Terrestrial cave-fauna are likely affected by the high concentrations of CO 2 frequently found in many cave habitats, typically over 10,000 ppm. Furthermore, air composition (radon, CO 2) characterizing the whole vadose zone and seasonal changes observed in cave-atmospheres are obvious ecological constraints for troglofauna. Cova de sa Font is a rather simple descending anchihaline cave (25 m deep), that stands out for its extreme CO 2 fluctuations throughout the year: from less than 800 ppm in the winter to values exceeding 60,000 ppm in the summer. This small cavern is actively ventilated during the cold season, but when ventilation ceases in the spring, it starts to be invaded by CO 2-enriched "ground air" coming from the surrounding vadose crevices. In order to assess the effects of rising carbon dioxide content on the terrestrial fauna of Cova de sa Font, a threefold sampling of troglobitic and troglophilic fauna was carried out, using baited pitfall traps, from December 2018 to October 2019. We describe the most noteworthy changes in the spatial distribution of several species and we indicate a strong correlation with confined-air descriptors. Our results suggest that these arthropods have adaptive abilities to live in such a CO 2-rich environment.