Ants under the conditions of an extremely hot summer

Abstract

Specific features of ant behavior during the extremely hot summer of 2010 were studied, as well as the aftereffects of this season on simple and complex family units of ants in 2011–2012. Simultaneous studies were carried out in southern taiga (Moscow Province, Verkhnaya Klyazma myrmecological protected area) and northern taiga (Arkhangelsk Province, Pinezhskii Nature Reserve). Ants of the genus Formica responded to the extreme heat by (1) changing their foraging patterns; (2) redesigning their nests; (3) rearranging the spatial and functional structure of the colonies. They switched to a bimodal activity pattern with maxima in the morning and in the evening and a prolonged daytime intermission. Along ant roads, there were underground pavilions with dense roofs built of conifer needles and soil. Covers of the same kind appeared over root aphid colonies. The most radical improvement was the construction of a battery of brood chambers underneath the mound. The soil excavated was used for strengthening the mound and restricting the convective heat exchange between the brood chambers and the external environment. The anthill surface was covered with a smooth crusted layer of soil and fine plant debris particles, which protected the nest from the inflow of hot air from without. A portion of the inhabitants of large nests moved to newly built extensions and auxiliary nests. It was only active, non-damaged colonies that could afford these measures and thus survive the heat with minimal loss. Depressed colonies lost the major part of their brood during this time. Furthermore, small secondary colonies that emerged as the result of destructive activity of animals also failed to reassemble due to the summer heat of 2010. The months of heat were followed by a long rainy and cool period, and the colonies that had already been depressed faced critical conditions for preparing for winter. The ants were unable to accumulate lipid reserves sufficient for spring nest heating and rearing of sexuals and workers, which turned out to be an important aftereffect of the 2010 season the following year. Two first generations of workers were absent in almost all the nests. Mass oviposition in F. aquilonia commenced only late in May 2011, whereas the flight of alates did not occur at all because alates of this species are only reared in spring. Consequently, the F. aquilonia colonies had not recovered even by the end of 2012. In F. lugubris and F. polyctena, species that rear sexuals twice a year, there was only late-season alate flight, and yet it allowed their colonies to replenish the pool of ovipositing females and restore the initial colony size by the end of 2012. Other ants, represented by Lasius niger and Myrmica rubra, also modified their nests and foraging patterns during the period of heat. M. rubra suffered the most, so that its abundance and activity remained very low in 2011 as well. Only L. niger, which remained practically unscathed by the heat, successfully completed its annual cycle in 2010. Therefore, one of the 2010 year’s results was a drastic shift in the ratio of nests built by the abovementioned species in favor of L. niger.