Resumen en español

We describe a dense nest aggregation of Ancyloscelis aff. apiformis, two nests of Centris flavifrons, and six nests of Euglossa. We found a nest of E. analis built inside a cavity of a living tree, an aerial nest of E. cybelia attached under a leaf of a palm tree and four nests of E. nigropilosa associated with timber buildings and abandoned nests of carpenter bees (Xylocopa sp.). We report for the first time wasps of the family Eurytomidae (Hymenoptera: Chalcidoidea) and a cuckoo bee, Coelioxys (Rhinocoelioxys) sp. (Hymenoptera: Megachilidae), attacking the brood cells of E. cybelia and E. nigropilosa. We also briefly discuss the variation found in the nest structure of C. flavifrons; unlike those nests studied in Costa Rica and northeastern Brazil, the nests in Colombia were shallow (~12 cm) and consisted of a main tunnel with three short branches, each one ending in a single cell. Further data from other localities are needed to detect other variations in the nesting biology and if they are correlated with the morphological variation exhibited by this species or with local differences in parasite pressure.