Forest-built nest mounds of red wood ant Formica aquilonia are no good in clear fells

- Red wood ant Formica aquilonia nest mound surface layer was drier in clear fells.
- Moisture decreased with increasing relative nest height in clear fells.
- Temperature difference (inside-ambient) was affected by surface layer moisture.
- Moist nest mound surface layer may have an important role in the thermoregulation.

Temperature and humidity conditions affect the growth and success of ectotherm insects. Red wood ants of the Formica rufa group are able to regulate the temperature of their nests to be close to the optimum, typically higher than ambient in northern latitudes and higher elevation. The mound-shaped nests are constructed from organic particles (needles, sticks, etc., plant material) and from soil particles. Nest mounds typically have a relatively dry inner structure but moister surface layer which may help the ants to insulate nests against cooling winds. Forest clear felling exposes nest mounds to direct sunlight, drier microclimate and increased wind. We studied whether clear felling affects the nest surface moisture and temperature conditions. We found that i) nest surfaces were significantly drier in clear fells than in forests, ii) a high height/diameter ratio and an increase in the nest volume increases surface dryness in clear fells but not in forests, iii) the nest temperatures relative to ambient temperature was higher in forests than in clear fells, and iv) the relative temperature increased with increasing moisture content of nest surface layer. The drying nest material and more unstable inside temperature may have adverse effects not only on the red wood ants themselves, but also for nest-dwelling soil organisms and myrmecophiles that live in red wood ant nests. In addition, changes in moisture and temperature could have effects on the rate of decomposition and nutrient turnover.