Bees provide vital pollination services in both wild and agricultural ecosystems. Despite mounting evidence that neonicotinoid pesticides impair growth of bee colonies at sub-lethal levels of exposure, the mechanisms driving these effects remain unclear. While the receptors targeted by neonicotinoids are widespread within the insect central nervous system, potentially impacting a variety of key behaviors, previous work has focused largely on neonicotinoids’ effects on individual bees foraging outside the nest (i.e. on learning and navigation). Here, we investigate the impacts of a common neonicotinoid pesticide (imidacloprid) on social behavior within the nests of bumblebee colonies (Bombus impatiens). Using an automated behavioral tracking system, we show that exposure to a single, field-realistic daily intake of imidacloprid has drastic effects on nest behavior in bumblebees: treated bees showed reduced rates of brood care and activity after treatment. Imidacloprid-treated bees also shifted occupancy patterns within the nest and had fewer social interactions with nestmates, altering the structure of the social network within colonies. Our results demonstrate that neonicotinoids impact a range of vital behaviors in bees and suggest a new avenue by which these pesticides may affect social behavior in bees, impair colony growth, and impact the health of bee populations.