Evidence for Ventilation through Collective Respiratory Movements in Giant Honeybee (Apis dorsata) Nests

The Asian giant honeybees (Apis dorsata) build single-comb nests in the open, which makes this species particularly susceptible to environmental strains. Long-term infrared (IR) records documented cool nest regions (CNR) at the bee curtain (nCNR = 207, nnests > 20) distinguished by marked negative gradients (ΔTCNR/d < -3°C / 5 cm) at their margins. CNRs develop and recede within minutes, predominantly at higher ambient temperatures in the early afternoon. The differential size (ΔACNR) and temperature (ΔTCNR) values per time unit correlated mostly positively (RAT > 0) displaying the Venturi effect, which evidences funnel properties of CNRs. The air flows inwards through CNRs, which is verified by the negative spatial gradient ΔTCNR/d, by the positive grading of TCNR with Tamb and lastly by fanners which have directed their abdomens towards CNRs. Rare cases of RAT < 0 (< 3%) document closing processes (for ΔACNR/Δt < -0.4 cm2/s) but also suggest ventilation of the bee curtain (for ΔACNR/Δt > +0.4 cm2/s) displaying "inhalation" and "exhalation" cycling. "Inhalation" could be boosted by bees at the inner curtain layers, which stretch their extremities against the comb enlarging the inner nest lumen and thus causing a pressure fall which drives ambient air inwards through CNR funnels. The relaxing of the formerly "activated" bees could then trigger the "exhalation" process, which brings the bee curtain, passively by gravity, close to the comb again. That way, warm, CO2-enriched nest-borne air is pressed outwards through the leaking mesh of the bee curtain. This ventilation hypothesis is supported by IR imaging and laser vibrometry depicting CNRs in at least four aspects as low-resistance convection funnels for maintaining thermoregulation and restoring fresh air in the nest.