Chapter 2: 20 (3)

The culices of South America have generally the wings, corslet, and legs of an azure colour, ringed and variegated with a mixture of spots of metallic lustre. Here as in Europe, the males, which are distinguished by their feathered antennae, are extremely rare; you are seldom stung except by females. The preponderance of this sex explains the immense increase of the species, each female laying several hundred eggs. In going up one of the great rivers of America, it is observed, that the appearance of a new species of culex denotes the proximity of a new stream flowing in. I shall mention an instance of this curious phenomenon. The Culex lineatus, which belongs to the Cano Tamalamec, is only perceived in the valley of the Rio Grande de la Magdalena, at a league north of the junction of the two rivers; it goes up, but scarcely ever descends the Rio Grande. It is thus, that, on a principal vein, the appearance of a new substance in the gangue indicates to the miner the neighbourhood of a secondary vein that joins the first.

On recapitulating the observations here recorded, we see, that within the tropics, the mosquitos and zancudos do not rise on the slope of the Cordilleras* toward the temperate region, where the mean heat is below 19 or 20 degrees (* The culex pipiens of Europe does not, like the culex of the torrid zone, shun mountainous places. Giesecke suffered from these insects in Greenland, at Disco, in latitude 70 degrees. They are found in Lapland in summer, at three or four hundred toises high, and at a temperature of 11 or 12 degrees.); and that, with few exceptions, they shun the black waters, and dry and unwooded spots.* (* Trifling modifications in the waters, or in the air, often appear to prevent the development of the mosquitos. Mr. Bowdich remarks that there are none at Coomassie, in the kingdom of the Ashantees, though the town is surrounded by marshes, and though the thermometer keeps up between seventeen and twenty-eight centesimal degrees, day and night.) The atmosphere swarms with them much more in the Upper than in the Lower Orinoco, because in the former the river is surrounded with thick forests on its banks, and the skirts of the forests are not separated from the river by a barren and extensive beach. The mosquitos diminish on the New Continent with the diminution of the water, and the destruction of the woods; but the effects of these changes are as slow as the progress of cultivation. The towns of Angostura, Nueva Barcelona, and Mompox, where from the want of police, the streets, the great squares, and the interior of court-yards are overgrown with brushwood, are sadly celebrated for the abundance of zancudos.

People born in the country, whether whites, mulattoes, negroes, or Indians, all suffer from the sting of these insects. But as cold does not render the north of Europe uninhabitable, so the mosquitos do not prevent men from dwelling in the countries where they abound, provided that, by their situation and government, they afford resources for agriculture and industry. The inhabitants pass their lives in complaining of the insufferable torment of the mosquitos, yet, notwithstanding these continual complaints, they seek, and even with a sort of predilection, the commercial towns of Mompox, Santa Marta, and Rio de la Hacha. Such is the force of habit in evils which we suffer every hour of the day, that the three missions of San Borja, Atures, and Esmeralda, where, to make use of an hyperbolical expression of the monks, there are more mosquitos than air,* (* Mas moscas que aire.) would no doubt become flourishing towns, if the Orinoco afforded planters the same advantages for the exchange of produce, as the Ohio and the Lower Mississippi.

It is a curious fact, that the whites born in the torrid zone may walk barefoot with impunity, in the same apartment where a European recently landed is exposed to the attack of the nigua or chegoe (Pulex penetrans). This animal, almost invisible to the eye, gets under the toe-nails, and there acquires the size of a small pea, by the quick increase of its eggs, which are placed in a bag under the belly of the insect. The nigua therefore distinguishes what the most delicate chemical analysis could not distinguish, the cellular membrane and blood of a European from those of a creole white. The mosquitos, on the contrary, attack equally the natives and the Europeans; but the effects of the sting are different in the two races of men. The same venomous liquid, deposited in the skin of a copper-coloured man of Indian race, and in that of a white man newly landed, causes no swelling in the former, while in the latter it produces hard blisters, greatly inflamed, and painful for several days; so different is the action on the epidermis, according to the degree of irritability of the organs in different races and different individuals!

I shall here recite several facts, which prove that the Indians, and in general all the people of colour, at the moment of being stung, suffer like the whites, although perhaps with less intensity of pain. In the day-time, and even when labouring at the oar, the natives, in order to chase the insects, are continually giving one another smart slaps with the palm of the hand. They even strike themselves and their comrades mechanically during their sleep. The violence of their blows reminds one of the Persian tale of the bear that tried to kill with his paw the insects on the forehead of his sleeping master. Near Maypures we saw some young Indians seated in a circle and rubbing cruelly each others' backs with the bark of trees dried at the fire. Indian women were occupied, with a degree of patience of which the copper-coloured race alone are capable, in extracting, by means of a sharp bone, the little mass of coagulated blood that forms the centre of every sting, and gives the skin a speckled appearance. One of the most barbarous nations of the Orinoco, that of the Ottomacs, is acquainted with the use of mosquito-curtains (mosquiteros) woven from the fibres of the moriche palm-tree. At Higuerote, on the coast of Caracas, the copper-coloured people sleep buried in the sand. In the villages of the Rio Magdalena the Indians often invited us to stretch ourselves as they did on ox-skins, near the church, in the middle of the plaza grande, where they had assembled all the cows in the neighbourhood. The proximity of cattle gives some repose to man. The Indians of the Upper Orinoco and the Cassiquiare, seeing that M. Bonpland could not prepare his herbal, owing to the continual torment of the mosquitos, invited him to enter their ovens (hornitos). Thus they call little chambers, without doors or windows, into which they creep horizontally through a very low opening. When they have driven away the insects by means of a fire of wet brushwood, which emits a great deal of smoke, they close the opening of the oven. The absence of the mosquitos is purchased dearly enough by the excessive heat of the stagnated air, and the smoke of a torch of copal, which lights the oven during your stay in it. M. Bonpland, with courage and patience well worthy of praise, dried hundreds of plants, shut up in these hornitos of the Indians.

These precautions of the Indians sufficiently prove that, notwithstanding the different organization of the epidermis, the copper-coloured man, like the white man, suffers from the stings of insects; but the former seems to feel less pain, and the sting is not followed by those swellings which, during several weeks, heighten the irritability of the skin, and throw persons of a delicate constitution into that feverish state which always accompanies eruptive maladies. Whites born in equinoctial America, and Europeans who have long sojourned in the Missions, on the borders of forests and great rivers, suffer much more than the Indians, but infinitely less than Europeans newly arrived. It is not, therefore, as some travellers assert, the thickness of the skin that renders the sting more or less painful at the moment when it is received; nor is it owing to the particular organization of the integuments, that in the Indians the sting is followed by less of swelling and inflammatory symptoms; it is on the nervous irritability of the epidermis that the acuteness and duration of the pain depend. This irritability is augmented by very warm clothing, by the use of alcoholic liquors, by the habit of scratching the wounds, and lastly, (and this physiological observation is the result of my own experience,) that of baths repeated at too short intervals. In places where the absence of crocodiles permits people to enter a river, M. Bonpland and myself observed that the immoderate use of baths, while it moderated the pain of old stings of zancudos, rendered us more sensible to new stings. By bathing more than twice a day, the skin is brought into a state of nervous irritability, of which no idea can be formed in Europe. It would seem as if all feeling were carried toward the integuments.

As the mosquitos and gnats pass two-thirds of their lives in the water, it is not surprising that these noxious insects become less numerous in proportion as you recede from the banks of the great rivers which intersect the forests. They seem to prefer the spots where their metamorphosis took place, and where they go to deposit their eggs. In fact the wild Indians (Indios monteros) experience the greater difficulty in accustoming themselves to the life of the missions, as they suffer in the Christian establishments a torment which they scarcely know in their own inland dwellings. The natives at Maypures, Atures, and Esmeralda, have been seen fleeing to the woods, or, as they say, al monte, solely from the dread of mosquitos. Unfortunately, all the Missions of the Orinoco have been established too near the banks of the river. At Esmeralda the inhabitants assured us that if the village were situated in one of the five plains surrounding the high mountains of Duida and Maraguaca, they should breathe freely, and enjoy some repose. The great cloud of mosquitos (la nube de moscas) to use the expression of the monks, is suspended only over the Orinoco and its tributary streams, and is dissipated in proportion as you remove from the rivers. We should form a very inaccurate idea of Guiana and Brazil, were we to judge of that great forest four hundred leagues wide, lying between the sources of the Madeira and the Lower Orinoco, from the valleys of the rivers by which it is crossed.

I learned that the little insects of the family of the nemocerae migrate from time to time like the alouate monkeys, which live in society. In certain spots, at the commencement of the rainy season, different species appear, the sting of which has not yet been felt. We were informed at the Rio Magdalena, that at Simiti no other culex than the jejen was formerly known; and it was then possible to enjoy a tranquil night's rest, for the jejen is not a nocturnal insect. Since the year 1801, the great blue-winged gnat (Culex cyanopterus) has appeared in such numbers, that the poor inhabitants of Simiti know not how to procure an undisturbed sleep. In the marshy channels (esteros) of the isle of Baru, near Carthagena, is found a little white fly called cafafi. It is scarcely visible to the naked eye, and causes very painful swellings. The toldos or cottons used for mosquito-curtains, are wetted to prevent the cafafi penetrating through the interstices left by the crossing threads. This insect, happily rare elsewhere, goes up in January, by the channel (dique) of Mahates, as far as Morales. When we went to this village in the month of May, we found there cimuliae and zancudos, but no jejens.

The insects most troublesome at Orinoco, or as the Creoles say, the most ferocious (los mas feroces), are those of the great cataracts of Esmeralda and Mandavaca. On the Rio Magdalena the Culex cyanopterus is dreaded, particularly at Mompox, Chiloa, and Tamalameca. At these places this insect is larger and stronger, and its legs blacker. It is difficult to avoid smiling on hearing the missionaries dispute about the size and voracity of the mosquitos at different parts of the same river. In a region the inhabitants of which are ignorant of all that is passing in the rest of the world, this is the favourite subject of conversation. "How I pity your situation!" said the missionary of the Raudales to the missionary of Cassiquiare, at our departure; "you are alone, like me, in this country of tigers and monkeys; with you fish is still more rare, and the heat more violent; but as for my mosquitos (mias moscas) I can boast that with one of mine I would beat three of yours."

This voracity of insects in certain spots, the fury with which they attack man,* (* This voracity, this appetite for blood, seems surprising in little insects, that live on vegetable juices, and in a country almost entirely uninhabited. "What would these animals eat, if we did not pass this way?" say the Creoles, in going through countries where there are only crocodiles covered with a scaly skin, and hairy monkeys.) the activity of the venom varying in the same species, are very remarkable facts; which find their analogy, however, in the classes of large animals. The crocodile of Angostura pursues men, while at Nueva Barcelona you may bathe tranquilly in the Rio Neveri amidst these carnivorous reptiles. The jaguars of Maturin, Cumanacoa, and the isthmus of Panama, are timid in comparison of those of the Upper Orinoco. The Indians well know that the monkeys of some valleys are easily tamed, while others of the same species, caught elsewhere, will rather die of hunger than submit to slavery.* (* I might have added the example of the scorpion of Cumana, which it is very difficult to distinguish from that of the island of Trinidad, Jamaica, Carthagena, and Guayaquil; yet the former is not more to be feared than the Scorpio europaeus (of the south of France), while the latter produces consequences far more alarming than the Scorpio occitanus (of Spain and Barbary). At Carthagena and Guayaquil, the sting of the scorpion (alacran) instantly causes the loss of speech. Sometimes a singular torpor of the tongue is observed for fifteen or sixteen hours. The patient, when stung in the legs, stammers as if he had been struck with apoplexy.)

The common people in America have framed systems respecting the salubrity of climates and pathological phenomena, as well as the learned of Europe; and their systems, like ours, are diametrically opposed to each other, according to the provinces into which the New Continent is divided. At the Rio Magdalena the frequency of mosquitos is regarded as troublesome, but salutary. These animals, say the inhabitants, give us slight bleedings, and preserve us, in a country excessively hot, from the scarlet fever, and other inflammatory diseases. But at the Orinoco, the banks of which are very insalubrious, the sick blame the mosquitos for all their sufferings. It is unnecessary to refute the fallacy of the popular belief that the action of the mosquitos is salutary by its local bleedings. In Europe the inhabitants of marshy countries are not ignorant that the insects irritate the epidermis, and stimulate its functions by the venom which they deposit in the wounds they make. Far from diminishing the inflammatory state of the skin, the stings increase it.

The frequency of gnats and mosquitos characterises unhealthy climates only so far as the development and multiplication of these insects depend on the same causes that give rise to miasmata. These noxious animals love a fertile soil covered with plants, stagnant waters, and a humid air never agitated by the wind; they prefer to an open country those shades, that softened day, that tempered degree of light, heat, and moisture which, while it favours the action of chemical affinities, accelerates the putrefaction of organised substances. May not the mosquitos themselves increase the insalubrity of the atmosphere? When we reflect that to the height of three or four toises a cubic foot of air is often peopled by a million of winged insects,* (* It is sufficient to mention, that the cubic foot contains 2,985,984 cubic lines.) which contain a caustic and venomous liquid; when we recollect that several species of culex are 1.8 lines long from the head to the extremity of the corslet (without reckoning the legs); lastly, when we consider that in this swarm of mosquitos and gnats, diffused in the atmosphere like smoke, there is a great number of dead insects raised by the force of the ascending air, or by that of the lateral currents which are caused by the unequal heating of the soil, we are led to inquire whether the presence of so many animal substances in the air must not occasion particular miasmata. I think that these substances act on the atmosphere differently from sand and dust; but it will be prudent to affirm nothing positively on this subject. Chemistry has not yet unveiled the numerous mysteries of the insalubrity of the air; it has only taught us that we are ignorant of many things with which a few years ago we believed we were acquainted.

Daily experience appears in a certain degree to prove the fact that at the Orinoco, Cassiquiare, Rio Caura, and wherever the air is very unhealthy, the sting of the mosquito augments the disposition of the organs to receive the impression of miasmata. When you are exposed day and night, during whole months, to the torment of insects, the continual irritation of the skin causes febrile commotions; and, from the sympathy existing between the dermoid and the gastric systems, injures the functions of the stomach. Digestion first becomes difficult, the cutaneous inflammation excites profuse perspirations, an unquenchable thirst succeeds, and, in persons of a feeble constitution, increasing impatience is succeeded by depression of mind, during which all the pathogenic causes act with increased violence. It is neither the dangers of navigating in small boats, the savage Indians, nor the serpents, crocodiles, or jaguars, that make Spaniards dread a voyage on the Orinoco; it is, as they say with simplicity, "el sudar y las moscas," (the perspiration and the flies). We have reason to believe that mankind, as they change the surface of the soil, will succeed in altering by degrees the constitution of the atmosphere. The insects will diminish when the old trees of the forest have disappeared; when, in those countries now desert, the rivers are seen bordered with cottages, and the plains covered with pastures and harvests.

Whoever has lived long in countries infested by mosquitos will be convinced, as we were, that there exists no remedy for the torment of these insects. The Indians, covered with anoto, bolar earth, or turtle oil, are not protected from their attacks. It is doubtful whether the painting even relieves: it certainly does not prevent the evil. Europeans, recently arrived at the Orinoco, the Rio Magdalena, the river Guayaquil, or Rio Chagres (I mention the four rivers where the insects are most to be dreaded) at first obtain some relief by covering their faces and hands, but they soon feel it difficult to endure the heat, are weary of being condemned to complete inactivity, and finish with leaving the face and hands uncovered. Persons who would renounce all kind of occupation during the navigation of these rivers, might bring some particular garment from Europe in the form of a bag, under which they could remain covered, opening it only every half-hour. This bag should be distended by whalebone hoops, for a close mask and gloves would be perfectly insupportable. Sleeping on the ground, on skins, or in hammocks, we could not make use of mosquito-curtains (toldos) while on the Orinoco. The toldo is useful only where it forms a tent so well closed around the bed that there is not the smallest opening by which a gnat can pass. This is difficult to accomplish; and often when you succeed (for instance, in going up the Rio Magdalena, where you travel with some degree of convenience), you are forced, in order to avoid being suffocated by the heat, to come out from beneath your toldo, and walk about in the open air. A feeble wind, smoke, and powerful smells, scarcely afford any relief in places where the insects are very numerous and very voracious. It is erroneously affirmed that these little animals fly from the peculiar smell emitted by the crocodile. We were fear fully stung at Bataillez, in the road from Carthagena to Honda, while we were dissecting a crocodile eleven feet long, the smell of which infested all the surrounding atmosphere. The Indians much commend the fumes of burnt cow-dung. When the wind is very strong, and accompanied by rain, the mosquitos disappear for some time: they sting most cruelly at the approach of a storm, particularly when the electric explosions are not followed by heavy showers.

Anything waved about the head and the hands contributes to chase away the insects. "The more you stir yourself, the less you will be stung," say the missionaries. The zancudo makes a buzzing before it settles; but, when it has assumed confidence, when it has once begun to fix its sucker, and distend itself, you may touch its wings without its being frightened. It remains the whole time with its two hind legs raised; and, if left to suck to satiety, no swelling takes place, and no pain is left behind. We often repeated this experiment on ourselves in the valley of the Rio Magdalena. It may be asked whether the insect deposits the stimulating liquid only at the moment of its flight, when it is driven away, or whether it draws the liquid up again when left to suck undisturbed. I incline to this latter opinion; for on quietly presenting the back of my hand to the Culex cyanopterus, I observed that the pain, though violent in the beginning, diminishes in proportion as the insect continues to suck, and ceases altogether when it voluntarily flies away. I also wounded my skin with a pin, and rubbed the pricks with bruised mosquitos, and no swelling ensued. The irritating liquid, in which chemists have not yet recognized any acid properties, is contained, as in the ant and other hymenopterous insects, in particular glands; and is probably too much diluted, and consequently too much weakened, if the skin be rubbed with the whole of the bruised insect.

I have thrown together at the close of this chapter all we learned during the course of our travels on phenomena which naturalists have hitherto singularly neglected, though they exercise a great influence on the welfare of the inhabitants, the salubrity of the climate, and the establishment of new colonies on the rivers of equinoctial America. I might justly have incurred the charge of having treated this subject too much in detail, were it not connected with general physiological views. Our imagination is struck only by what is great; but the lover of natural philosophy should reflect equally on little things. We have just seen that winged insects, collected in society, and concealing in their sucker a liquid that irritates the skin, are capable of rendering vast countries almost uninhabitable. Other insects equally small, the termites (comejen),* (* Literally, the eaters or the devourers.) create obstacles to the progress of civilization, in several hot and temperate parts of the equinoctial zone, that are difficult to be surmounted. They devour paper, pasteboard, and parchment with frightful rapidity, utterly destroying records and libraries. Whole provinces of Spanish America do not possess one written document that dates a hundred years back. What improvement can the civilization of nations acquire if nothing link the present with the past; if the depositories of human knowledge must be repeatedly renewed; if the records of genius and reason cannot be transmitted to posterity?

In proportion as you ascend the table-land of the Andes these evils disappear. Man breathes a fresh and pure air. Insects no more disturb the labours of the day or the slumbers of the night. Documents can be collected in archives without our having to complain of the voracity of the termites. Mosquitos are no longer feared at a height of two hundred toises; and the termites, still very frequent at three hundred toises of elevation,* (* There are some at Popayan (height 910 toises; mean temperature 18.7 degrees), but they are species that gnaw wood only.) become very rare at Mexico, Santa Fe de Bogota, and Quito. In these great capitals, situated on the back of the Cordilleras, we find libraries and archives, augmented from day to day by the enlightened zeal of the inhabitants. These circumstances, combined with others, insure a moral preponderance to the Alpine region over the lower regions of the torrid zone. If we admit, agreeably to the ancient traditions collected in both the old and new worlds, that at the time of the catastrophe which preceded the renewal of our species, man descended from the mountains into the plains, we may admit, with still greater confidence, that these mountains, the cradle of so many various nations, will for ever remain the centre of human civilization in the torrid zone. From these fertile and temperate table-lands, from these islets scattered in the aerial ocean, knowledge and the blessings of social institutions will be spread over those vast forests extending along the foot of the Andes, now inhabited only by savage tribes whom the very wealth of nature has retained in indolence and barbarism.