

PERIODS OF APPEARANCE ATH) DISAPPEARANCE. 277 



ft species of small gnats, called tempraneros* because they 

 appear also at sunrise, take the place of the mosquito* 

 Their presence scarcely lasts an hour and a half ; they die. 

 appear between six and seven in the evening, or, as they 

 say here, after the Angelus (a la oracion). After a few mi- 

 nutes' repose, you feel yourself stung by zancudos, another 

 species of gnat with very long legs. The zancudo, the pro- 

 boscis 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 zaucudos 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 alter- 

 nately 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,* where everything proceeds with such ad- 

 mirable regularity, we might ojuess blindfold the hour of the 

 day or night, by the hum of the insects, and by their stings, 



* 'Which appear at an early hour* (temprano). Some persons say, 

 that the xancudo is the same as the tempranero, which returns at night, 

 after hiding itself for som ctime. I have doubts of this identity of the 

 species ; the pain caused by the sting of the two insects appeared to me 

 different. 



f By the extreme regularity of the horary variations of the atmospheric 

 preMure. 



