Hybridization in the European carpenter ants Camponotus herculeanus and C. ligniperda (Hymenoptera: Formicidae)

The first case of hybridization between the large European carpenter ants Camponotus herculeanus (Linnaeus 1758) and C. ligniperda (Latreille 1802) is demonstrated by means of exploratory and hypothesis-driven data analyses of standardized phenotypic characters. The strong signal separating the parental species allows the identification of hybrid workers on the individual level, based on only seven characters. The frequency of hybridization between the two species is estimated for Central Europe as 0.2-1.0%. This low ratio indicates strong reproductive barriers considering syntopic occurrence at about 10% of the observation sites, a nearly complete overlap of swarming times and basically equal meteorological conditions to release swarming. The presented case increases the known ratio of hybridizing species within the 178 ant species of Central Europe to 19.1%. This figure dramatically contrasts the known hybridization ratio of 0.55% within an estimated number of 2000 ant species from the Holarctic outside Central Europe. This 30-fold lower discovery rate of hybrids may be explained by the predominance of idiosyncratic species delimitation methods in morphology-based taxonomy in combination with the psychology of human decision-making. A neotype of Camponotus ligniperda is fixed in a specimen from the terra typica and comments on the Latin naming are given.