One of the key criteria used by the IUCN to assess species threat status is the extent of occurrence. Evaluating the true rarity of soil mesofauna, particularly mites, remains a major challenge in biodiversity research. In the suborder Uropodina, which includes numerous stenotopic species characterized by strong habitat selectivity, limited exploration of specific microhabitats may lead to underestimation of their actual distribution and abundance. As a result, species regarded as rare may represent habitat specialists occurring more frequently than current records suggest. The aim of this study was to analyze mite assemblages inhabiting nests of Lasius umbratus and to assess the significance of this microhabitat for species of the genus Oplitis, focusing on Oplitis franzi. The hypothesis that the apparent rarity of selected Uropodina species results from microhabitat specialization and association with a specific carrier was tested. Material was collected from nests of Lasius umbratus at three sites in western Poland (Bydgoszcz, Dabrówka, Krzesiny), representing an urban park, a semi-natural park, and a roadside tree site. Mites were extracted using Tullgren funnels and identified morphologically under an Olympus BX53 microscope with Nomarski contrast. Species composition and population structure within the studied microhabitats were analyzed. Numerous populations of Oplitis franzi were recorded at all sites. This species had previously been regarded as rare and was known only from isolated records in Spain, Poland, Slovakia, and Switzerland, with only females described in the literature. In the examined nests, individuals of both sexes and various developmental stages were found, indicating stable, reproducing populations associated with this microhabitat. Adult mites occurred both freely within the nest material and attached to the tibial spurs of Lasius umbratus workers, demonstrating a specialized dispersal strategy and close ecological association with the carrier. The findings indicate that the assumed rarity of this species resulted from incidental sampling outside its primary habitat and the lack of targeted studies focusing on this microhabitat. The analysis confirms that microhabitats such as ant nests (and other merocenoses) may represent important centers of biodiversity and play a key role in maintaining local invertebrate diversity. The study highlights the importance of precise microhabitat selection in mesofauna research for reliable assessments of species distribution, abundance, and conservation status.