[en] The species of ants and Ground beetles at Olkiluoto in Eurajoki were studied in the summer of 2008 during two trapping periods: in June and August. The research goal was to clarify the species on Olkiluoto island of the earlier mentioned groups, at least at the family level, and to collect samples for further examination by Posiva. The trapping areas were selected at Olkiluoto in Posiva test monitoring sectors, a part of the trapping areas was the same as the earlier study. Species of ants, depending on their particular species, are a very dominating group of insects. The ants are the most important predators, scavengers and soil movers in Finnish forests. It looks as if the biomass of ants may be more than 10% of the biomass of all animals in certain areas of Finnish forests. In Finland there are about 60 species of ants that have been observed. They have been divided into four sub-groups, which are Myrmicinae, Formicinae, Ponerinae and Dolichoderinae. In Finland there are close to 300 species of ground beetles (Carabidae), which are divided into dozens of different families. The species, to a great extent, consist mostly of predatory insects that prey on microbes in field layers, but a part of them are specialized in feeding on flora. Ground beetles are usually divided into three groups according to their choice of habitat: Species that favour open biotopes, species that favour forests, and generalist species that can thrive in a variety of environments. Ground beetles also reflect changes in their living environment, and possibly they can be significant as socalled bio-indicators. Pitfall traps were used as the method of research. The preservative fluid used was ethanol (50%) with dishwashing liquid to remove surface tension. The points were located in various different biotopes in fields, meadows and forests. The data collected was defined as a minimum for the family level of Ground beetles and for ants to the species or species pairs. The species of Ground beetles and ants found in the pitfall trap study represented a quite usual range of species for southern Finland and no rare or endangered species were detected amongst the individuals defined to their particular species. The number of individual ants appeared to be higher in biotopes that were predominantly forested with conifers but as far as the amount of species was concerned, the dispersion between different biotopes was great. The amounts of species and individuals concerning the ground beetles were higher in open field-and meadow habitats. The differences in sizes amongst the ground beetles are remarkable. The weight of a large individual Carabus hortensis is the same as the weight of several individuals of smaller species together. These species, together with Pterostichus niger and Patrobus atrorufus, make up the majority of the communities of ground beetles in Olkiluoto, both in numbers and in weight. (orig.)