainment in the study of the scatology of these creatures, the necessary accoutrement being a lower-power microscope, such as can be bought from any optical-goods dealer, a few concave watch glasses, and a vial of peroxide of hydrogen. To obtain the best results, the large dragon flies ought to be captured as late of an evening as possible. They are then placed under a convenient glass globe over the bottom of which is spread white paper. The next morning on the paper will be found several small pieces or pellets of excrement. These are then placed on the watch glass, and a few drops of the peroxide are poured on them. An effervescence will be observed; and after that subsides, the little masses will have fallen apart, the peroxide having dissolved the mucous that binds the individual pieces together.
If we then place the watch glass under the microscope, we shall find the skeletal remains of the insects the fly has devoured; because, as already mentioned in the study of the scatology of bats, the external body of all insects is of that character of tissue known as chitin, which is perfectly insoluble, and hence passes through the digestive system of the dragon fly intact, except that it is found comminuted by the chewing or grinding apparatus of the insect. Further amusement and entertainment can be had, if we will catch a number of mosquitoes, and, after they are perfectly dried, in imitation of the grinding apparatus of the dragon fly we will chop them up very fine with an old safety razor, we shall obtain the identical conditions of the pellets or excrement. When we place them in a watch glass and add a few drops of peroxide of hydrogen, we shall get the same picture.
The peroxide dissolves out the albuminous matter, leaving the chitin untouched, on account of its insolubility. In this manner we become familiar with the comminuted chitinous remains of mosquitoes from the bodies of dragon flies. More interest can be added to the study, if we make hand-drawings of the individual pieces we see under the microscope ; and we shall become so familiar with the comminuted pieces of mosquitoes, that we shall immediately recognize and distinguish them from the comminuted remains of other insects in the pellets we examine.
THE TOP-WATER MINNOW
The top-water minnow, which has received many well-deserved encomiums as a destroyer of mosquitoes, is also a great enemy of the dragon fly. The success in combating mosquitoes with this little fish and its different species in large bodies of water depends on the presence or absence of larger fish. With this feature of such warfare the author has had considerable experience, for he possesses a large reservoir of flowing water where he raises fish for study, pleasure, and food. As the whole of life is a question of food, conditions for food for the food-fish were well considered.
AUTHOR'S FISH CULTURE
When this body of water was adopted for fish culture, there were profusely provided aquatic mosses and plants. When these had attained sufficient growth, top-water minnows by the thousands were placed in the water, not for their mosquito-destroying value, but for their value as food for other fish. The planting of the aquatic plants in the edge of the water was for the special protection of the minnows. By continuous feeding of ground meat and table scraps, they multiplied in great numbers.
To the reservoir were then added the different species of perch by the hundreds, and lastly, the different species of trout or bass intended for culture, and found in this vicinity. The venture is a success, as the bass feed on the perch, and the perch in turn feed on the minnows that are practically hand-fed. These little fishes increase rapidly because of the fact that they do not spawn like their higher or larger brothers, so have no eggs to pass through the different vicissitudes, or to fill the yawning maws of aquatic enemiesthey bring forth their young alive. Notwithstanding this feature, plus the splendid protection the aquatic plants afford them, and the abundance of food they receive, the author is compelled every now and then to replenish his stock of minnows to feed the perch, which in turn feed the bass.
SUGGESTED BREEDING GROUND FOR DRAGON FLIES
As most farms are compelled to have earthern tanks to impound water for their stock, and as such places are excellent breeding grounds for mosquitoes, and as none of the usual mosquito-destroying methods can be applied to them, the author offers a plan, which the schematic drawing illustrates. One end of the tank is fenced with barbed wire, and on the inside of the enclosure, ordinary wire is stretched from bank to bank, and reaching to the bottom of the water. The barbed-wire fence is to keep out stock, and the wire netting to keep out the enemies of the dragon flies and their eggs, which are top-water minnows, crayfish, and the different species of perch, which are the enemies of the species of dragon flies that go under the water to lay their eggs.
This scheme also conserves the different species of the smaller dragon flies, the agrionidaethe species shown in the cut as having the slender abdomens. These species seldom wander any distance from the water, and usually rest on floating weed or water-moss, dipping their long and delicate abdomens in the water while in the act of ovipositing. It is then that the small perch nips off the slender abdomen, which, of course, kills the insect. As the suggested fencing is inexpensive, it is hoped many such places will be made for the conservation of one of Nature's creatures whom we know to be an enemy of the arch fiend of the insect world.
EXPERIMENTS ON OILING OF WATER
Under the dense shade of a large pecan tree, in the author's back yard, a wooden tub was filled with cistern water for the purpose of breeding mosquitoes, and of observing the effects of the oiling method in their destruction. Almost the next day eggs were found on the surface of the water, which duly hatched out into the larvae or wigglers. When these were about half grown, the surface of the water was given a liberal coat of kerosene oil, as that oil spreads much better than does any other. Of course, all of the wigglers in the tub, including the new arrivals were drowned, but on the morning of the 7th or 8th day after the oiling, the surface of the water was again well dotted with mosquito eggs laid in between the islands of the gummy residuum left by the evaporating oil. When these hatched out, the wigglers, coming to the surface of the water for air, on encountering a lump of the residuum, would wiggle about until they found an open breathing space between the islands.
There is nothing original or singular about this procedure, except that, in the course of time, the water, on account of the many layers of oil being churned into it by the frequent additions of fresh water poured into the tub to make up for evaporation, became so impregnated with the oil, that none of the ordinary minute aquatic plants that usually find their way into bodies of standing water developed in the tub. The domestic animals about the yard refused it as drinking water, yet, notwithstanding all this, the mosquitoes continued to lay their eggs on the water in the tub as though it were perfectly fresh, and these eggs hatched out into larvae and pupae, until they were killed off by a new layer of oil.
In the outskirts of the City of San Antonio a pool of standing water was formed in the bed of a dry creek, some three hundred yards below a large artificial lake. The pool was about 18 feet long, six or eight feet wide, and from nothing to fifteen inches in depth. This depth was fairly constant, as it was formed by seepage from the big lake, though during very dry times the level of the water in there would fall so low as to cause the pool to go dry.
It was to this pool that the author so often resorted in the study of dragon flies, on account of the natural conditions there prevailing. The total absence of the top-water minnow, on account of the pool at times becoming dry, the slimy ooze, the aquatic moss and other numerous kinds of water plants, the huge complement of miscroscopic aquatic fauna, and, to make conditions more ideal, the dense overhanging brush on one of its banks afforded the requisite shade. This was the place selected for the study and observation which so forcibly reveal the fallacy in the oiling method mentioned in the concluding paragraphs of ALLEGATION THREE, and which will impress with its demerits the sanitarian employing this method of mosquito eradication.
The author spent hours and hours at this natural mosquito-and-dragon-fly breeding place, observing the latter creatures in their antics, dartings, quarrels, love-making, and continually dipping of their abdomens in the water in the act of ovipositing, and, in particular, the beautiful different iridescent colors of these miniature natural aeroplanes. Nothing that moved in their world seemed to escape their large limpid eyes.
This pool seemed to be quite a resort for these creatures, as frequent visitors made their appearance, darting here and there, but remaining for a short time only. There seemed also to be among them some toughs and bullies, as the permanent residents yielded their favorite places for observation to the visitors, without the least protest, resuming their points of vantage only after the usurpers had left.
Dragon flies could be seen in numbers disporting over the surface and on the shore of the large lake, and also perched on convenient places over a small pool immediately below the dam. This small pool was teeming with top-water minnows.
A little before sunset it seemed as though all of the dragon flies from the lake and elsewhere came to our pool; the air was full of them. This is readily accounted for, because the mosquitoes that bred in this pool in countless numbers were principally of the nocturnal varieties, as there were hardly any seen during the day. Those that hatched out during the day were devoured by the dragon flies, and those that escaped, of course knowing of the immediate presence of their enemies, hid away until evening in the dense brush that afforded the pool the requisite shade.
When the student attempts to capture one of these creatures with an ordinary insect net, he will become acquainted with their remarkable vision and their rapidity of flight, as he will make many dashes with his net, only to find the dragon fly just a little ahead of it. He will soon learn that, to capture one, it will be necessary for him to swing his net as hard as he would swing a baseball bat to swat a ball when all the bases are full.
As the pool was some three miles from the author's home, and as most of these observations were made before the universal use of that wonderful invention, the automobile, that distance had to be covered with a horse and buggy and was of some moment, as it meant considerable loss of time to travel six miles there and back to the "mill," the author's private office, from where he, the "miller", obtained the necessary means for the sustenance of his little family and for the prosecution of his experiments. Therefore he again resorted to his old wooden tub, and converted it into use for a check, or parallel observation, on the mosquitoes in the pool, since the behaviour of those in the tub would be the same as that of those in the pool three miles away.
Accordingly, he refilled the wooden tub in his back yard with rain water, and, to imitate conditions in the pool, added a lot of mud and decaying leaves. The next day many mosquito eggs dotted the surface of the water; and, when these hatched out, the water in the pool was covered with kerosene oil, as was the water in the tub. Of course, the mosquitos in both the tub and the pool were killed.
After a wait of eight days, the water in the tub was again well dotted with mosquito eggs, and an observation of the water in the pool showed the same. After the lapse of a few days more, both tub and pool were again oiled, and again the mosquito larvae were killed. Convinced that the parallel tub had well served its purpose, it was emptied and turned upside down. After a lapse of ten or twelve days from the second oiling, the pool was again oiled, but this time with most painstaking care to cover the smallest surface of the water; in fact, oil was used in profusion, as this was the last oiling it was to receive.
In the immediate vicinity of this pool were several very poor Mexican squatters who had erected their humble little huts out of scrap tin and scrap lumber, binding the side walls with mud, and living practically under the brush arbors erected in front of the dwellings.
With the very first oiling the dragon flies left; hardly a single specimen was to be seen, where previously countless hundreds or even thousands found a happy home. Three weeks after the oiling was stopped, mosquitoes swarmed there in such numbers that the poor Mexican squatters, who had so laboriously built their huts, were compelled to tear them down and move away. The Mexicans of this class are the most humble and uncomplaining people imaginable; and when the mosquitoes got too bad for them, they must have been indeed intolerable. They related to the author, that, before the oiling, they were not in the least molested by mosquitoes during the day, but after the last oiling, they could not even enjoy their siesta in the afternoon; and at night their huts became a swarming mass of mosquitoes whose onslaughts were simply unendurable, hence they were compelled to move from that locality.
From this we see that, while the first and the second oilings most effectively destroyed the mosquitoes developing in the pool, it also most effectively destroyed the larvae of the dragon flies which were constantly developing in the same water, as, in emerging into adult life, they were compelled to pass through the layer of oil to reach the surface and out of the water entirely to emerge from their chitinous shell. In fact, the second and the third oilings were spaced with the view of destroying the larvae of the dragon flies, as in quite a number of instances these take some time to develop.
As already stated, a very short time after the first oiling the dragon flies left this pool, and so complete was this migration that the next day, after hours of patient observation, hardly a single fly was seen; and towards evening, when they used to come by the thousands, not a single one put in its appearance. They had migrated to some other pool or pond, where the natural conditions had not been disturbed, and where they could continue to live their lives as their Creator intended they should. But to the mosquitoes, with their prolificacy, this disturbance of Nature was only temporary and greatly to their advantage, as it rid them of an active enemy, leaving them the pool all to themselves.
The experiment thus carried out clearly proves the fallacy in the oiling method of mosquito eradication, and demonstrates how Nature resents any interference in her wonderful balancing. It also indicates the constancy and fidelity which must attend the method to overcome its fallacy, for otherwise, it will result in defeating the very object we desire to attain, viz, the eradication of mosquitoes.
SUGGESTED CONTINUATION OF EXPERIMENTS
As there is so much to be learned about these valued friends of man in the insect world, the author will continue their study at every opportunity that presents itself, as it involves the learning of the habits of a diurnal enemy of the mosquito, which enemy we are indeed fortunate in possessing. It was suggested in the beginning of this writing that some young and enthusiastic student take up these studies; and, if such a person enter this field and think the author can be of the slightest assistance to him or her, that person can rest assured that whatever information the author has will be cheerfully given. If the problem pointed out, viz, the cultivation of dragon flies in a receptacle at hand wherever wanted, with the exclusion of breeding mosquitoes, can be solved, it will not only bring name and fame to crown his or her efforts; but deep down in the innermost recesses of the heart will firmly be imbedded the proud satisfaction of doing the noblest of all things, helping one's fellow man.
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