Popular Science Monthly/Volume 66/January 1905/The Mosquito Investigation in New Jersey
|THE MOSQUITO INVESTIGATION IN NEW JERSEY.|
By Professor JOHN B. SMITH, Sc.D.,
WHEN, a few years ago, it began to be generally realized that mosquitoes besides being sources of annoyance, were also dangerous to life and health because of their relation to certain diseases, the question of whether or not control or even practical extermination was feasible began to be seriously considered. Not until then was it realized how little was actually known of these pests and that, as a matter of fact, only a few species had been followed throughout their entire life cycle. It was assumed that all the species of the same genus had approximately the same life history, that the adults had practically identical habits, that what had proved successful in one locality would answer as well in all others, and that each locality with sufficient energy might secure exemption for itself.
The little book on 'Mosquitoes' by Dr. L. 0. Howard, issued in 1901, summarizing what was then known, was published at the psychological moment and exerted an enormous influence. Mosquito brigades were formed, and improvement and other societies began work enthusiastically. New Jersey has always had something of a reputation in the mosquito line and at several points active work was begun. There were not wanting those that lacked faith, however, and there was abundant ridicule for those engaged in the work which, by the way, did not turn out as well as had been expected. We had now three classes in the state—the unbelievers and scoffers who were in the vast majority; the enthusiasts who believed firmly in local work, who formed a small but powerful minority, and a yet smaller class who thought that there might be a chance to get money out of it and who urged improvements that they might be engaged to carry out.
As the entomologist of the Agricultural Experiment Station, as well as in his capacity of state entomologist, the writer followed some of this early work, rather as a sceptic than otherwise; but after a season's observation found reason to believe that while eventual success in the direction of mosquito control could probably be obtained, the factors of the problem were not understood and that much work and money was being wasted or misapplied. The danger was that if failure resulted through ignorance the entire movement might be discredited and delayed.
Presenting the matter to Dr. E. B. Voorhees, the director of the station, he was authorized to ask the state legislature for a sum of money sufficient to make such a study of the problem as might be necessary to enable him to make practical recommendations, suited to conditions as they actually existed in New Jersey. Though at first inclined to treat the matter as a huge joke, the law-making body did pass the necessary act appropriating ten thousand dollars for the purpose declared, and this amount, it was intended, should cover two years of work; the minimum of time considered necessary. As a matter of fact it was spread over three years and the investigation is now completed. The detailed report is in the hands of the governor and will be printed in due course; but it may be interesting to summarize some of the conclusions for general information.
It is positively demonstrated that of the thirty-five species of mosquitoes occurring in New Jersey only a few are ever troublesome, and that not more than half a dozen need be considered from the practical standpoint. It has been further found that in this state the mosquito is not a local problem and that in many cases the pest that makes porches uninhabitable at night was bred miles away.
Beginning at the head of Newark Bay, the coast extending southward is edged with a fringe of salt marsh, broken only for a short stretch along Baritan Bay, and from Long Branch to Point Pleasant; and even here every stream has such an edging. Beginning at Bay Head there is an outer bar or strip of sand varying in width from half a mile to two miles or more, broken at irregular intervals but reaching to Cape May. On this narrow shore strip summer resorts like Seaside Park, Barnegat City, Beach Haven, Atlantic City, Ocean City and many others have developed and there is no better beach in the world for bathing and other aquatic sports. Between this outer fringe and the mainland is an area of low marsh, broken into islands by channels, with bodies of water, some large like Barnegat Bay and Great Bay, the majority small. Broad stretches of such marsh also extend along the large rivers of South Jersey so far as the tide makes the water distinctly brackish. Along the Delaware Bay shore the mainland extends closer to the water's edge and the salt marsh areas are smaller, and they gradually disappear along the banks of the river going north, as the water becomes fresh. Altogether there are many thousands of acres of such marsh and on it, in water ranging from fresh to salt, breed four species of mosquitoes. They breed there and nowhere else in the state; but practically two of these salt marsh forms dominate the country for from twenty to forty miles back. In other words they migrate in immense swarms from the places where they were developed and live for weeks or even months in places where, but for them, mosquitoes would be unknown.
The two troublesome species are Culex sollicitans and C. cantator. A third species, C. taniorhynchus is also a migrant, but occurs in much smaller numbers and does not fly so far. The fourth, C. salinarius does not seem to migrate. Except the last, all these species lay their eggs singly in the marsh mud, not in water, and these eggs will maintain their vitality for months during the summer and remain unhatched during the winter. But when they become covered in summer by a spring tide or a heavy rain they hatch within an hour or two, and millions of wrigglers will be found on a marsh after a storm, where none were seen the day before. In a week these wrigglers are ready for the change to pupa and adult. After the adults have hatched, the first warm sultry night sends swarms numbering millions over the surrounding country. Few of these ever get back and none that leave the marsh finally ever reproduce their kind. In C. sollicitans only the females migrate and all those that were examined proved sterile; the migratory instinct replaces the desire to multiply. In C. cantator both sexes fly; but the males drop out after a few miles have been covered, and the females are sterile as a rule; a few exceptions have been found.
It might seem that having said so much, I had placed the problem of control beyond reasonable hope of practical solution; but the statements are yet incomplete and were left so to bring out forcibly the fact that it is no local matter: it is one with which the state must deal comprehensively. In truth not ten per cent, of that vast marsh area breeds mosquitoes at any time, and even a breeding area is not uniformly bad. The mosquito demands water free from fish or predatory insects of all kinds, that shall remain for at least a week. As a rule wherever tides go, the little species of Fundulus or 'killifish' will go and where they go no wrigglers can exist. Wherever fiddler crabs inhabit a marsh area, and there are thousands of acres so inhabited, their holes drain it completely and afford no chance to breed. It is usually at the edge of the highland, where the tide water works in through grass so dense that it bars fish and fills depressions, that the mosquitoes get their best chance and in a number of surveyed areas it was only the edge of the marsh that was reported dangerous. Other danger spots are the irregular, rather high marshes rarely covered by tides, which dry out completely at times, killing all aquatic life, and then fill all depressions by a heavy storm. Cat-tail marshes when they are at all dense are safe from mosquito breeding.
A very thorough survey of the entire salt marsh area determined that not over ten per cent, of it is at all dangerous, and the question arose, what can be done to make that portion safe. Of course any scheme that provided for the reclamation of the marshes and made them available for agricultural or other industrial purposes would also eliminate mosquito breeding places; but that sort of reclamation is expensive and the total bill would be so great as to make it impossible to obtain consideration from any legislature. For the purpose of preventing mosquito development, reclamation is not necessary; it needs only such works as will enable all surface water to drain off completely in less than a week, or as will fill all depressions to a general level, whatever that general level may be.
The average marsh bottom is a tough clayey mud of variable depth, overlaid by a turf from six inches to a foot or more in thickness. This material is like a huge sponge from which the water will run out if it gets a chance, and which will absorb an enormous quantity of surface water. Its texture is also such that it will maintain even a narrow ditch perfectly and, if it is deep enough—two feet or more—no growth will start from the bottom. For slow drainage a ditch six inches wide, that will affect from thirty to fifty feet on each side can be cut by machine, and will dry off even the heaviest precipitation of rain in twenty-four hours. If a spring tide soaks the marsh the drainage is slower; but the surface will be free of shallow pools within forty-eight hours.
Lest it should be considered that this is all a statement of belief merely it should be said that in 1903 several bad areas near Newark and Elizabeth were experimentally ditched. When the work was begun the marshes were soft, full of holes, water-logged and hip boots were a necessity. The crop of salt hay could not be gathered until winter and lawn shoes for horses where they could be used at all, were a necessity. Throughout 1904 it was possible to walk over the drained area at all times, dry-shod except after heavy rains, and then twelve hours were enough to dispose of every pool or puddle. The crop of hay was heavier than for many years past, much of it was cut by machine and horses could be taken everywhere. Practically no mosquitoes developed on these areas.
The most convincing work however was. done on the Shrewsbury River, extending from Seabright to North Long Branch and including nearly all the marsh area on both Monmouth Beach and Rumson neck sides of the stream. The territory had been roughly surveyed during the season of 1903 under the direction of local associations, and during the winter, at the request of these associations, one of the field agents and afterward an engineer was sent down to lay out a general drainage scheme. Before even the frost was out of the ground work was begun, and very soon afterward, in early March, wrigglers made their appearance in every pool and millions of potential mosquitoes were on the marsh. But the weather remained cold, larval growth was slow and the work was systematically pushed so as to reach the worst places first, the sods removed from the ditches being used to fill the small deep holes that would naturally drain most slowly. Toward the end of the task in April, it became a race between the ditchers and the insects, which were beginning to pupate. The ditchers won and the last pool was drained before the first adult mosquito issued. It was interesting to watch a new ditch just opened into tide water, flowing in a steady stream toward the outlet and carrying a surface cargo of wrigglers and pupæ; and yet more interesting was it to see the 'killies' at the ditch mouth, taking care of every specimen that came out and gradually running up the ditch to meet them. On these hundreds of acres of meadow not one of the
millions of mosquito larvæ came to maturity. On the marshes to the north and south where no work was done, the mosquito output was phenomenal and the early summer of 1904 will be long remembered. Not only the nearby cities and towns were sufferers, but the insects actually crossed both ridges of the Orange Mountains in their travels to the west, and swarmed in the hills about Paterson to the north. And in all this the Shrewsbury River country was practically free from mosquitoes and remained so all summer! There were some local fresh-water species that proved troublesome later in the season; but these were dealt with as fast as their breeding places were located. The marsh mosquitoes that had been the pest of previous years were conspicuous by their absence. A yet greater work was done by the City of Newark, where 3,500 acres of salt marsh were dealt with. No results were apparent in 1904, because the heavy early broods were allowed to develop unchecked; but the marsh is now dry except in a very small section, and the spring of 1905 should tell an interesting story. There will be some mosquitoes, of course, because of the Elizabeth, Kearny and Jersey City marshes that are so near by. Elizabeth is showing an intelligent interest in the work and has estimates of the cost of clearing up her marsh land, which is not much less than the Newark area. The Kearny meadows at the junction of the Hackensack and Passaic are being filled by immense hydraulic dredges and will soon be not only mosquito free but industrially useful. At a number of other places in the state effective work has been done, and it is now all in the direction of permanent improvement. A
breeding place once eliminated makes a permanent reduction in the supply and is a positive gain.
By an amendment to the health laws passed during the session of 1904, waters in which mosquito larvæ breed are declared nuisances because of that fact alone, and the local boards of health are empowered to deal with them. In a number of places proceedings under this law have produced excellent results.
The investigations made are important as eliminating from consideration vast stretches of supposed breeding grounds like the cat-tail areas in the Hackensack Valley; as limiting the number of species which must be dealt with; as showing clearly the natural checks that may be practically utilized; as proving to demonstration that control amounting to practical extermination is not only possible, but not even difficult; and finally as furnishing a scientific basis for practical work.