Characteristics of thermal processes in ant nests built under stones (Hymenoptera: Formicidae)

Abstract

Ants prefer to nest under stones. This is due to temperature regimes favorable to the development of ant broods. In this paper, we investigated the influence of stone and ambient parameters on ant nests and created a model of thermal processes in ant nests under stones. The simulation results were compared with temperature measurements. Temperature was measured under 20 stones under different illumination conditions (sun, penumbra and shade) for 3 ant species (Myrmica rubra, Formica cinerea, Lasius niger) in Ukraine from April to August 2021. Stones were categorized as hot, warm and cold. Each stone was checked once a week for the number of workers and brood. Under two stones, temperature was measured using loggers. The number of workers under hot stones in spring increased three weeks earlier than under cold and warm ones. In May-June, the maximum number of workers was recorded under hot stones. In July, the number of ants was minimal under all categories of stones. Larvae appeared under hot stones two weeks earlier than under other categories of stones. In August, the number of pupae under cold and warm stones was greater than under hot ones. Number of larvae and pupae was positively influenced by the diameter of the stone, whereas stone height did not exert an important role. Ants preferred to inhabit nests under large flat stones, which are easily heated in spring and warm the soil under them. Another important characteristic was the location of the stones. The highest brood development was noted in nests under stones in open areas well lit by the sun in the daytime. In summer ants migrated from under hot stones, because soil under it dry and warmed. Stones and their position may be important factors in accelerating the development of brood in colonies of ant species that do not have active thermoregulation.