30 



In the same geographical position, however, the mosquito shows a 

 disposition to spread over continents rather than to invade the islands, in 

 accordance with Humboldt's observation that those insects are more abun- 

 dant along the shores of large rivers than upon the islets and that 

 mosquitoes are more troublesome close to the banks than in the centre of 

 rivers. To this circumstance may, perhaps, be due the silience of the first 

 chroniclers of the Discovery of America about mosquitoes, with reference 

 to the first voyages of Colombus. *) I have not found any mention of 

 them with reference to the Antilles before 1538, when Hernando de Soto's 

 soldiers having to cross a river near Puerto de los Principes, were so 

 severely bitten by mosquitoes that large marks of blood appeared on their 

 backs. To the comparative immunity of islands must probably be attri- 

 buted the following account given to Osten Sacken (quoted in Brehm, V. 

 IX, p. 446) by an American traveler. In 1823 mosquitoes were unknown 

 on the Hawaian Isles; but between 1828 and 1830 an old ship from Mexi- 

 co was abandoned close to the shores of one of those islands. The inhab- 

 itants soon noticed around that spot some blood-sucking insects previously 

 unknown to them; and the natives used to come in the evening to allow 

 themselves to be bitten by those extraordinary insects. Mosquitoes after- 

 wards multiplied and spread on those islands, developing into a regular 

 plague. 



Although mosquitoes are found in all latitudes, their abundance 

 varies in different localities. Humboldt and Bonpland, in their Travels 

 in Equinoctial America wrote: "The annoyance suffered from mosqui- 

 toes and "zancudos" in the torrid zone is not so general as most people 

 think. On the high plateaux more than 400 toises (2500 feet) above the 

 sea-level, and in very dry plains, far from ljarge rivers, such as Cumana 

 and Calabozo, gnats are not much more abundant than in the most popul- 

 ous parts of Europe". The influence of dryness and of a long distance 

 from water-courses, pointed out by those travelers, is easily understood, 

 inasmuch as the larvae and puppae of the mosquitoes are aquatic, and 

 the winged insect requires water for the laying and hatching of its eggs. 

 The impediment to their propagation at high levels may consist in the 

 exaggeration of the diffculty which those insects must always experience 

 in flying upwards after they have filled themselves with blood ; a difficulty 

 which will be much more marked in a species having such small wings as 

 those of the C. mosquito. The rarefaction of the atmosphere at those 

 great heights necessarily increases that difficulty, and, under those 

 circumstances, the mosquito will instinctively shun those localities. The 

 above mentioned travelers also relate that a missionary priest, Bernardo 

 Zea, had built himself a room over a scaffolding of palm boards, and they 



1) This is a mistake, for I have since found the abundance of mosquitoes on the 

 Island Hispaniola specially mentioned in Herrera (Década I, Lib. V, cap. XI, p. 179). 



