Sun Basking in Red Wood Ants Formica polyctena (Hymenoptera, Formicidae): Individual Behaviour and Temperature-Dependent Respiration Rates

Abstract

In early spring, red wood ants Formica polyctena are often observed clustering on the nest surface in large numbers basking in the sun. It has been hypothesized that sun-basking behaviour may contribute to nest heating because of both heat carriage into the nest by sun-basking workers, and catabolic heat production from the mobilization of the workers’ lipid reserves. We investigated sun-basking behaviour in laboratory colonies of F. polyctena exposed to an artificial heat source. Observations on identified individuals revealed that not all ants bask in the sun. Sun-basking and non-sun-basking workers did not differ in body size nor in respiration rates. The number of sun-basking ants and the number of their visits to the hot spot depended on the temperature of both the air and the hot spot. To investigate whether sun basking leads to a physiological activation linked with increased lipolysis, we measured respiration rates of individual workers as a function of temperature, and compared respiration rates of sun-basking workers before and two days after they were allowed to expose themselves to a heat source over 10 days, at self-determined intervals. As expected for ectothermic animals, respiration rates increased with increasing temperatures in the range 5 to 35°C. However, the respiration rates of sun-basking workers measured two days after a long-term exposure to the heat source were similar to those before sun basking, providing no evidence for a sustained increase of the basal metabolic rates after prolonged sun basking. Based on our measurements, we argue that self-heating of the nest mound in early spring has therefore to rely on alternative heat sources, and speculate that physical transport of heat in the ant bodies may have a significant effect.

Effect of mound size on intranest thermoregulation in the red wood antsFormicarufa and F. polyctena (Hymenoptera, Formicidae)

“…Over a 12 h period, the temperature in the nest can increase from +7-10 °C to + 20-25 °C, which favors the development of brood and oviposition, as demonstrated by our data and model. These data are also confirmed by more recent studies of lipolysis in the bodies of ants located on the surface of nests and in passive workers (Kadochova et al, 2017). Our present results also confirmed the findings of Zakharov (1972) that there is a certain critical size of the nest under which internal heating is insufficient for autonomous thermoregulation.…”

Ant nest architecture is shaped by local adaptation and plastic response to temperature

“…Owing to the landscape-scale climatic differences across a species’ range, nests built in different localities may differ markedly in form. Although there is evidence of a correlation between soil surface temperature and ambient temperature, respiration, and metabolic rates, further study is needed to determine why soil surface temperature influences nest-building behaviors in F. podzolica 34 – 36 . However, one possibility is that nest depth is a response based on the colony’s thermoregulatory needs.…”

Adaptations to thermal stress in social insects: recent advances and future directions

“…In wood ants ( Formica spp. ), workers leave the nest to bask in the sun; when they re‐enter the nest, the heat stored in their bodies is released (Kadochová, Frouz, & Roces, 2017; Kadochová, Frouz, & Tószögyová, 2019).…”