Formica nigricans Emery, 1909 - an ecomorph of Formica pratensis Retzius, 1783 (Hymenoptera, Formicidae)

Workers and queens from 224 nest samples of Formica pratensis Retzius originating from all over Europe, but mainly from Germany were investigated for several morphological characters, particularly pilosity. Statistic differences between the hairy N morph (= F. nigricans Emery 1909) and the less hairy P morph in body size, pilosity, geographic frequency, habitat selection and mound construction could be shown but other aspects of external biology coincide. There are no suggestions of reproductive isolation of the morphs which are interpreted as different genotypes of the same population and represent different ecological adaptions. The strong decrease of N morph frequency in pratensis populations from S to N Europe, its higher frequency in more xerothermous habitats in Germany, and its well-documented peculiarity of constructing higher mounds than the P morph for conditions of equal sunexposure characterize the N morph as a genotype adapted to higher temperatures. In Germany, as much as 16% of pratensis nests investigated contained both morphs. Polycalic colonies are found in both morphs but isolated nests predominate. Formica minor pratensoides Gößwald 1951 is a synonym of pratensis and refers to polycalic colonies of the P morph which occasionally occur inside more mesophilic, less sun-exposed forests.