1. Burrows are specific structures created by animals, characterised by specific conditions different from those in the surrounding environment. Therefore, burrows may play a role for many other animals than their owners. To test this view, we have chosen the burrows of red foxes Vulpes vulpes and badgers Meles meles, two main burrow dwellers from among medium-sized carnivores in Europe.

2. The main aim of the study was to show the importance of carnivore mammals' burrows for invertebrates. However, in contrast to previously published results concerning invertebrate burrow fauna, which were based mainly on analysis of nesting material, we used a new method based on pipe traps with optimised sampling time.

3. The investigated burrows were either visited only occasionally or abandoned. We chose typical, commonly accessible burrows from the environment, located in forest patches around the city of Poznań in western Poland.

4. During the research, we sampled 4440 invertebrate individuals. In total, we identified at least 91 species. The most numerous were mosquitoes, which, however, were represented only by one species, Culex pipiens. Among other groups, we recorded Coleoptera, Diptera, Arachnida, Heteroptera, Hymenoptera, and Lepidoptera. In total it confirms that burrows are important wintering place for many invertebrates.

5. The novelty of the study is underlining the fact that burrows created by medium-sized carnivores are commonly used as invertebrate overwintering shelters especially by mosquitoes. Number of mosquitoes varied between burrows in high range and is a significant predictor of the other species abundance.