Phenology and mortality of embryos in a Colombian population of Nymphargus grandisonae (Anura: Centrolenidae). Studies of phenology and natural history of anurans provide information useful for its conservation. This is particularly important in current scenarios of emergent diseases, high rates of deforestation, and climate change. We recorded the timing of breeding of the Glass Frog Nymphargus grandisonae and its relationship to precipitation and environmental temperature for four years in a population located in the Central Andes of Colombia, South America. In addition, we recorded the causes of mortality in egg clutches of this species. We quantified infestation by fly larvae and its impact on the survival of embryos. We found that the reproductive activity of N. grandisonae (number of males calling) was seasonal and occurred in months with highest precipitation. The main cause of embryo mortality in clutches was associated with the infestation by a spittlebug fly of the genus c.f. Cladochaeta (Drosophilidae). The survival of embryos in infested clutches was significantly lower than in those clutches not infested by fly larvae. Our results provide baseline data for the monitoring of anuran population dynamics in the Andean region using the glass frog N. grandisonae as a model system.