Fighting Our Insect Enemies
( Originally Published 1917 )
Insect Carriers of Disease.—The third important way in which germs are carried from person to person is by means of flies, mosquitoes, and other insects.
The germs of some diseases may be carried by insects occasionally and accidentally, as in the case of the ordinary fly, which picks up infected matter on his feet and carries it to food. There are other diseases, like malaria and yellow fever, in which the germ actually grows and multiplies in the body of the insect. Most diseases of this last kind are spread by the bite of one particular insect and in no other way.
Plagues of Olden Times. In olden times when our great-great-great-grandfathers lived in conditions of filth that no one would think of enduring to-day, there were a great many more insect pests than there are at present. Perhaps the most terrible of all human diseases was the bubonic plague or Black Death, which swept over Europe in the fourteenth century and killed a quarter of the whole population. We now know that this is a disease of rats; the germ is carried from one rat to another, and finally from rats to men by the bites of fleas.
In 1894 there was an outbreak of bubonic plague in Asia, and since then the infection has been spread along the great highways of commerce all over the world, by the ships passing from one seaport to another. We have had single cases in San Francisco and New Orleans, and there have been others at various points from England to Australia and from China to Brazil. Yet nowhere outside of Asia has the disease made any headway, because at every seaport where it has appeared there has been a vigorous campaign against rats, which has stamped out the infection. At some seaports it was found that the rats passed to and from ships along the mooring hawsers, and this has been prevented by slipping wide collars along the hawsers, which block the progress of the rats.
Another terrible disease of olden times was typhus fever, sometimes called ship fever, or jail or camp fever, because it was so common under the unsanitary conditions of ships, jails, and army camps. The germ of this disease is carried from one person to another by the bite of the louse. With the better habits of personal cleanliness which prevail to-day, this disease had almost disappeared from civilized countries; but in 1915 the filthy conditions along the south-eastern battle front of the European war gave it a new chance to spread.
The Filthy Fly.—There are many different kinds of flies, but the commonest kind about our houses is the one which, on that account, is generally called the house fly. It ought not to be a house fly, and we intend that it shall soon cease to be a house fly. It always is and always will be a filth fly, however, for it breeds in filth, lives largely on filth, and carries filth wherever it goes.
The fly, like many other in-sects, goes through four stages in its life history. The mother fly lays her tiny white eggs in manure, garbage, or other refuse or decaying organic matter. From each egg hatches out a little white maggot or larva (lar'va) which grows for four or five days. It then burrows down into the ground and changes to a motionless resting stage, called the pupa, like the chrysalis of a butterfly or moth. After four or five days more, the adult fly comes out of the pupa and makes its way up to the air.
As the fly passes from the places where it breeds to our houses, and possibly to the dinner table, it carries all sorts of filth germs on its feet and body, and among them there may be disease germs too. If you let a fly walk over a bacterial culture plate,—a shallow dish containing a jelly on which germs can grow,—its path will be marked by colonies of bacteria which it has planted there. The dirtier the surroundings, the greater is likely to be the number of microbes carried by the fly. A bacteriologist collected some flies and washed off the germs on their bodies by shaking them in water. The average number of microbes per fly was over one million for flies from dirty places and only four-teen thousand for flies caught in clean places.
In the Spanish-American War, about one out of every five of our volunteer soldiers had typhoid fever, and it was found that the fly was one of the principal agents in spreading the disease. In Jacksonville, Florida, flies used to cause a great deal of typhoid, until a campaign for the screening of outside closets reduced the typhoid death rate of the city to less than one fourth of what it had been.
Typhoid fever is by no means the only disease that is carried by flies. Studies made by the Association for Improving the Condition of the Poor in New York City showed that babies which were carefully protected from flies had only one half as much diarrheal disease (summer complaint) as babies not protected in this way.
How to Fight against the Fly.—Flies are not only a nuisance, therefore, but a real danger to health.
There are four principal ways by which we may fight against them: by preventing their breeding, by trapping them, and by keeping them away from human discharges and from food. Anti-fly campaigns are becoming very popular in many places, and justly so. These campaigns, however, might sometimes be conducted so as to do much more good than they now accomplish. "Swatting" flies often has a prominent place in them, but "swatting" is a much less effective method than preventing the breeding of flies and trapping them.
Destroying the Fly's Breeding Places.—The first and most important thing to do in getting rid of flies is to prevent their breeding by taking care of the materials in which the maggots can grow. As manure is the fly's favorite breeding place, great pains should be taken, wherever there is a stable, to keep the manure in tight, dark, covered bins and to disinfect it with borax or hellebore to destroy the maggots. Another good way to keep manure is in a box with a perforated bottom, having a pan of water underneath. If the manure is kept moist, the maggots when full grown will go down in search of the earth, and crawling through the holes in the bottom will drop into the water, where they drown.
Manure is not the only breeding place of the fly; all sorts of decaying rubbish must be cleaned out from the yard and street, if the number of flies is to be reduced. The removal of such fly-breeding rubbish is one of the most important factors in an anti-fly or general "clean-up" campaign.
Trapping Flies.—Trapping the adult flies is also an important measure of control. The traps which are most effective consist of wire cones opening upward into wire cages. Some bait that will attract flies is placed under the lower wide opening of the cone, and the flies on leaving the bait will fly upward through the small end of the cone into the cage.
A description of a good fly trap and of the way in which any one can easily make such a trap is given at the end of this book (page 366).
Other Protections against Flies.—Cleaning up and trap-ping greatly reduce the number of flies, particularly if begun early in the season; but these measures will not destroy them entirely. It is important to prevent the remaining flies from carrying disease germs, by keeping them away from human discharges where they pick up such germs, and from food where they may deposit them. Out-side closets should be made tight and screened against flies, and the doors and windows of houses should be screened, especially in the kitchen and the dining room and in any room in which there is a case of sickness. Care should be taken to see that screens fit closely and that they are always in place, and that screen doors are not left ajar or held open. If wire screens cannot be provided, flies may be kept out by cotton mosquito netting tacked over the windows.
Mosquitoes and Malaria.—The name malaria means bad air, and not very many years ago it was thought that this disease was caused by some strange gas that rose from marshes or from places where the earth had been dug up. It was finally discovered that the cause of malaria is a germ which grows in the blood. This germ cannot get out of the body and be carried from one person to another in any direct . way, but only by the bite of a mosquito which has drawn the germ up through its sucking tube along with the blood it feeds upon. This discovery cleared up at last the mysterious connection between malaria and marshes and upturned soil. Mosquitoes breed in stagnant or slowly running water, and the reason why ditches and swamps favor malaria is that they furnish the water in which mosquitoes breed.
Curiously enough, there is only one kind of mosquito (the A noph' e les mosquito) in whose body the malarial germs will live long enough to be carried from one person to another. Mosquitoes, like flies, go through four distinct stages of growth, and in the second and fourth of these stages it is easy for any boy or girl to tell the malarial mosquito from the common kinds.
From the eggs laid by a mosquito on the surface of a pool or sluggish stream, there hatches out a little larva or wiggler, so called because it jerks about in the water in which it lives and grows. If there are mosquitoes about your house or school, a little observation will soon show you where they are breeding. The little blackish wigglers, about three eighths of an inch long, are generally collected at the surface. When they are quiet, the wigglers of the common mosquito (Culex) rest at an angle with the surface, and those of the malarial mosquito (Anopheles) rest flat against it. If you dip up some water from a pool or stream in a white cup and find little wigglers like the picture, you may be sure that mosquitoes are breeding there. After a week or so the larvae change to curiously shaped pup, and in a few days more these pupae hatch out into adult mosquitoes, which emerge from the pupa cases floating on the surface of the water and, after strengthening their wings for a few moments, fly away.
The common mosquito, when full grown, rests in a sort of humpbacked position more or less parallel with the wall on which it is standing, while the malarial mosquito stands out from the wall in a nearly straight line (see Fig. io8). You can also tell the malarial mosquito by the fact that it has spotted wings.
How to Control Mosquitoes.—The way to control the breeding of mosquitoes is to drain or fill in small pools, clear the channels of sluggish, weedy streams, and empty barrels, pails, tin cans, and everything else containing stagnant water in which the insects may breed. If a pool cannot be got rid of, mosquito breeding can be prevented by pouring a little kerosene or crude oil on the water every two weeks. The oil spreads out in a thin layer on the surface and kills the larval mosquitoes because the' wigglers must come up to the surface to breathe, and if the surface is covered with oil they cannot get their breathing tubes through it to reach the air.
Fish, frogs, and some of the larger water insects eat a good many mosquito wigglers. A pool that is too pretty to be drained or oiled is often stocked with fish to prevent mosquitoes from breeding.
Houses in malarial regions should be carefully screened, and beds protected by netting. Particular care should be taken to avoid letting Anopheles mosquitoes bite malarial patients and thus acquire the infection which they may carry to others.
School Sanitary Squads.--In many schools, Health Leagues or Sanitary Squads have been organized to work under the direction of one of the teachers, the school physician, or the school nurse. Their task is to study and improve the sanitary condition of the school building and grounds.
Such a Sanitary Squad can do real service by inspecting the surroundings of the school to see where insect pests are breeding. They can soon learn to recognize fly maggots and mosquito wigglers, both the common and the malarial kind. Once the breeding places are found, it is generally easy, by cleaning up or oiling, or by some of the other ways described above, to get rid of most of these dangerous pests.
The Health Leagues should meet at regular intervals for talks by teachers, health officers, or public-spirited physicians, in regard to the sanitary problems of the school and the community. They may select their own officers and provide for and appoint, with the approval of the teacher, committees on heating and ventilation, water supply, toilet facilities, school grounds, flies, and mosquitoes.
The war against insect pests requires keenness, patience, ingenuity, and real scouting work to find the enemy. It is civic service of the right sort, for every campaign against these pests is a part of the great defensive war of humanity against disease.
Committees of the Health League.—A Committee on Heating and Ventilation should be formed, including a health officer in each classroom. His work is to read the thermometer at regular hours each day for a certain period and chart the readings on a blackboard space reserved for the purpose, where pupils, principal, janitor, and visitors can see a week's record at a glance. It is the duty of this committee, when conditions permit, to readjust heat sources, ventilators, or windows to secure proper temperature, which, when artificial heat is used, should never exceed 68° Fahrenheit. Older boys may make observations of humidity, dust, and air currents.'
A Committee on Water Supply should study the source of water supply in use by the school or the community, in the light of instruction given at one of the meetings of the League; and should be charged particularly with the duty of observing and guarding against the use of common drinking cups.
A Committee on Toilet Facilities is charged with super-vision of the cleanliness of toilet apartments. Washing facilities and the danger of the common towel fall within the scope of this committee's work.
A Committee on School Grounds is responsible for the general neatness of the school yard and surroundings.
It is the duty of a Committee on Fly Prevention to make a careful study of neighboring rubbish heaps in order to find out where the maggots are breeding. Boys who are clever at carpentry can build fly traps for the school yard and schoolrooms.
A Committee on Mosquito Control undertakes to locate the breeding places of mosquitoes; and the older boys may perhaps be intrusted with the periodic oiling of the breeding pools.
The Conquest of Tropical Disease.—In warm countries there are a great many insect-borne diseases, and their control since the beginning of the twentieth century is the most brilliant chapter in the history of public health. One of the first and most important steps in this great task, the discovery of the transmission of yellow fever by the mosquito, was made by four American army surgeons. The story is such a splendid one that all American children should know it.
These four men, Doctors Reed, Carroll, Lazear, and Agramonte, were sent to Cuba in 1900 to study yellow fever,
which had been killing seven hundred and fifty people a year in the city of Havana and was spreading among our soldiers. The investigators suspected a certain mosquito as a possible cause. They could not experiment with animals, because only human beings have yellow fever. So they tested their theory by allowing themselves to be bitten by mosquitoes which had bitten yellow fever patients. Carroll was the first to be successfully infected with the disease in this way. He came down with yellow fever and was very ill, but finally recovered. Lazear was the next to come down, and he died. Yet the experiments went on, and there was never lack of volunteers from the army to take this terrible risk.
Besides the physicians, the first volunteers to offer them-selves were two men in the government service, one a soldier and the other a civilian,—Kissinger and Moran. The only stipulation they made was that they should receive no pay, since they were performing this service for the sake of humanity. Major Reed, when they made this offer, touched his cap and said, " Gentlemen, I salute you."
Both Kissinger and Moran were exposed to the bites of infected mosquitoes and came down with the disease. Kissinger was the first of the non-medical volunteers to be experimented on. Of him Dr. Reed wrote, "In my opinion this exhibition of moral courage has never been surpassed in the annals of the army of the United States." Both of these men recovered, but Kissinger ten years later was awarded a pension from Congress for hopeless physical disabilities resulting from the experiments.
By March, 1901, this gallant band of investigators was able to announce that yellow fever was spread by the bite of a certain mosquito, and in no other way. At once an active campaign was begun against this particular insect, and the result was that there were only eighteen deaths from yellow fever in Havana that year, and none at all in 1902. The terrible disease which had cursed the city for half a century was wiped out in a single year.
Heroes of Science.—The history of medicine and public health is full of examples of quiet, unnoticed heroism, such as that which occurred at Havana. Howard T. Ricketts of Chicago was a brilliant young American investigator who gave his life in the fight against insect-borne disease. He died of typhus while studying its control in Mexico. Fifteen or more members of the United States Public Health Service have lost their lives in the course of their studies and as a result of them.
The Building of the Panama Canal.—It was the discovery made by Major Reed and his associates, with other discoveries in regard to insect-borne diseases, that made possible the building of the Panama Canal. The Isthmus of Panama was one of the most notorious plague spots in the world, and it was disease rather than engineering difficulties that drove the French back when they attempted to build a canal across it.
When the United States began its work, Colonel W. C. Gorgas, fresh from the fight against yellow fever at Havana, was placed in charge of the sanitary part of the undertaking. He began a campaign against mosquitoes similar to that which had been so successful in Cuba. He had to overcome the opposition of those who looked upon the mosquito theory as an impractical one, but his success was immediate as soon as he was allowed to deal with the yellow fever problem in the way which the Havana experiments had indicated. So successfully did his sanitary army ditch, drain, and oil, remove mosquito breeding places, and destroy adult mosquitoes, that yellow fever has been abolished on the Isthmus, and malaria reduced to a low figure. The completed Canal stands as a triumph of American engineering, and as an even greater triumph of American public health science.
QUESTIONS FOR DISCUSSION AND REVIEW
1. Compare the history of plagues in the fourteenth and in the nineteenth centuries. What was the difference?
2. How is the bubonic plague carried? By what measures may it be controlled?
3. What conditions existed in 1915, on the southeastern battle front in Serbia, which would cause such a disease as typhus fever to spread?
4. What are the different life stages of a fly? When is the best time in the life of a fly to destroy it?
5. What diseases are frequently carried by flies?
6. In what different ways can we fight the fly?
7. Jenny left her baby brother's carriage standing for a long time outside a badly kept stable. Was this dangerous? Why?
8. How should manure be kept? How may fly maggots be killed?
9. Explain the working of a trap like the one described in the Appendix (page 366). Make one like it, if you can.
10. Compare the life stages of the mosquito with the life stages of the fly.
11. Why did people think that malaria came from swamp gas? How is malaria carried from one person to another? What connection has this with marshy land?
12. How do mosquitoes breed? Where are the eggs laid? How may the eggs and wigglers be destroyed?
13. John found an old rain barrel swarming with mosquito wigglers. There were none in a goldfish pond near by. What is the probable explanation?
14. How could you organize a Sanitary Squad or Health League in your school? What work could you find for this League to do?
15. What health conditions were found in Cuba when our soldiers went there during the Spanish-American War? What was done to remedy these conditions?
16. Which do you think requires the finer courage: going into battle, or offering yourself for such a scientific research experiment as is described on page 274? Which is of greater service to the world?
17. Tell the story of the Sanitary Campaign in Panama. Even if our engineers had been no more skillful than the French engineers, why would we have succeeded in building the canal when they failed?