Chapter II: Part 2

There is, so far as is known, no satisfactory method of destroying mosquitoes in the adult state, so that in the war against this pest we must direct our efforts against the eggs and young. Herrick tells us that “the methods taken to destroy mosquitoes fall into three distinct classes; namely, the draining of bodies of water liable to contain eggs and wrigglers, the application of oil to bodies of water that cannot be drained and the introduction of fish into pools that cannot be drained or oiled.”

Probably the best way to rid one’s immediate vicinity of mosquitoes is to drain all marshes, pools and open receptacles. The drying up of a few acres of swamp land may cause a marked fall in the death-rate of an entire neighborhood, particularly in regions where malaria is prevalent. The exposure of open tanks, reservoirs and barrels in which stagnant water stands is no less than criminal in some parts of the South.

Very often, for economic reasons, it is not practical to drain a swamp or to eliminate open sewage ditches. In such cases we may take advantage of the fact that the larvae of mosquitoes do not breathe by gills, but are forced to come to the top for air. If ordinary kerosene oil is sprayed upon the surface of the water, it spreads to form a thin film which the larva cannot penetrate with their breathing tubes, and so are drowned. The kerosene also destroys the floating eggs, and kills the female mosquitoes as fast as they attempt to deposit. Crude petroleum has been used instead of kerosene, but it does not spread as well, and is very little cheaper. According to Herrick, one ounce of kerosene is enough for fifteen square feet of water surface, and half a teacupful is plenty for a barrel of water. The most convenient way to apply the oil to small pools and ditches is by means of a five-gallon tank carried knapsack fashion, with a short hose and nozzle. As the entire development of the mosquito from egg to laying female seldom requires more than eighteen or twenty days, it is best to use the oil once every two weeks during the mosquito season. It would seem that an easier way to get kerosene into the sewage ditches would be simply to pour it into the water closet, and this has proven successful in cases where there is little or no current; on the whole, however, the surface-spraying system is best.

Ornamental ponds and pools cannot be drained or sprayed with oil, and the same may be said of artificial ponds where domestic animals drink. In these cases the mosquito pest may be mitigated by introducing fish or other small creatures which feed upon the larvae. In Japan, and more recently in other countries, the goldfish has been found very satisfactory for this purpose. Various species of shiners, sunfish and top minnows have also been used. W. P. Seal, who has given a great deal of attention to this phase of the mosquito problem, states his results as follows: “The writer has come to the conclusion, after many experiments in small ponds, that a combination of the goldfish, which is ornamental and useful in the open water, the roach or shiner, which is a very active species, two small species of sunfish, which live among plants, and the top minnow would probably prove to be more effective in preventing mosquitoes breeding than any other fishes.”

Vernon Kellogg, Tillyard and others have studied the habits of dragonflies in this connection, and the latter particularly has emphasized their value as destroyers of mosquito larvae. He saw a single dragonfly larva eat sixty wrigglers in ten minutes, and captured an adult dragonfly which had over a hundred mosquitoes in its mouth--so many that the mouth could not be closed. “I believe that a successful checking of the mosquito pest in the ornamental waters of parks and gardens could be readily obtained by the introduction of dragonflies whose larvae, as well as the adults, would prey upon the nuisance.”

The use of wire screens to exclude flies and mosquitoes from dwellings is now well-nigh universal in most parts of the United States, although there are still many rural communities in the South in which it appears to be quite unknown. To keep out ordinary mosquitoes the wire should have at least fourteen meshes to the inch, and the yellow fever mosquito will pass through any screen which has less than eighteen meshes. It is practically impossible to fit screens and frames well enough to exclude all mosquitoes, but it is certainly better to contend with a few stray mosquitoes in a screened house than to do battle with the myriads of pests which swarm into an unscreened domicile. The fewer the bites one receives, the fewer the chances of being bitten by an infected mosquito; the fewer infected bites, the less severe the resulting illness will be.

In many Southern cities the use of bed nets of bobbinet or mosquito bar has now become quite general. There is usually a kind of wire frame over the bed, and the net is sometimes tucked under the mattress all round, while in other cases it is long enough to reach the floor on all sides. Many travelers who must visit small towns, where the hotel bed nets are lacking or unsatisfactory, carry their own nets, and set them up every night to suit their fancy. Dr. Ross says: “Perhaps our first and best defense against malaria lies in the habitual and scrupulous use of mosquito nets at night.... The first care of the resident in the tropics, of the traveler, the sportsman, the soldier, the miner, the clerk, should be for his mosquito net. Wherever he lives, wherever he goes, he should see that his mosquito net is with him, that it is in good order, and that it is properly arranged at bedtime.”

There are several chemical substances used in driving mosquitoes out of houses. One may rid a room of mosquitoes by the fumes of burning sulphur, but the gas often discolors articles painted with lead paint, and tarnishes gilt furniture and brass bedsteads. A vegetable powder sold as pyrethrum, buhach, or Persian insect powder is made of chrysanthemums, and is fairly effective when scattered about or blown into cracks and crevices. It may also be burned as a smudge, but the fumes are not as effective as those of sulphur. Many of the mosquitoes fall to the floor in a stupor, and must be gathered up and burned, as otherwise they will revive in an hour or so. Another fumigant much in favor in New Orleans is a mixture of carbolic acid and gum camphor, and is known as culicide. A heavy reddish liquid, it is evaporated by heating slightly over a gas burner or alcohol lamp. The mixture is inflammable but not explosive, and the fumes are not dangerous to human life.

Hunters and campers often smear their hands and faces with various substances supposed to discourage mosquitoes, oil of citronella being one of the most popular. Camphor, cedar oil, kerosene and mixtures of these substances in various proportions are also used, besides several patented smudges and ointments. I have tried several of these, but found them unsatisfactory. Tobacco-smoke helps a little sometimes, and is at least free from the unpleasant and even nauseating odors of the other mosquito repellants.

LIFE AMONG THE BEDBUGS

The bedbug (_Cimex lectularius_) has been known to man for a long time, and has probably, as Herrick remarks, “been man’s bedfellow as long as man has slept in beds,” if not longer. The ancient Romans were intimately acquainted with this insect, and Pliny recommends a mixture of macerated bedbugs in water as a cure for snake bites. It is common in all parts of the civilized world, and doubtless came to America with our sturdy fathers--even the Mayflower probably carried a full cargo of bedbugs. Like its relative the stink bug, _Cimex_ has a peculiar odor which is quite noticeable in small rooms where the insects are unusually abundant. The full-grown bedbug is a flat-bodied, mahogany-colored creature, with mouthparts admirably adapted to blood-sucking. It lives in beds, window casings, cracks in floors, etc., or in any article of furniture which affords a crevice large enough to contain it. What we know about the insect’s life history is mainly due to Marlatt, who did his work in 1896, and to Girault, who carried out some further investigations some ten years later. The eggs are very small, white and oval, and are, according to Herrick, “laid in batches of varying numbers in cracks and crevices in the bedsteads or other places where the bedbugs happen to be. The number of eggs deposited by a single female is not known. Southall, Riley, and others have made the common statement, probably not based on actual observation, that each female lays about four batches of fifty each during the season. Girault actually succeeded in obtaining 111 eggs from one well-fed female between June 17 and August 19. How many she had deposited previous to confinement for the experiment he was, of course, unable to say. Girault’s experience with this one bug indicates that the females may continue to lay eggs at different periods throughout the breeding season and that there is only one generation a year.”

The eggs hatch in about ten days, and the young bugs appear very much like their parents--bedbugs do not pass through larva and pupa stages like flies and mosquitoes. Bedbugs probably eat nothing but blood, and a young individual, if properly supplied with this food, reaches maturity in about six weeks, shedding their skins at least five times during the period of growth. It is said that the bug feeds but once between moults; if this is true the occupant of the bed must suffer at least five bites in order to rear a single bedbug to maturity. Bugs very much like _Cimex_ are found upon swallows, chimney swifts, pigeons and martins, and many people believe that genuine bedbugs are distributed by these birds, but this is probably not the case. True bedbugs have never been found upon them, and although the “bird bedbugs” are occasionally found in houses they do not seem to enter beds and bite human beings. Bedbugs have, however, been found in chicken houses, where they presumably bite chickens, so that there is nothing inherently unreasonable in the view that they may be distributed by birds.

The bedbug almost invariably lies hidden during the day, or as long as there is a bright light in the room. As soon as the light is turned off they sally forth to attack an exposed portion of the sleeper’s body. It seems that they are particularly likely to be secreted about the pillow, and as soon as the room is dark hit upon the neck as the most desirable and accessible part of the victim’s anatomy. Only one who has had personal experience in these matters can appreciate the vigor of the onslaught, and the astounding rapidity with which the enemy whisks out of sight the moment the light is flashed on. The bedbug’s bite is not poisonous, and the pain is probably due only to the puncture, but this is sufficient to cause considerable irritation and swelling.

Elie Metschnikoff, the author of that fascinating book entitled _The Nature of Man_, was the first to call attention to the bedbug’s possibilities as a carrier of disease germs. Bedbugs have been made, under laboratory conditions, to transmit typhoid and other fevers, and a tropical disease called _kala-azar_, but it has never been demonstrated that the bugs actually do, under ordinary conditions, play any part in the diffusion of these diseases. “Many writers and experimenters,” writes Herrick, “have labored hard to prove this insect guilty of graver offenses than that of simply stealing blood from human hosts. The most they have been able to do so far, however, is to show that in one case, at least, the bite of the bedbug formed a starting point for a case of bubonic plague. As a matter of fact, this is really a stronger indictment against the bedbug than, at first thought, might appear. The sores resulting from bedbug bites offer ideal points of entrance for disease-producing organisms and are a source of real danger. Actual and definite proof that the bedbug transmits disease is very difficult to obtain, but suspicion points strongly in that direction.... It is extremely desirable to avoid the bites of this insect if possible, especially in hotels where beds are occupied by so many different people; but this is very hard to do, in fact, almost impossible if one travels much.”

Luckily the bedbug is wingless, and therefore much easier to control than winged pests like the fly and mosquito. If _Cimex_ were able to fly there would be no keeping him out, as the newly hatched young could pass through practically any sort of screen. The use of metal bedsteads puts the bugs at a disadvantage because they afford fewer cracks and crevices than those built of wood. Boiling water poured into the crevices kills both eggs and bugs, but a more convenient method is to use an oil can or squirt-gun filled with gasoline, kerosene, turpentine or alcohol. The easiest way to rid a room completely of insects is to fumigate with hydrocyanic acid gas, made by pouring dilute sulphuric acid on potassium cyanide. This gas kills every living creature in the room, but it is dangerous in the hands of careless or thoughtless persons.

LICE, CRABS AND COOTIES

Lice have been associated with human beings as far back as our historical records go, and are mentioned in the writings of Aristotle, Herodotus and other ancient writers. Ordinarily cleanly and well-dressed people today would be horrified to find lice about their persons, as they are now confined to soldiers and others who do not keep their bodies and clothing clean, but a few hundred years ago, when everybody was dirty, they thought nothing of it. Samuel Pepys, an English diarist of the seventeenth century, made the following laconic entry in 1668: “Up betimes, finding our beds good, but lousy, which did make us merry,” and there are many other matter-of-fact references to these vermin in the literature of the period.

There are three common species, but they are all essentially alike in structure, being small, wingless and provided with piercing and sucking mouthparts. Schiödte describes the behavior of a louse on the back of his hand: “Scarcely does the abominable little monster feel the heat of the skin before it lays aside its former disheartened attitude, and begins to feel at ease, its antennae oscillate for joy, and it stretches all six legs complacently out from the body. But though the pleasure and surprise at the sudden transportation into congenial surroundings for the first moment eclipse everything else, hunger soon asserts its claim, sharpened as it is by the long fast, which has rendered its stomach and intestines quite transparent. The animal raises itself on its legs, walks a few steps, seeking and feeling its way with its antennae, while we follow it with a magnifier. Presently it stops, draws in its legs a little, arches its back, bends the head down toward the skin at an oblique angle, while it probes a small dark and narrow organ repeatedly forward, and draws it back through the fore end of the head; at last it stands still, with the point of the head firmly abutted against the skin.”

All three of our species are blood-suckers, and are strictly human parasites, being found only occasionally upon the bodies of animals other than man. It is said, however, that they are sometimes carried about by flies.

The head louse (_Pediculus capitis_) is usually found among the hairs on the head, occurring elsewhere only occasionally. The female is about one-twelfth of an inch long, while the male is only about one-half as large; both sexes are grayish in color, but it is said that this varies with the color of the host. Herrick quotes Murray to the effect that lice on West Africans are black, those on Chinese yellow, those on Hindoos smoky brown, and so on. The eggs are fastened to the hairs by a gelatinous secretion, and the female has been known to deposit at least fifty eggs in the course of a week. The period of incubation is usually five or six days, and the young louse reaches maturity in a fortnight. The movements and bites of these creatures are irritating in the extreme, and the sufferer is sure to scratch so incessantly that the scalp is always in an inflamed condition. The head louse is not known, however, to carry any disease-producing organism.

The best way to get rid of the head louse, according to a circular memorandum prepared under the direction of Surgeon General M. W. Ireland, of the United States army, is to “clip the hair of the head with a hair clipper and wash with a mixture of equal parts of kerosene and vinegar. This should be followed in a few hours with a bath of soap and hot water.... The hair should be caught in bags and burned. In order to reduce the liability to infestation, the hair should be kept close at all times.” Sulphur ointment may be used without sacrificing the hair, but it is not so effective as the kerosene mixture.

The body louse (_Pediculus corporis_), known also as the gray-back and the cootie, is somewhat larger than the head louse, and is usually of a dirty white color. These creatures dwell in the seams and folds of clothing, and are therefore known to some writers as _Pediculus vestimenti_. They are difficult to find and to dislodge, as they do not often cling long to the skin, but retire to their hiding places in the clothing as soon as their blood-sucking is done. The eggs are laid in the seams and wrinkles of the clothing, that made of wool being given the preference. When one has no opportunity to change or wash one’s clothes the pests become so abundant as to be quite unbearable. Soldiers, inmates of prison camps and such people are particularly liable to be abundantly supplied with body lice; they may pass from one person to another when the bodies are brought into actual contact, or one may become infested by sleeping in louse-ridden beds.

The Dutch scientist Leeuwenhoek, more than two hundred years ago, carried out some experiments which are pleasantly reviewed by Herrick: “Leeuwenhoek ... made an attempt to find out something definite about the life history and rate of development of the body louse. He did not believe the popular saying that a louse could become a grandfather in twenty-four hours. At first he thought of hiring some person to act as host for the lice. Later he changed his mind, overcame his own natural aversion to these pests, and enclosed two large females within a fine black stocking, the top of which he fastened tightly around his leg above the knee. Here he allowed the two lice to live for six days and obtain their sustenance from his leg. At the end of this period he removed the stocking and found fifty eggs around one of the females and forty eggs in another part of the stocking, evidently laid by the second female, which, however, had escaped. He wore the stocking for yet ten days, when on examination he found twenty-five young lice which so disgusted him and dampened his enthusiasm that he threw the whole thing into the street. Since Leeuwenhoek’s time the author is not aware that any scientist has ever tried in the same way to study the life history of these lice.”

Fig. III. Three kinds of Lice. A, the head louse, _Pediculus
capitis_; B, the body louse, gray-back, or cootie (_Pediculus
corporis_); C. the crab or crab louse, _Pediculus pubis_.
]

_Pediculus corporis_ is the only species of louse known to act as a carrier of disease. Its connection with typhus and trench fever is admirably described by Brues: “Typhus fever has been well-known for many years and regarded as a disease characteristic of filthy surroundings. During our own civil war it claimed many victims among the inmates of army prisons, and has been endemic though not very prevalent in many parts of the world in times of peace. Through the researches of Ricketts and others we now know that typhus is spread by the body louse and its epidemiology is at once made clear. When it broke out in Serbia in severe epidemic form, a knowledge of the method of its transmission made control possible, even under extremely difficult and unfavorable circumstances.

“Trench fever has attracted notice in the European war zones, to which it appears to be restricted so far as present knowledge extends. That it is a new disease is, however, without question an utterly unwarranted assumption, for it has undoubtedly been brought to Europe from some little-known quarter of the globe, unless it may have previously existed in Europe which does not appear probable. During the latter part of the war it was successively recognized as a distinct disease, suspected of association with the louse, and soon proved actually to be louse-borne. We now know that the disease is due to a living microorganism, probably of such small size that it cannot be recognized under the microscope. This virus is obtained by the lice with their meal of blood taken from an infected person. At least five days must elapse before the louse becomes capable of transmitting the disease, indicating that the organism must undergo a development of definite periodicity in the insect. If it is transferred to another person its bite is not or only rarely infectious, but its excrement contains the virus and if scratched into the skin, trench fever develops. Typhus fever is a very dangerous disease with a quite high death-rate, but trench fever is non-fatal and its importance in the war zones has been due to its great prevalence and the fact that persons afflicted with it are often incapacitated for long periods.”

As body lice do not cling to the body except when actually biting, it is a comparatively easy matter to get rid of them. One has only to bathe while his clothing is being steamed or soaked in gasoline. The United States Army set up delousing plants which were nothing but steam sterilizes on a large scale, and they proved very satisfactory.

The crab louse (_Pediculus pubis_) is short and stout-legged, whitish on the back, with a distinct reddish cast about the legs. It usually inhabits the hairy areas about the sex organs, clinging close against the skin, but is not uncommon in the armpits, and has been found upon practically every part of the body except the head. The eggs are attached to the hairs, like those of the head louse; they hatch in less than a week, and the young crab reproduces at an early age. This little pest multiplies much more rapidly than either of the other species, and is besides more easily transmitted from one person to another. Although the usual means of communication is direct bodily contact, as in the sexual embrace, it may be transmitted otherwise. The United States Army memorandum informs us that “this insect is transmitted mainly by contact in lodging houses, houses of prostitution, bathtubs, and perhaps occasionally from toilet seats.... Although the crab louse has not been shown to be a transmitter of disease, still it is very annoying, and its presence is a reflection on a man’s cleanliness.... The treatment for this condition is to shave the hair of the pubic region, axillae, chest and legs. This should be followed by an application of the kerosene and vinegar mixture, followed by a bath with soap and warm water.” The usual treatment among civilians is the application of a little mercurial or blue ointment.

OUR FRIEND THE COCKROACH

There are four common species of cockroaches in the United States, only one of which is native to this country. The American cockroach (_Periplaneta americana_) is the large winged species so common in the Middle and Southwestern states. They devour nearly any sort of food, and have been known to eat the corks out of bottles, while no less an authority than Vernon Kellogg says that some sailors in San Francisco sleep with gloves on to keep roaches from gnawing off their finger-nails. The German roach (_Ectobia germanica_), known also as the croton-bug, is common in the eastern part of the United States. It is the smallest species we have, being seldom more than five-eighths of an inch in length. For some reason or other these roaches are usually found about water pipes, and are not common in small communities which have no water systems. The Oriental cockroach (_Blatta orientalis_) is common also in England, and came to America with the early colonists, although it is supposed to have originated in Asia. It is larger and stouter than the croton-bug, and is dark brown or black in color. The males have short wings, but the females are wingless or practically so. The Australian roach (_Periplaneta australasiae_) is very much like the American variety, except for some yellow spots and bands on the thorax and shoulders. It is less common than any of the others, being found chiefly in the South.

The life histories of all four species are essentially identical. The eggs are not deposited singly, but in clusters enclosed in a horny capsule, the end of which may often be seen projecting from the abdomen of the female. The young roaches appear very much like their parents, but do not reach maturity for several months. The flat bodies of these insects allow them to crawl into small cracks in woodwork and furniture, and they usually remain hidden during the day, coming out at night to seek what they may devour. They are really scavengers, and under certain conditions may be useful in this capacity, but their omnivorous habits and the intolerable stench of their bodies and excreta make them the bane of the careful housewife.

“Cockroaches,” observes the indefatigable Herrick, “are among the most difficult to control of the household pests. They are difficult to reach because they are especially adapted with their thin, flat bodies for hiding away in inaccessible cracks, crevices and crannies. Moreover, they are wary and shy of all baits and traps. The croton-bug is the most difficult of all to get rid of. It seems to display more caution in avoiding traps and baits than most of the others, and as it increases faster, it becomes much more abundant.” Several traps have been devised and used with some measure of success, and roaches may often be killed by feeding them plaster of paris mixed with flour, or by exposing deep jars of stale beer, a delicacy in which they hasten to drown themselves. Herrick quotes Washburn to the effect that powdered borax scattered about the kitchen will clear a house of cockroaches. The best way to completely rid a house of these pests is to fumigate with hydrocyanic acid gas, made by pouring dilute sulphuric acid on potassium cyanide. But this method, as I have pointed out elsewhere in this booklet, is too dangerous for awkward or absent-minded people to experiment with.

CHIGGERS, TICKS AND FLEAS

The chigger (_Leptus irritans_) is not a true insect, but the immature form of a mite, related to the spiders. The eggs are laid upon the ground in the Spring, and when the young chigger hatches it climbs up a blade of grass and awaits the coming of some animal to which it can attach itself. At this time it is a very small red creature, barely large enough to be seen with the unaided eye. It clings to any moving object which presents itself--usually some passing insect, but quite frequently a bird or one of the higher animals. After having fed for a time upon the blood and juices of its mount, the chigger drops off and changes into the adult mite, which is not parasitic, but feeds largely upon plant lice.

Man’s contact with the chigger usually comes while walking through the grass and weeds to which they cling. They cannot bear direct sunlight, and are not common upon closely clipped lawns unless these are very densely shaded. The tiny tormenter passes through the finest of clothing--silk hosiery and underwear are no protection--and attaches itself to the skin, sucking blood and setting up a severe irritation by means of some poisonous secretion. The resultant itching is so intense that one cannot resist the temptation to scratch the affected parts, which may become infected and cause blood poisoning, and, according to Hamilton, erysipelas. Although the chigger is not known to disseminate any particular disease, it is an intolerable nuisance, and has spoiled many a vacation in the South.

Fig. IV. Some Common Cockroaches. A, Oriental cockroach (_Blatta
orientalis_), female. B, same, male. C, American cockroach
(_Periplaneta americana_). D, Australian cockroach (_Periplaneta
australasiae_).
]

Some persons avoid chiggers by wearing high boots, others, sprinkle sulphur in their stockings, while still others use various patent preparations both before and after the act. My own experience is that if, directly after coming in from the field, one changes to chigger-free clothing and rubs whiskey or gasoline upon the parts likely to be affected, the number of bites will be greatly decreased. Dr. Vernon C. Allison treats the inflamed areas with potassium permanganate, but I have had no satisfaction in the use of this remedy.

The fever tick (_Dermacentor venustus_) is the carrier of the disease known as Rocky Mountain spotted fever. This disease is now restricted to the Northwestern states, most of the cases occurring in Idaho and Montana. The life history of the tick is much like that of the chigger. Hatched from eggs on the ground, the young seed tick mounts a tall blade of grass or a weed and fastens upon the first animal which comes along. Forcing the hooked sucking beak into the flesh of the host, it sucks blood until it is full grown. Then it falls to the ground and reproduces, dying soon after this duty is done.

Brues describes the fever tick situation as follows: “The _Dermacentor_ ticks occur abundantly on various small wild mammals in the younger stages and as adults on domesticated animals, such as cattle, and from these become transferred to man. It has been experimentally shown that certain rodents are susceptible to the disease, and a tick thus infected in the nymphal stage can retain the disease organism until it becomes adult. It may then reach its human host through the medium of domesticated animals such as cattle. It appears that this is the ordinary way in which human cases have their origin, i. e., through the bite of adult ticks, although the newly hatched _seed ticks_ derived from eggs laid by infected mother ticks are known to contain the organism also.

“Although Rocky Mountain fever is of minor importance at the present, it is feared that it may increase its range at any time, since other ticks of wider distribution are apparently capable of acting as carriers. Whether this may happen is by no means certain, however, and the vigorous measures already undertaken to reduce the abundance of ticks on domesticated animals will undoubtedly bear fruit in the gradual reduction of this locally much-dreaded disease.”

There are many other species of ticks in the United States, but their life histories are all very similar. Several of them are believed to be carriers for various diseases of cattle, but _Dermacentor venustus_ is the only one known to distribute disease among human beings. The common Southern cattle-tick (_Margaropus annulatus_) is the sole carrier of the cattle disease known as Texas fever, which has caused a tremendous pecuniary loss in several of the Gulf States. The protozoan parasite which actually causes the trouble is called _Babesia bigemina_, and Brues refers to the tick’s “becoming infected during its period of engorgement when feeding on the blood of a diseased animal and then transmitting the _Babesia_ through its eggs to the young ticks of the next generation. These may feed on healthy animals the next season, conveying to them the parasites that have been handed down from the mother tick.”

Fig. V. Chiggers and Ticks. A, young and adult chigger (_Leptus
irritans_) redrawn from Herrick. B, Rocky Mountain spotted fever
tick, (_Dermacentor venustus_), after Brues. Male at left, unengorged
female at right.
]

Only two species of fleas are common in dwelling-houses in the United States. One is the human flea (_Pulex irritans_) and the other is _Ctenocephalus canis_, found almost universally upon cats and dogs. One must not suppose, however, that human fleas bite humans only, and that _Ctenocephalus_ confines its attention to dogs and cats; the human flea does not scruple on certain occasions of good omen to attack dogs, cats, rats and mice, while the various other species of fleas bite man also whenever the spirit moves them. The adult flea lives entirely upon the blood of its host, obtained through the admirable piercing and sucking mouthparts. The human flea, according to Herrick, is so bloodthirsty that it sucks regularly more blood than it can hold, and the surplus is seen squirting out of the anus while the creature is sucking more in at the mouth.

The eggs are dropped almost anywhere, and the tiny white larvae develop in cracks and crevices, feeding upon the organic matter in wood and rubbish. The pupa is enclosed in a silken cocoon, and the adult may appear in less than two weeks after the eggs are laid, although the period is usually somewhat longer.

Until comparatively recent years the flea was looked upon only as a nuisance, but it has now been discovered that some species act as agents in spreading bubonic plague, one of the most terrible scourges known to human history. It appears that the plague is primarily a rat-disease, and affects the human animal only incidentally. Outbreaks of plague among human beings are always preceded by an epidemic among the rats of the same region. The part placed by fleas in the matter is stated by Brues as follows: “The relation of the flea to the transmission of plague is due to the fact that rats are regularly infested by fleas that may become infected with the bacillus of plague, if it be present in the blood of the host upon which they are feeding. These bacilli remain in a viable condition for some time in the gut of the flea and may be transferred to a human subject bitten by an infected flea. Thus, when a rat dies of plague, its fleas leave it to search for a new host; if they attach themselves to a rat, that animal is liable to infection, or if they feed upon a human being, as they frequently do, the disease may become transferred to man.... The plague bacilli (_Bacillus pestis_) appear only in fleas that have bitten infected persons or rats twelve to twenty-six hours previous to death, for after this time the bacilli do not occur in the blood. The vitality and virulence of the bacilli are preserved for nearly a week at least and sometimes fully a month; and there is actually an increase in their number during the first few days. Infection from these insects may then occur through their bites, if they contain extremely virulent bacilli, but probably occurs more commonly by the insects being crushed _in situ_ after they have punctured the skin.”

From 300,000 to 400,000 cases of bubonic plague occur in India every year, and nearly half of them terminate fatally. Comparatively few cases have been reported from the United States in recent years, but in various places, San Francisco for example, only the most vigorous and persistent repressive warfare against rats and fleas have prevented what might have been very serious outbreaks.

Transcriber’s Note:

- Text that was in italics is enclosed by underscores (_italics_).

- Illustrations were moved to the ends of the paragraphs in which they originally appeared. Their original page numbers are in the list of illustrations. The list of illustrations was not present in the original text.

- Inconsistencies in hyphenation have been standardized.

- Minor punctuation errors have been changed without notice.

- Spelling was retained as in the original except for the following changes:

Page 2: “Our Friend the Cochroach” to “Our Friend the Cockroach”
Page 3: “Europe. Picture Thomas Aquinus” to “Europe. Picture Thomas
Aquinas”
Page 8: “During the Spanish-American war” to “During the
Spanish-American War”
Page 13: “an epidemic which occured” to “an epidemic which occurred”
Page 13: “contended that purulent opthalmia” to “contended that
purulent ophthalmia”
Page 14: “is practically no opthalmia” to “is practically no ophthalmia”
Page 14: “spread of Egyptian opthalmia” to “spread of Egyptian
ophthalmia”
Page 16: “destroyed by the housekeper’s” to “destroyed by the
housekeeper’s”
Page 20: “walls and fences. in” to “walls and fences. In”
Page 20: “and verandas, and is” to “and verandas, and it is”
Page 21: “Lucian Iches of Sante” to “Lucian Iches of Santa”
Page 22: “the province of Sante” to “the province of Santa”
Page 23: “inclines to be irridescent” to “inclines to be iridescent”
Page 25: “this habit of breding” to “this habit of breeding”
Page 27: “a single one developes” to “a single one develops”
Page 32: “The parasites reproduce sexually” to “The parasites
reproduce asexually”
According to other passages in the text, the parasite that causes
malaria reproduces asexually in the human body and sexually in
mosquitoes. This typo was corrected to make the text internally
consistent.
Page 35: “a field near Quemados” to “a field near Quemado”
Page 37: “is that the Aedes” to “is that the _Aedes_”
Page 42: “or Persian insect power” to “or Persian insect powder”
Page 47: “writings of Aristotle, Heroditus” to “writings of
Aristotle, Herodotus”
Page 47: “ease, its antennae oscilate” to “ease, its antennae
oscillate”
Page 48: “antennae, while we followed” to “antennae, while we follow”
Page 49: “is not known, howeve” to “is not known, however”
Page 54: “application of the kerosense” to “application of the
kerosene”
Page 60: “cattle, but _Dermacentor venusta_” to “cattle, but
_Dermacentor venustus_”
Page 63: “years the flea looked” to “years the flea was looked”