Rhythms and Nocturnal Activities of Wood Ants in the Neuwied Basin, Germany 2010-2016

In situ activity patterns of two Formica-rufa group species (F. pratensis; F. polyctena) were continuously studied at four different red wood-ant nests during six months in each of the years 2010, 2011, 2012, and 2016 and related to weather factors and variations of the Earth’s magnetic field. In situ activity patterns of both species are similarly periodic and exhibit ultradian, and short and long infradian rhythms under natural Light:Dark conditions. Crepuscular and nocturnal activities ≤ 4-hr long were observed in both species, especially at the new moon and first quarter after the astronomical twilight in a period of darkness in fall. We hypothesize that local variability in Earth’s magnetic field affects long-term activity patterns, whereas humidity and temperature were more strongly associated with ultradian rhythms (less than 20 hr).