Formica is a palaearctic ant genus to which monogyneous and polygyneous societies of various species belong. They build mound-nests variable in size and structure in which the brood grows in chambers located in different parts of the nest. According to Dzierzon`s rule, males develop from unfertilized and females from fertilized eggs. The sexuals will grow in the upper part of the nest at spring time and the workers, also from fertilized eggs, in the lower part in the summer. As eusocial insects, the female castes, queens and workers, are permanent inhabitants of the nest showing a division of labour. Males are grown often in early spring together with the queens. As adults both sexual forms can leave the nest for mating. In the summer, unfertilized eggs are also present, but the developing larvae die in the 2nd stage. Sexuals and workers develop from different types of eggs. The larger eggs, needed for producing sexuals, are laid in the spring and the smaller ones, from which workers result there after. Besides the egg type young workers soon after hibernation, loaded with stored lipoproteines, are needed for growing sexuals, and are frequently present in highly populated societies. In the early spring these workers are found in a temperature regulated area in the mound of the nest together with the egg-laying queens. The workers serve as nurses of the developing larvae and of the queens.

For caste determinatioin, besides these biotic conditions various ecological requirements are necessary. In the early spring there is no food input from the outside, and the secretory head glands of the workers produce the food given to the larvae by trophallaxis. The postpharyngeal glands serve as lipoprotein producers, while the labial glands have a reservoir filled with a surger solution. The crop stores mainly the food coming from the outside.

The different types of eggs develop in the ovaries at different seasons. To develope the larger oöcytes containing a pole plasm with high RNA content, the queen has to be vernalized and hibernate at a low temperature. Only then sexual forms will develope. In F. polyctena (Foerster) the smaller summer eggs (s-eggs) do not develop sexuals, in spite of a large food supply. The oosomes of the winter eggs (w-eggs) contain a large amount of RNA, than the s-eggs, but this difference does not translate in a quantitative effect, since the RNA concentration is not higher in w-eggs than in s-eggs. Both egg types do not differ in their RNA components, except in the nucleotide fraction which is higher throughout the embryogenesis of the s-eggs. In both egg types, the pattern of fluorescent compounds is different, and the presence of riboflavine-pteridine compounds is necessary for growing sexuals until determination occurs at the end of the first larval stage. Male larvae also have to be determined to become adults.