Red wood ants Formica polyctena switch off active thermoregulation of the nest in autumn

Abstract

To explore timing of nest thermoregulation and its consequence with ant activity, we performed a field study in 12 nests of Formica polyctena along an altitudinal gradient. We recorded inner nest temperature in different nest layers (5, 10 and 15 cm beneath the nest surface) using manual measurement and nest core temperature using continuous datalogger measurement. Potential heat sources, weather conditions and ant activity patterns were also examined. The temperature difference between the depths of 10 and 5 cm was on average positive, which indicates a thermal flow from inside the nest, highlighting the importance of inner heat sources. The highest inner nest temperature was reached in June and the lowest in September. Linear models revealed a significant difference in the thermoregulatory pattern between September and the rest of the year. From April to August, inner nest temperature was affected by weather (air temperature, precipitation, and solar radiation), nest properties (moisture, number of nest openings, nest identity) and ant activity (number of foragers entering the nest). In September the only significant factors were precipitation and nest properties (moisture, number of nest openings, nest identity). Thus, we can assume that in the period of ant activity (April–August) nest thermoregulation is actively maintained by ants, whereas later in autumn red wood ants switch to passive nest thermoregulation.