The Night Shift: Nest Closure and Guarding Behaviors in the Stingless Bee, Tetragonisca angustula

Social insects face threats to the colony during the day but also at nighttime. Multiple strategies have evolved across social insect species that protect the nest and each other at night. We asked what behaviors are employed by stingless bees, Tetragonisca angustula at night. We describe two layers of defense, nightly nest closing and night guarding at the entrance. After monitoring 10 naturally occurring colonies, we saw considerable variation in the likelihood of colonies leaving a nest open or closing them at night. Furthermore, more guards were at the entrances of open nests than closed nests. The mass of nightly guarding bees and tube closers was consistent with (even slightly exceeding) the mass of daytime guards, suggesting that these tasks are performed by especially large soldier bees. We found preliminary evidence supporting the hypothesis that the kairomone citral, released by obligate kleptoparasites, encourages nest closing behavior. Two nests that were consecutively open for a week, partially closed the night we applied alarm pheromone. These data are just a glimpse into some of the nightly defensive behaviors and what shapes nest closure behavior. We discuss how these data are an important first step and discuss hypotheses emerging from this study.