i all INSECTS AND DISEASE veins extend to the margin of each wing; the top of the thorax does not have a distinct V-shaped suture near the middle; the costa (Fig. 14) continues around the hind margin of the wing; and the wing veins bear conspicuous, scale-like hairs. The Culicidae (Mosquitoes) are slender; they have long, slender, usually moderately hairy or scaly legs; their tibia (the second large joint of the legs) have apical spurs; the wings are elongate and narrow. The Psychodidzx (Mothflies) are small and robust; their legs are short and densely hairy; the tibia have no apical spurs; the wings are short, broad, and some: times pointed apically. The Simuliide and Ceratopogonide have more than four distinct longitudinal veins but less than nine veins extend to the margin of each wing, and the wings do not have a network of fine creases; the costal vein does not continue beyond the apex of the wing; and there are no ocelli (small, simple eyes which, when present, are situated between, often above, the conspicuous compound eyes). The Simuliide (Black-flies, etc.) are usually very small and thick-set; the antenne are shorter than the thorax; each antenna is composed of ten or eleven closely united segments, not plumose; the hind pair of legs are more or less dilated; the anterior veins of the wings are stout, the posterior ones weak. The Ceratopogonide (Punkies), like the Chironomidge with which they were formerly united but from which they have been separated because of their piercing mouth-parts, are slender delicate gnats; the antenne are slender, the joints more or less constricted and some: times plumose; the femora of the slender legs are sometimes thickened. General notions are not always safe guides in the classification of insects. However, our general notions as to what a mosquito is, combined with the discussion in the preceding paragraph, will probably suffice to enable us to recognize a culicid. No male of any species of Culicide ever “‘bites.’’ The females of most of the species with which we come in contact have the ability and desire to pierce the human skin with their needle-like mouths, if they get a chance, and to suck a small drop of blood. If this were all they did, it would be bad enough, but, when they pierce the skin, they inject an irritating substance, saliva, which sometimes “carries with it the microscopic, unicellular animals which cause malaria, and down this minute, microscopic [salivary] duct has flowed the fluid which has altered the fate of continents and played a conspicuous part in the destruction of the ancient civilizations of Greece and Rome” (Shipley).
AMERICAN MUSEUM GUIDE LEAFLETS Fig. 15. RESTING POSTURE OF CULEX (above) AND ANOPHELES (below) The disease-bearing and rest-disturbing habits of mosquitoes have led to a detailed and almost feverish study of their taxonomy. Species have been named and genera erected on the basis of characters which are very difficult for the non-professional to use. Formerly, the common species of true mosquitoes inhabiting the northern part of the United States were divided into two genera: Anopheles and Culex. As Anopheles contains the malarial mosquito 30 “~~
oo z 3 INSECTS AND DISEASE (or mosquitoes) it is the more important in the present connection, although not so numerous in species as the old, inclusive, Culex. Not all species of Anopheles have spotted wings, and not all spotted winged mosquitoes are Anopheles, but, for practical purposes and especially in the northeastern United States, we may say that mosquitoes with spots on their wings are Anopheles and that those with plain wings are something else. Furthermore, the adults of Anopheles are given to holding their beaks in a line with their bodies while Cu/ex points the beak downward at an angle to the body-line. One of the technical points used in identifying adults of Anopheles concerns the relative lengths of the palpi and beak. The palpi are delicate, thread-like organs, one on each side of the beak. In the male the palpi are more feathered than in the female; this is even more true of the antenne, or “‘feelers.’’ Both sexes of Anopheles have the palpi nearly, or quite, as long as the beak; the females, at least, of our other mosquitoes have the palpi relatively short, rarely exceeding half the length of the beak. If one extends the three first fingers, the middle finger may be taken to represent the mosquito’s beak and the other two fingers the pair of palpi of Anopheles. If, now, the first and ring fingers be bent at the end of the first joint, the three fingers, as viewed from above, may serve as a model of the relative lengths of the palpi and beak of the female Culex. In applying this test, be careful not to confuse the antenne with the palpi.
<e Z 7¢ ffl fi iA Al ‘lA, WV Fig. 16. RESTING POSTURE OF MOSQUITO LARVA; ANOPHELES (left); CULEX (right) Mosquito larve live only in water but the females of certain species display what might almost be called foresight; they lay their eggs on ground which will later become covered with water, as on the mud of low places along a salt-marsh. The most familiar mos- 31
_ AMERICAN MUSEUM GUIDE LEAFLETS — quito eggs are those of the rain-barrel species—eggs which are laid on end, side by side, in a boat-shaped mass on the surface of the water in barrels, tubs, and similar places. The eggs of Anopheles are laid singly but frequently they float close to each other, the floating being favored by special structures along their sides. The larva, or ‘“‘wriggler’’ which hatches from an egg of Anopheles has a very short breathing siphon on its back at the tail end. The larva is lighter than water; when feeding or at rest, it floats just below the surface and parallel to it; when disturbed it wriggles vigorously from side to side, the motion sometimes carrying it downward but more frequently sideways. When at the surface, the end of the breathing siphon pierces the “‘surface film,’’ opens up, and exposes the ends of the trachee, the tubes which convey air to all parts of the creature’s body. In order to feed on the microscopic plants and other organic material floating at the surface, the larva twists its neck until its mouth is on a line with its back. While there are other, more technical characters, it is sufficient to say that a mosquito larva which has a short, stubby breathing siphon, floats parallel with the surface of the water, and twists its head to feed is an Anopheles. The Culex larva floats at an angle with the surface as shown in Fig. 16, and has a relatively long breathing siphon.
As a young insect feeds, its flesh increases but its skin does not stretch sufficiently to accommodate the enlarging body. Therefore, the old skin is cast from time to time and a new, larger skin is formed. Finally there comes a time, as in the case of such insects as moths and beetles, which like the Diptera have a “‘complete metamorphosis,’ when there emerges from a larval skin something which is neither larva nor. adult, and which is called the pupa. The pupa of moths is, for the most part, immobile and frequently enclosed in a protective case, the “cocoon,” which is spun for it by the larva. The pupa of mosquitoes is active, but not so active as a larva, and it does not feed. It also differs from the larva in being hunched up instead of slender and in having a pair of breathing siphons on its thorax (the part of the body just back of the head) instead of a single siphon on the tail. The pupa of Anopheles closely resembles that of Culex, but the abdomen is more sharply curved and the breathing siphons are more dilated at the top and relatively shorter than in Culex. The adult mosquito finally emerges from a:split in the back of the cast pupal skin, which forms a miniature boat upon which the 32
=” INSECTS AND DISEASE adult may stand while stretching itself before it flies away to perpetuate its species, perhaps at the expense of ours. Studies on a common fresh-water mosquito (Culex pipiens) made at the American Museum showed that at 20° C. the cycle was completed in 19.6 days, at 25° in 11.7 days, and at 30° in 7.8 days. In the vicinity of New York City there are three fairly common species of Anopheles: punctipennis, crucians, and what was formerly called maculipennis, more recently quadrimaculatus, but which probably should be called guttulatus. Remembering Pope’s advice concerning the choice between the old and the new, we will use the name quadrimaculatus.
Anopheles punctipennis is ‘a medium sized dark brown mosquito with the upper surface of the thorax dark brown at the sides and with several narrow lines of yellowish gray hairs appearing as one broad gray stripe in the center. The beak and legs are unbanded; the wings densely clothed with black and yellow scales, two large black patches and two smaller ones on the front margin especially conspicuous. The abdomen is dark brown, profusely scattered with yellowish brown hairs’ (Smith). The other two species to be mentioned here have no whitish spot on the front margin of the wings.
Anopheles crucians ‘‘is brown, not quite as dark as punctipennis, with the thorax striped with grayish scales, the wing veins clothed with whitish and black scales, the black ones especially collected along the wing margin’ (Smith). The hindmost wing vein has three black spots separated by two yellowish-white ones. ‘This mosquito flies earlier in the evening and later in the morning than either punctipennis or quadrimaculatus, and has, for this reason, been called the Daylight Anopheles.
Anopheles quadrimaculatus may be recognized by the four small dark spots on each of its yellowish wings. It is the species usually thought of in connection with malaria in this country and it has been observed to breed in brackish water as well as fresh. Little need be said concerning the other mosquitoes of northern regions, in connection with disease. They are troublesome on account of their biting habit, and for the same reason they are to be looked on with suspicion since they may be the unknown carriers of some disease. The females have relatively short palpi and the larve relatively long breathing siphons. In the South, however, 33
AMERICAN MUSEUM GUIDE LEAFLETS there are certain very important species. Culex quinquefasciatus, also known as fatigans, extends as far north as Washington and St. Louis, its larvae replacing the northern p/piens in the rain-barrels. In both species the eggs are laid in boat-shaped masses floating on the surface of the water. The wings of both species are clear and both species have white cross-bands on the abdomen; these abdominal bands are joined to lateral spots in pipiens but separated from the lateral spots in quinquefasciatus.
Aédes calopus, formerly called Stegomyia fasciata, the Yellowfever Mosquito, is frequently carried by vessels into temperate regions but it has not succeeded in establishing itself there. The adult flies by day instead of by night. Aédes is a genus which is separated from Culex by characters rather difficult for the layman to make out. Some of our common salt-marsh mosquitoes are now put in this genus. The following list of characters will probably differentiate calopus from anything with which it is likely to be confused; the claws on the front and middle feet of the female are toothed; the joints of the black feet are white-ringed, but at the bases only; the beak of the female is not white-ringed; the thorax is not markedly paler than the abdomen and bears silvery-white lines in the pattern of a lyre, but no median white line; the abdomen has distinct, segmental white bands which are continuous across the abdomen; the wing-scales are narrow and mostly brown.
Howard and others, in their report on mosquitoes published by the Carnegie Institution, say concerning ca/opus: ‘““Under natural conditions the eggs are laid singly in small irregular groups some distance above the margin of the water..... The larve live in accumulations of water in artificial receptacles. From being originally a tree-hole-inhabiting species, it is now wholly domesticated, and its larva inhabits artificial accumulations of water either within houses or in the vicinity of human habitations. Occasionally the larve occur in holes in trees, but always in proximity to habitations. Goeldi has found the larve in water held by bromeliads, presumably near houses, and by the still folded leaves of banana plants. In the tropics the earthen jars in which drinking water is kept within dwellings are favorite breeding-places; the larve have the habit of keeping to the bottom, and, as these jars are never emptied, their presence is not even suspected. Water may be poured from the small earthen bottles used in hotels in the tropics, and, unless the bottle is quickly and completely emptied, the larve will remain 34
INSECTS AND DISEASE behind. Holy-water founts in churches are a favorite breeding-place. Out of doors the larve occur in tanks, barrels, rain-barrels, raintroughs and discarded bottles and tins. The larva, when suspended from the surface film, hang nearly perpendicular..... Unlike many other mosquitoes they (the adult females) emit no sound when about to bite. The male likewise persecutes man and this has led to a widely quoted statement of Ficalbi that it sucks blood; however, it does not pierce the skin but laps sweat from the surface and in this way causes some irritation.”
Several other families of nematocerous Diptera should be briefly mentioned on account of their blood-sucking habits. Psychodidae. Some of the characteristics of this family were siven on page 29. The most common—possibly the only—genus found in the vicinity of New York City is Psychoda. Its larve live in decaying vegetable matter, exuding sap, cow dung, and other moist excrementitious matter. The small, moth-like adults run well but fly weakly. They feed largely on nectar and rarely, if ever, ‘bite’ animals, although they. may sip fluids from wounds. In the tropics there is a genus, Phlebotomus, in which the species have the proboscis rather elongated and these do pierce the skin of man and other animals for the purpose of sucking blood. Some of these species are believed to be instrumental in the transmission of disease. Simuliidae. See page 29 for some of the characteristics of the family. The species have received various common names including “buffalo gnats,” “‘black-flies,’’ ‘“‘sand-flies’’ and ‘“‘turkey gnats.” The principal genus is Simulium and, although there are not many species, individuals sometimes occur in countless hordes. The larve live in running water, usually where the current is swiftest. There the larve sit on their tails catching for food the organic matter which the stream floats to them. They are often so numerous that the object on which they are gathered seems to be covered with moss. Unfortunately, the bite of the adult is not in proportion to its small size and when hundreds of bites are received in one day it is easy to believe the reports of deaths of both cattle and human beings from the bites alone. In addition to this, they have been suggested as possible carriers of anthrax to cattle and of pellagra to man. The Ceratopogonide were mentioned on page 29 because of their biting habits; they have not, as yet, been connected with any disease. The species of Culicoides are the blood-sucking ‘“‘punkies’’ or ‘‘no-see-ums.” The larve are aquatic.
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AMERICAN MUSEUM GUIDE LEAFLETS MOSQUITOES AND MALARIA Few diseases have, until recent times, seemed more mysterious than malaria. This malady was defined in Quain’s Standard Dictionary of Medicine as late as 1894 as “‘an earth-born poison, senerated in soils, the energies of which are not expended in the srowth and sustenance of healthy cultivated vegetation. By almost universal consent this poison is the cause of all the types of intermittent and remittent fevers, commonly called malarial, and of the degeneration of the blood and tissues resulting from long residence in places where this poison is generated.’
‘Malaria,’ the Encyclopedia continues, “‘has generally been said to be the product of heat, moisture and vegetable decomposition. The terms marsh miasm, and paludal fevers, long employed to distinguish the poison and the fevers to which it gives rise, mark the almost universal belief that the air of marshes alone is endowed with the power of generating them. That low, moist, and warm localities are generally noted as malarious, is indisputable. Marshes are not, as a rule, dangerous when abundantly covered with water; it is when the water level is lowered, and the saturated soil is exposed to the drying influence of a high temperature and the direct rays of the sun, that this poison is evolved in abundance. The production of malaria on a $reat scale in this way was seen in the district of Burdwan, in Bengal. ‘The soil is alluvial, but dry; and until within the last few years, Burdwan was more salubrius than the central or eastern districts of the lower Gangetic delta. The drainage of the district became obstructed by the silting up of its natural and artificial outlets, the result being a water-logged condition of the soil, the development of malaria, and an alarming increase in the death-rate. ‘‘Malaria is, however, generated under conditions apparently widely different from the above. When the British Army under Wellington was operating in Estremadura, the country was so arid and dry for want of rain, that the rivers and small streams were reduced to mere lines of widely detached pools; yet it was assailed by a remittent fever of such a destructive malignity that, says Ferguson, who records the fact, ‘the enemy and all Europe believed that the British host was extirpated.’ ”’ Again “‘The disturbance of soil that has long been fallow is often followed, both in hot and temperate climates, by the evolution of malaria. A familiar example was the prevalence of intermittent fever in Paris during the fortifications of the same city, in the reign of Louis Philippe, and on a larger scale in different parts of France when the railways were in process of construction.” 36