Popular Science Monthly/Volume 70/April 1907/The General Economic Importance of Mosquitoes

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THE GENERAL ECONOMIC IMPORTANCE OF MOSQUITOES[1]
By Professor JOHN B. SMITH

RUTGERS COLLEGE, NEW BRUNSWICK

NO one should be better qualified than a Jerseyman to speak on this subject, for no state in the union has suffered more in reputation and in arrested prosperity from mosquitoes than New Jersey.

During the four or five years last past, I have had opportunity to observe conditions closely, and there is not a section whose development has not been in some way affected by this insect pest.

First: by the carriage of malarial disease, and by the term carriage, I mean, of course, not the direct transmission from one individual to another, but that service as intermediate host in the development of the parasitic organisms that cause the disease.

Anopheles occurs throughout our state, although the A. maculipennis, which is the only one of our species known to be affected by the parasite, is comparatively rare and is, curiously enough, more abundant in the more northern, hilly portions than in the southern lowlands, where breeding places are more numerous.

Malarial diseases are much less common with us than they were a few years past, and that is due partially to the improvement of sanitary conditions which lessens mosquito breeding in densely populated districts, and partly to the much more thorough treatment which a patient now receives from the attending physician.

It requires the presence of a patient infested with the plasmodium, as well as of the proper species of Anopheles, to start an epidemic of malaria, but the mosquitoes need not be at all common to make trouble. I have in mind an instance very much in point: A village of high-class residences, well-located, generally healthy and where mosquitoes were accounted among the rarities; but, as it happened, the few that did occur were A. maculipennis. Into that community, where no case of malaria had ever been known, was introduced a gang of Italian laborers, recent immigrants, it was later found, and most of whom had been affected with the fever in Italy.

Before the end of the season a considerable number of cases of the æstivo-autumnal variety had developed in the village and some of them of the most severe type. This led to a search for the cause, and the breeding places for the few mosquitoes that occurred were located and abolished. Italian laborers have been tabooed in that locality since then, and for the two years last past no further case has developed, so far as I have been able to find.

The agency of mosquitoes in the transmission of other febrile diseases is so definitely established that their economic importance as a menace to public health can not be doubted. Their agency in a number of other diseases is suspected with good reason. In New Jersey a recent amendment to the general health law classifies 'waters in which mosquito larvæ breed' among the nuisances over which local boards of health have summary jurisdiction, and we have the fullest powers under our law for dealing with the mosquito pest. Action under those powers is not yet the rule, but each year sees a greater advance in this direction.

The great bulk of the mosquitoes occurring in this section of our country are not agents for the transmission of any disease known to us; but their attacks may be, and often are, so annoying as to form a positive injury to the health of weak or sickly individuals by robbing them of sleep and by the constant irritation of their bites. To some persons the bite of a mosquito is really a serious matter and severe swelling and inflammatory conditions are caused. To nobody is it a pleasure to be bitten, and there is no point of view from which the insect is not a detriment to health and the pursuit of happiness.

Second: the influence on the agricultural development of an infested area. This is a point that is rarely referred to, and it is not realized that the character of a farming district may be substantially modified by mosquitoes. Dairying, or supplying milk for the markets of New York, Philadelphia and our own cities, is a very important industry in New Jersey, and a large portion of the Philadelphia supply comes from the southern part of that state. We have a stretch of land in one of these southern counties eminently adapted for dairying, and where herds have been in times past established again and again; but they never lasted long, simply because the incessant attacks by swarms of mosquitoes reduce the yield as well as the quality of milk to such an extent as to make the animals unprofitable. It has been necessary to change the type of agriculture in these areas to a less profitable one simply because of the mosquito pest.

Another section of our state, not far from the shore, is peculiarly adapted to the growing of small fruits, particularly berries of various kinds. These are very profitable and find a ready sale in the near-by resorts. But just about the time when these berries ripen, the country is apt to be flooded with swarms of mosquitoes from the salt marshes, and when they do come it is impossible to get pickers. Gangs of Italians have been brought down from Philadelphia, they have started in blithely, and by noon have given up the work and started back to the city. Of course such conditions do not occur every year; nor do they continue throughout the season; but they do occur often enough and last long enough to make the farmer hesitate about putting in a crop which he knows would pay if he got it, but which he may be compelled to see rot on the ground because no pickers can be found to brave the mosquito hosts. Few persons are ready to believe at a first statement how important a factor in. the agricultural development of a region the mosquito may become.

Third: there is the effect of the mosquito upon the availability of a territory for development as a residential district.

This is the most important feature of the problem in New Jersey today, and there is no exaggeration in the statement that the elimination of the mosquito would add ten millions to the taxable value of real estate in two years. Let me illustrate: New York City is a highly desirable place of residence in winter; but less so in summer, and there are thousands of residents of New York City who are well able to afford a summer home within an hour or two from town, and who are quite willing to pay for it. New Jersey has many places ideal in situation and accessibility, and one such place developed rapidly to a certain point and there it stood, halted by the mosquitoes that bred in the surrounding marsh lands. Country club, golf, tennis and other attractions ceased to attract when attention was necessarily focussed on the biting or singing pests that intruded everywhere, and the tendency was to sell out. But the owners were not ready to quit without a fight, and an improvement society was formed which consulted with my office and followed my advice. In one year the bulk of the breeding area was drained, mosquitoes have since been absent almost entirely; one gentleman, not a large owner, either, told me his property had increased $50,000 in value, and new settlers began to come in. This year one of the worst breeding areas of the olden day was used as a camping ground, and 100 new residences are planned for next year.

New Jersey has miles of sea coast that is unequaled for summer resorts. All but a few points are practically abandoned as uninhabitable. Barnegat Bay and its surroundings constitute a fisherman's paradise, and again and again settlements have started, done well for a season and have been abandoned. Those who came one year never came again, and many who came for a month stayed only a day.

The only thing that prevents a continuous line of summer resorts along the entire shore line is the mosquito pest, and were that removed there would be a scramble to get land.

We may take the result on Staten Island as an example. This Island, now a part of Greater New York, is geographically a portion of New Jersey, separated from the mainland by a narrow stream or 'kill,' on both sides of which salt marsh flats extend for a mile or more to the highland. The southern and eastern shore is a continuation of the New Jersey coast line from the mouth of the Raritan River, and like it has a number of indentations more or less bordered by salt marsh areas. On all these marshes mosquitoes bred in uncounted millions and spread throughout the island. Result: several square miles of most desirable territory for suburban residences entirely unsettled. There are two shore resorts, South Beach and Midland Beach, feeble imitations of Coney Island in some directions, but more desirable in others, that just maintained themselves despite their attractions. During the day conditions were tolerable along shore, but as soon as the sun was low in the horizon trouble began, and as it became dusk the fight began, and pleasure seekers sought shelter behind screens or started for home.

This past summer, under the supervision of Dr. A. H. Doty, state quarantine officer, the salt marshes have been drained in the manner advocated by me, and the beginning was made on the eastern and southern shores, where Midland and South Beach are situated. I need hardly say that very few believed in good results, and scepticism was general even in circles where we might have expected material support But we got the needed money, secured a contractor within our estimate, and the eastern and southern shore work was done before the breeding season set in.

Result: there have been very few mosquitoes of any kind, and practically no marsh mosquitoes along this shore during the entire season. Visitors stayed longer and came more frequently to both beaches, which enjoyed a season of unparalleled prosperity, taxing the full capacity of the transportation companies. As the season advanced, the drainage work extended farther and farther away from the populated sections, permanent residents began to notice that nobody was putting in screens, and that screened porches were never used. On the golf links games could be carried on while the light lasted, and outdoor dinners and suppers became the rule at the Country Club. When it was fully realized that there was practically no mosquito pest, and the improvement in the character of the drained territory was obvious, there was a change in public sentiment. Plans were made for extending the attractions at the beaches, and many thousands will be put into new amusement enterprises during the present winter. Land values stiffened and very little was offered for sale.

Two industrial enterprises decided to locate on the marsh area On the west of the island, and these are expected to employ, respectively, 4,000, and 6,000 men, most of whom will undoubtedly settle near-by. These enterprises will result in actually reclaiming a large section of the marsh, which is something that mosquito drainage does not and was not intended to accomplish.

It is fair, therefore, to consider the mosquitoes of great economic importance, and as serious drawbacks to any community from three points of view:

First, their influence, direct and indirect, upon the health and well-being of the inhabitants.

Second, their influence upon the development of the agricultural resources, preventing or limiting the profitable use of infested territory for certain purposes.

Third, their influence upon land values due to the drawbacks mentioned under 1 and 2.

Having determined these points, it remains to determine whether, in any stage, any species of mosquito is of any value to man, directly or indirectly. The adult is a feeder upon juices of plants and animals; it produces nothing of use to us and removes nothing that is detrimental. It is of absolute importance to the continued existence of those microzoa that pass one stage of their existence in the mosquito body and nowhere else; but no one will argue that it is desirable to continue these organisms, and if the destruction of the mosquito is accompanied by the elimination of Plasmodia, Trypanosomes; Filaria and others of similar ills, a double good will have been accomplished.

In the larval stages the species are feeders upon the microorganisms, animal and vegetable, that occur in more or less stagnant waters. In a way they are scavengers, and it can not be definitely said that they may not destroy or limit some organisms that might otherwise be or become harmful to man. Could it be proved then that these stagnant water areas are necessary, it might be a question whether it is wise to war on mosquitoes until we have a more definite knowledge of the food of the wrigglers. But are these stagnant waters of any use to man, and is it necessary to retain them? On this point also it seems to me the answer must be against the insects, leaving absolutely no evidence that they are of any use or benefit whatever to the human race, directly or indirectly, as larva or adult.

The legislature and governor of New Jersey are sufficiently convinced of the injurious effects of the mosquito upon the development of the state to venture an investment of $350,000 in the effort to secure the practical elimination of the pest.

  1. Read at a meeting of the American Society of Tropical Medicine, Philadelphia, December 7, 1906, and published under its imprimatur.