Those who have not traveled the great rivers of tropical America, like the Orinoco or the Magdalena, cannot imagine how all day long, ceaselessly, you are tormented by mosquitoes that float in the air, and how this crowd of little animals can make huge stretches of land uninhabitable. However used to the pain you may become, without complaining; however much you try to observe the object you are studying, the mosquitoes, jejenes and zancudos will tear you away as they cover your head and hands, pricking you with their needle-like suckers through your clothes, and climbing into your nose and mouth, making you cough and sneeze whenever you try to talk. In the Orinoco missions the plaga de las moscas, or plague of mosquitoes, is an inexhaustible subject of conversation. When two people meet in the morning the first questions they ask each other are, 'Que le han parecido los zancudos de anoche? and 'Como estamos hoy de mosquitos? ('How were the zancudos last night? and 'How are we for mosquitoes today?').

While Bonpland worked day and night dividing our herbal collections, thousands of obstacles prevented our departure from Havana. No ship would take us to Porto Bello or Cartagena. People seemed to enjoy exaggerating the difficulties faced crossing the isthmus and the time it takes to go by ship from Guayaquil to Lima. They reproached me for not continuing to explore those vast rich Spanish American lands that for over fifty years had not been open to any foreign travelers. Finding no boat I had to hire a Catalonian sloop anchored at Batabanò to take me to Porto Bello or Cartagena, depending on how the Santa Marta gales might blow. The prosperity of Havana, and its mercantile links with pacific ports, allowed me to procure funds for several years. I was able to exchange my revenues in Prussia for a part of General Don Gonzalo O'Farrill's: who was Minister to the Spanish Court in Prussia. On the 6th of March the sloop I had hired was ready to sail.