Nests and habitats
Even though ants seem to be found everywhere, they are not randomly distributed. The more structured the habitat, the easier it is for ants to choose a nest and find food. The nest site must meet the microclimatic requirements of the species. Especially the warmth-demanding brood requires a careful choice of location and sometimes ingenious nest constructions and behaviour. Ants strive to establish a temperature and humidity gradient in the nest. Unlike bees and wasps, which raise their offspring in fixed combs, ants constantly carry their brood to the most favourable places in the nest.
Nest types and space requirements
Ants differ considerably in body size, colony size and territory. The space requirements of individual species differ accordingly. Thus
For example, a complete Temnothorax colony can make do in an acorn, while a forest ant colony consists of hundreds of connected branch nests and can occupy several hectares. The fine-tuning of the nest climate and species-specific requirements determine the type of nest. The nests are in the ground with or without a mound, in wood, under stones and bark, between a rock and wall crevices, in acorns or galls, to name the most important possibilities.
In the simplest case, ants dig their chambers in the ground (ground nests, Fig. 4c), where the temperature and humidity conditions vary depending on the depth. The material is deposited as loose “sputum”. The earthworks can be observed particularly well after rainfall: Damage to the nest has to be repaired and the damp earth is needed for expansion and further construction.
Where the warming of the shallow soil is not sufficient, the earth nest is combined with a “solar collector” (combined earth nests). Nests are therefore often found under stones, dead wood and the like. At the same time, these structures shield against moisture. Many ant species build a solar collector themselves in the form of an “anthill”. In contrast to the scattering dome nests of the forest ants, earth heaps are destroyed by heavy rain and winter. Only with increasing plant growth do such heaps become stable.
Wood nests are gnawed by ants into the wood that is already damaged. Ants gnaw into already damaged wood, or beetle larvae expand their feeding tunnels. Low-density species such as Campo- notus truncatus or Temnothorax spp. only need a dead branch on the tree or ground, galls, or similar structures. Nests of populous species, such as the horse ants (Campo- notus herculean), are located inside the tree trunk and extend into the ground.
The populous shiny black wood ant Last- us fuliginosus lays its nest in hollow tree trunks. It fills the hollow space with a maze-like cardboard nest up to 0.2 m³ in size. The cardboard is made of chewed wood and earth materials and is abundantly saturated with honeydew. A certain fungus grows on this substrate and its threads penetrate and strengthen the thin-walled structure. In the microscope, the whole nest appears covered with velvet.
Warmth and winter hardiness
Ants are animals that need warmth. The life-limiting factor is not the winter cold, from which they can protect themselves by penetrating into deeper soil layers or producing their own antifreeze. Much more important is the sum of the heat available in the summer half-year for brood rearing. Ants have several possibilities to solve this problem.
First of all, the choice of habitat is decisive. In intensively sunlit, open places such as dry grasslands, south-facing slopes and in sparse deciduous forests and in sparse deciduous forests, ants find their greatest diversity of species. Unsuitable are wet, shady sites such as beech forests with dense crowns.
Within their habitat, ants choose places with special microclimatic conditions to build their nests. Under stones, for example, the temperature is significantly higher when exposed to sunlight than in the soil next to it. A stone slab in the garden can be so desirable that even different species live under it. In the mountains, stones are the only way to reach the necessary heat sums. There, certain ants even nest in pure rock crevices and have to endure temperatures of -30 to +40°C. The behavior of ants is less extreme. The situation is less extreme when living in tree crocks. There, ants can escape the damp and cold ground but are exposed to the winter cold, whereas large colony ants nesting in hollow trunks can retreat to the ground below.