CHAPTER IV
Ridding Stagnant Water of Mosquitoes
Because of the serious and often fatal injury it inflicts on man, the most dangerous animal known is the mosquito. Compared with the evil done by the insect pest, the cobra's death toll is small. This venomous serpent is found only in hot countries, particularly in India, while mosquitoes know no favorite land or clime—unless it be Jersey. Arctic explorers complain of them. In Alaska, it is recorded by a scientist that "mosquitoes existed in countless millions, driving us to the verge of suicide or insanity." A traveler on the north shore of Lake Superior, when the snow was several feet deep, and the ice on the lake five feet in thickness, relates that "mosquitoes appeared in swarms, literally blackening the banks of snow in sheltered places."
Mosquitoes Responsible for Yellow Fever
In the temperate zone this evil-breeding insect was, until recent years, considered more in the light of an exasperating pest. It is now known, however, that malaria is due entirely to the bites of mosquitoes. But it is in the tropical countries that their deadliest work is done. There, it has been proved beyond question, the mosquitoes are responsible for the carriage of yellow fever. If, in a yellow-fever ridden region, one were to live entirely in an inclosure, carefully protected with proper screens—as certain entomologists did—there practically would be no danger from the dread disease, even if all other precautions were neglected.
Effect of a Mosquito Bite
The crime committed by the mosquito against its innocent victim, man, is more in the nature of manslaughter than of murder, according to the authorities. There is no premeditated malice. "A mosquito bites primarily to obtain food," says a leading entomologist; "there is neither malice nor venom in the intent, whatever there may be in the act." There isn't great comfort in the intelligence conveyed by the scientist, nor in his further observation:
"Theoretically, there would seem to be no reason why there should be any pain from the introduction of the minute lancets of the insects, and the small amount of bloodletting is usually a benefit rather than otherwise. Unfortunately, however, in its normal condition the human blood is too much inclined to clot to be taken unchanged into the mosquito stomach; hence, when the insect bites, a minute droplet of poison is introduced, whose function it is to thin out the fluid and make it more suitable for mosquito digestion. It is this poison that sets up the inflammation and produces the irritation or swelling.... The pain is caused entirely by the action of the poison in breaking up the blood, and, as the first act of a biting mosquito is to introduce the poison into the wound, the pain and inflammation will be the same, whether the insect gets its meal or not. In fact, it has been said that if a mosquito be allowed to suck its fill and then fly, the bite will not itch, and there is just a basis of justification for this."
To make a scientific inquiry into the habits of the mosquito, and to do it patiently, one should be far from the maddening swarms, or at least effectively screened in. Then it would be possible to believe the statement of the Government's entomologist that not "one mosquito in a million" ever gets the opportunity to taste the blood of a warm-blooded animal. As proof of this there are, in this country, great tracts of marshy land never frequented by warm-blooded animals, and in which mosquitoes are breeding in countless numbers. The point is emphasized by the prevalence of mosquitoes in the arctic circle and other uninhabited regions.
If this gory insect does not live by blood alone, how is it nourished? Female mosquitoes are by nature vegetarians; they are plant feeders. Why they should draw blood at all is a question which remains unsolved by entomologists—as well as by the suffering victims. The females have been observed sucking the nectar from flowers; obtaining nutriment from boiled potatoes, even from watermelon rinds, from which they extract the juice. As regards the blood habit, the male mosquito is a "teetotaler." Just how this male insect lives, scientists have not determined. He may not take nourishment at all. At any rate, the mouth parts of the male are so different from those of the female that it is probable his food is obtained differently. The male is often seen sipping at drops of water, and a taste for molasses is ascribed to the male mosquito by one authority.
Presence of Mosquitoes Depends Upon Winds
A common remark heard along the Jersey shore, also on Long Island, is this: "When we have a sea breeze we are not troubled with mosquitoes, but when there comes a land breeze they are a pest." While this observation is true, the reasons therefore entertained by the unscientific mind are erroneous. The matter of the absence or abundance of mosquitoes in varying winds is closely related to the inquiry which entomologists have made: how far will mosquitoes fly? Says one investigator:
"The migration of mosquitoes has been the source of much misapprehension on the part of the public. The idea prevalent at our seaside resorts that a land breeze brings swarms of mosquitoes from far inland is based on the supposition that these insects are capable of long-sustained flight, and a certain amount of battling against the wind. This is an error. Mosquitoes are frail of wing; a light puff of breath will illustrate this by hurling the helpless creature away, and it will not venture on the wing again for some time after finding a safe harbor. The prevalence of mosquitoes during a land breeze is easily explained. It is usually only during the lulls in the wind that Culex can fly. Generally on our coast a sea breeze means a stiff breeze, and during these mosquitoes will be found hovering on the leeward side of houses, sand dunes, and thick foliage.... While the strong breezes last, they will stick closely to these friendly shelters, though a cluster of houses may be but a few rods off, filled with unsuspecting mortals who imagine their tormentors are far inland over the salt meadows. But if the wind dies down, as it usually does when veering, out come swarms upon swarms of females intent upon satisfying their depraved taste for blood. This explains why they appear on the field of action almost immediately after the cessation of the strong breeze; on the supposition that they were blown inland, this sudden reappearance would be unaccountable."
A sultry, rainy period of midsummer is commonly referred to as "good mosquito weather." The accepted idea is that mosquitoes are much more abundant at such times. This is true, and the explanation is simple. Mosquito larvæ, or wrigglers, as they are termed, require water for their development. A heavy shower leaves standing water, which, when the air is full of moisture, evaporates slowly. Then, too, the heat favors the growth of the microörganisms on which the larvæ feed; wrigglers found in the water forty-eight hours after their formation will have plenty of food, and adult mosquitoes will appear six to eight days after the eggs are laid. Clear weather, with quick evaporation, interferes with the development of the wrigglers, so that a season with plenty of rain, but with sunshiny, drying weather intervening, is not "good mosquito weather."
Destroy the Larvæ
Inasmuch as a generation of mosquitoes appear to torment man within ten days, at the longest, after the eggs are laid; as a batch laid by a female mosquito contains from two hundred to four hundred eggs; as from each egg may issue a larva or wriggler which in six days will be an adult mosquito on the wing—it is to the destruction of the larvæ that attention should be directed. The larva is a slender organism, white or gray in color, comprising eight segments. The last of these parts is in the form of a tube, through which the wriggler breathes. Although its habitat is the water, it must come to the surface to breathe, therefore its natural position is head down and tail, or respiratory tube, up. Now, if oil is spread on the surface of a pool inhabited by mosquito larvæ, the wrigglers are denied access to the air which they must have. Therefore, they drown, just as any other air-breathing animal would drown under similar circumstances.
Best Preventive Measures
As to the best methods to employ in ridding a country place, or any other region, of mosquitoes, the directions furnished by Dr. L. O. Howard, the Government entomologist, who has been a careful student of the problem since 1867, are of great value:
"Altogether,[3] the most satisfactory ways of fighting mosquitoes are those which result in the destruction of the larvæ or the abolition of their breeding places. In not every locality are these measures feasible, but in many places there is absolutely no necessity for the mosquito annoyance. The three main preventive measures are the draining of breeding places, the introduction of small fish into fishless breeding places, and the treatment of such pools with kerosene. These are three alternatives, any one of which will be efficacious and any one of which may be used where there are reasons against the trial of the others."
Quantity of Kerosene to be Used
"The quantity of kerosene to be practically used, as shown by the writer's experiments, is approximately one ounce to fifteen square feet of water surface, and ordinarily the application need not be renewed for one month.... The writer is now advising the use of the grade known as lubricating oil, as the result of the extensive experiments made on Staten Island. It is much more persistent than the ordinary illuminating oils.... On ponds of any size the quickest and most perfect method of forming a film of kerosene will be to spray the oil over the surface of the water.... It is not, however, the great sea marshes along the coast, where mosquitoes breed in countless numbers, which we can expect to treat by this method, but the inland places, where the mosquito supply is derived from comparatively small swamps and circumscribed pools. In most localities people endure the torment or direct their remedies against the adult insect only, without the slightest attempt to investigate the source of the supply, when the very first step should be the undertaking of such an investigation.
"The remedy which depends upon draining breeding places needs no extended discussion. Naturally the draining off of the water of pools will prevent mosquitoes from breeding there, and the possibility of such draining and the means by which it may be done will vary with each individual case. The writer is informed that an elaborate bit of work which has been done at Virginia Beach bears on this method. Behind the hotels at this place, the hotels themselves fronting upon the beach, was a large fresh-water lake, which, with its adjoining swamps, was a source of mosquito supply, and it was further feared that it made the neighborhood malarious. Two canals were cut from the lake to the ocean, and by means of machinery the water of the lake was changed from a body of fresh to a body of salt water. Water that is somewhat brackish will support mosquitoes, but water that is purely salt will destroy them."
Employing Fish to Destroy Larvæ
"The introduction of fish into fishless breeding places is another matter. It may be undesirable to treat certain breeding places with kerosene, as, for instance, water which is intended for drinking, although this has been done without harm in tanks where, as is customary, the drinking supply is drawn from the bottom of the tank. The value of most small fishes for the purpose of destroying mosquito larvæ was well indicated by an experience described to us by Mr. C. H. Russell, of Bridgeport, Conn. In this case a very high tide broke away a dike and flooded the salt meadows of Stratford, a small town a few miles from Bridgeport. The receding tide left two small lakes, nearly side by side and of the same size. In one lake the tide left a dozen or more small fishes, while the other was fishless. An examination by Mr. Russell in the summer of 1891 showed that while the fishless lake contained tens of thousands of mosquito larvæ, that containing the fish had no larvæ. The use of carp for this purpose has been demonstrated, but most small fish will answer as well. The writer knows of none that will be better than either of the common little sticklebacks (Gasterosteus aculeatus or Pygosteus pungitius)."
Is mosquito fighting a success? This question is an all-important one, not only to the summer resident, but also to cities and towns contiguous to salt-water marshes, or to swampy lands, well suited for mosquito breeding. The answer is this: Mosquito control is possible; actual extermination impossible with an insect that develops so rapidly. The "Jersey mosquito," the unscientific name popularly given to an insect of huge size and ravenous appetite, has become famous. As a matter of fact, the species of mosquitoes found in New Jersey are no more rare or varied than those found on Staten Island or on Long Island. But until very recently the region lying between Jersey City and Newark has been particularly favorable to the development of mosquito larvæ. It has been announced in the press that mosquitoes have been driven out of the Newark meadows. This is an exaggeration, of course, but the work accomplished there is remarkable, and other infected regions may take heart from the marked success which has attended the efforts of Dr. John B. Smith, Entomologist of the New Jersey State Agricultural Experiment Station.
Remarkable Work Accomplished
The salt marsh lying within the limits of the city of Newark covers an area of about 3,500 acres. It extends from a point on the Passaic River to the mouth of Bound Creek, where it empties into Newark Bay. Its length is about eight miles and it has an extreme width of three miles. The Newark marsh problem was a very complex one. The meadows are cut into many sections by the several traversing railroads and by creeks; this materially influences the drainage. The Peddie Street sewer crosses the marsh in a straight line of about three miles from the city to the bay. This sewer is twenty feet wide, and its banks are from three to four feet above the marsh land.
An experiment with machine ditching was made in 1903. The worst parts of the marsh were selected, and about 40,000 feet of ditches were cut. These ditches were six inches wide, two feet deep, and the drainage was perfect from the outset. The section of meadow thus drained became so dry in consequence that the grass growing there can now be cut by a machine in summer, whereas formerly the hay could be mown only in winter. The work was so successful that the Newark Common Council appropriated $5,000 to complete the mosquito drainage of the marsh. Of the results obtained up to this spring, Dr. Smith says:
"This Newark marsh problem was an unusual one, and one that would not be likely to recur in the same way at any other point along the coast. Nevertheless, of the entire 3,500 acres of marsh, not 100 acres remain on which there is any breeding whatever, and that is dangerous only in a few places and under certain abnormal conditions. Including old ditches cleaned out, about 360,000 running feet of ditches have been dug on the Newark marshes, partly by machine and partly by hand, and if the work is not entirely successful, that is due to the defects which were not included in the drainage scheme. It is a safe prediction, I think, that Newark will have no early brood of mosquitoes in 1905, comparable with the invasions of 1903 and 1904."
This prophecy has proved true.
The Campaign on Long Island
The wealthy summer residents along the north shore of Long Island, keenly alive to the necessity of driving mosquitoes from the region where they spend so much of their time, have attacked the problem in a scientific, as well as an energetic way. The North Shore Improvement Association intrusted the work to Henry Clay Weeks, a sanitary engineer, with whom was associated, as entomologist, Prof. Charles B. Davenport, Professor of Entomology at the University of Chicago and head of the Cold Spring Biological Laboratory; also F. E. Lutz, an instructor in biology at the University of Chicago. Prof. N. S. Shaler, of Harvard University, the most eminent authority in the country on marine marshes, was retained to make a special examination of the salt marshes with a view to recommending the best means of eliminating what were the most prolific breeding grounds of mosquitoes. A detailed examination of the entire territory was made. Practically every breeding place of mosquitoes, including the smaller pools and streams, and even the various artificial receptacles of water, were located and reported on. Mr. Weeks, with his assistant, then examined each body of water in which mosquito larvæ had been found, with a view to devising the best means of preventing the further breeding of mosquitoes in these plague spots. Finally, a report was prepared, together with a map on which was located every natural breeding place.
Investigations in Connecticut
Important investigations have been made in Connecticut by the Agricultural Experiment Station, under the direction of W. E. Britton and Henry L. Viereck, and the results have been most encouraging. Dr. Howard, in his directions for fighting mosquitoes, acknowledges his indebtedness to the very successful experiments carried on at Staten Island. Maryland is aroused to the point of action. Dr. Howard A. Kelley, of Johns Hopkins University, is to coöperate with Thomas B. Symons, the State entomologist, in carrying the war to the shores of Chesapeake Bay. "Home talent," moreover, can accomplish much. To fight intelligently, let it not be forgotten that the battle should be directed against the larvæ. These wrigglers are bred for aquatic life; therefore, it is to all standing water that attention should be directed. Mosquito larvæ will not breed in large ponds, or in open, permanent pools, except at the edges, because the water is ruffled by the wind. Any pool can be rendered free from wrigglers by cleaning up the edges and stocking with fish. Every fountain or artificial water basin ought to be so stocked, if it is only with goldfish. The house owner should not overlook any pond, however small, or a puddle of water, a ditch, or any depression which retains water. A half-filled pail, a watering trough, even a tin receptacle will likely be populated with mosquito larvæ. Water barrels are favorite haunts for wrigglers.
A Simple Household Remedy
There are those, however, who will obstinately conduct their campaign against the adult mosquito. If energetic, such persons will search the house with a kerosene cup attached to a stick; when this is held under resting mosquitoes the insects fall into the cup and are destroyed. Those possessed of less energy daub their faces and hands with camphor, or with the oil of pennyroyal, and bid defiance to the pests. With others it is, Slap! slap!—with irritation mental as well as physical; for the latter, entomologists recommend household ammonia.
FOOTNOTES:
[3] See Bulletin No. 25, U. S. Department of Agriculture, Division of Entomology.