Nest founding by mixed kin groups in communally nesting orchid bees

Neotropical orchid bees are the only tribe within the corbiculate bees that does not exhibit obligate eusociality, making them an intriguing study group with regard to the evolution of social behaviour. However, finding nests is challenging, and nesting behaviour has been described only for a small fraction of the known species. Here, we present nests and kinship analyses for the aerially nesting species Euglossa cybelia in Pacific lowland Costa Rica, revealing a unique case of communal nest founding by multiple sister groups with no apparent social hierarchies. Within the studied nests all females were mated and the majority of foundresses contributed to the first generation offspring. We hypothesize that the elaborate nest architecture and effort associated with its construction have promoted co-founding and communal nesting in E. cybelia.