The bionomics of sand flies (Diptera: Phlebotominae) was studied monthly for two consecutive years in alluvial gallery forests in the department of Casanare, Northeastern Colombia. A total of 2,365 specimens and 10 species were captured using CDC light traps and Shannon traps, and from diurnal resting places, and human landing collections. Lutzomyia fairtigi Martins (55%), Lutzomyia micropyga (Mangabeira) (20.9%), and Lutzomyia antunesi (Coutinho) (13.5%) were the predominant species in the region. Lutzomyia flaviscutellata and Lutzomyia panamensis, potential vectors of Leishmania in Colombia and neighboring countries, were also collected, but in low numbers. Lu. fairtigi is an endemic species to Colombia, and minimal data are available on its biology and distribution. The present study provides additional information about Lu. fairtigi, such as the diurnal activity displayed by females on cloudy days, the greater density during the rainy season (April to October), marked anthropophilia, and the presence of flagellates in the midgut of one female.