When the weather is cold and cloudy, many people dream of sunbathing on a warm, tropical beach. What about ants? Evidence suggests that at least some ants spend time basking in the sun.
See, for example, this video of harvester ants (Pogonomyrmex) sitting in the sun after a rain.
News From Rockcliff Farms blog has photographs of imported fire ants (Solenopsis invicta) sunbathing in large groups during a midwinter warm spell.
Some possible reasons for sunbathing/basking:
- Warm up or increase body temperature, particularly in poikilotherms (animals whose internal body temperature varies with the external environmental temperature)
- Exposure to ultraviolet light can kill microorganisms, such as bacteria, on the outer surface
- Exposure to ultraviolet light in vertebrates induces the production of Vitamin D
In his 1995 book Animal Architecture, Juhani Pallasmaa stated wood ants (Formica sp.) use heat captured by basking in the sun to warm their nests.
Kadochová, Frouz, and Roces (2017) recently tested this idea in the laboratory. They found Formica polyctena workers are willing to bask under an artificial heat source, which in this case was an infrared lamp. The authors of the paper didn't find evidence basking workers had a sustained increase in metabolic rate, but did suggest that heat energy absorbed during sun basking can be dissipated enough to increase the temperature inside of the nest. Cool! (yeah, I couldn't resist.)
The authors of the study found certain behavioral castes bask more than others. It would be worth investigating if workers which spend more time with the brood are more likely to bask. The ability to increase the nest temperatures around the brood during cold spells would likely be an advantage.
What do you think?
Kadochová Š, Frouz J, Roces F (2017) Sun Basking in Red Wood Ants Formica polyctena (Hymenoptera, Formicidae): Individual Behaviour and Temperature-Dependent Respiration Rates. PLoS ONE 12(1): e0170570. doi:10.1371/journal.pone.0170570
(Amazon Affiliate Link)
Pallasmaa, J. 1995. Animal architecture. Helsinki: Museum of Finnish Architecture. 126 p.