It Were To Be Wished That A Learned Entomologist Could Study On The Spot The Specific Differences Of These Noxious Insects,* Which In The Torrid Zone, In Spite Of Their Minute Size, Act An Important Point In The Economy Of Nature.

(* The mosquito bovo or tenbiguai; the melero, which always settles upon the eyes; the tempranero, or putchiki; the jejen;

The gnat rivau, the great zancudo, or matchaki; the cafafi, etc.) What appeared to us very remarkable, and is a fact known to all the missionaries, is, that the different species do not associate together, and that at different hours of the day you are stung by distinct species. Every time that the scene changes, and, to use the simple expression of the missionaries, other insects mount guard, you have a few minutes, often a quarter of an hour, of repose. The insects that disappear have not their places instantly supplied by their successors. From half-past-six in the morning till five in the afternoon, the air is filled with mosquitos; which have not, as some travellers have stated, the form of our gnats,* (* Culex pipiens. This difference between mosquito (little fly, simulium) and zancudo (gnat, culex) exists in all the Spanish colonies. The word zancudo signifies long legs, qui tiene las zancas largas. The mosquitos of the Orinoco are the moustiques; the zancudos are the maringouins of French travellers.) but that of a small fly. They are simuliums of the family Nemocera of the system of Latreille. Their sting is as painful as that of the genus Stomox. It leaves a little reddish brown spot, which is extravased and coagulated blood, where their proboscis has pierced the skin. An hour before sunset a species of small gnats, called tempraneros,* because they appear also at sunrise, take the place of the mosquitos. (* Which appear at an early hour (temprano). Some persons say, that the zancudo is the same as the tempranero, which returns at night, after hiding itself for some time. I have doubts of this identity of the species; the pain caused by the sting of the two insects appeared to me different.) Their presence scarcely lasts an hour and a half; they disappear between six and seven in the evening, or, as they say here, after the Angelus (a la oracion). After a few minutes' repose, you feel yourself stung by zancudos, another species of gnat with very long legs. The zancudo, the proboscis of which contains a sharp-pointed sucker, causes the most acute pain, and a swelling that remains several weeks. Its hum resembles that of the European gnat, but is louder and more prolonged. The Indians pretend to distinguish the zancudos and the tempraneros by their song; the latter are real twilight insects, while the zancudos are most frequently nocturnal insects, and disappear toward sunrise.

In our way from Carthagena to Santa Fe de Bogota, we observed that between Mompox and Honda, in the valley of the Rio Magdalena, the zancudos darkened the air from eight in the evening till midnight; that towards midnight they diminished in number, and were hidden for three or four hours; and lastly that they returned in crowds, about four in the morning. What is the cause of these alternations of motion and rest? Are these animals fatigued by long flight? It is rare on the Orinoco to see real gnats by day; while at the Rio Magdalena we were stung night and day, except from noon till about two o'clock. The zancudos of the two rivers are no doubt of different species.

We have seen that the insects of the tropics everywhere follow a certain standard in the periods at which they alternately arrive and disappear. At fixed and invariable hours, in the same season, and the same latitude, the air is peopled with new inhabitants, and in a zone where the barometer becomes a clock,* (* By the extreme regularity of the horary variations of the atmospheric pressure.) where everything proceeds with such admirable regularity, we might guess blindfold the hour of the day or night, by the hum of the insects, and by their stings, the pain of which differs according to the nature of the poison that each species deposits in the wound.

At a period when the geography of animals and of plants had not yet been studied, the analogous species of different climates were often confounded. It was believed that the pines and ranunculuses, the stags, the rats, and the tipulary insects of the north of Europe, were to be found in Japan, on the ridge of the Andes, and at the Straits of Magellan. Justly celebrated naturalists have thought that the zancudo of the torrid zone was the gnat of our marshes, become more vigorous, more voracious, and more noxious, under the influence of a burning climate. This is a very erroneous opinion. I carefully examined and described upon the spot those zancudos, the stings of which are most tormenting. In the rivers Magdalena and Guayaquil alone there are five distinct species.

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.

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