<p>The tawny crazy ant (Nylanderia fulva) is an invasive species rapidly spreading across diverse habitats, particularly those influenced by human activities. In Costa Rica, its recent arrival has raised questions regarding its influence on pre-established ant communities. Therefore, we evaluated changes in an ant community after the invasion of the tawny crazy ant on the main campus of the University of Costa Rica, where it likely arrived in 2020. We compared post-invasion ant diversity in 2023 to pre-invasion data from Corrales-Moya and Hanson (Tecnociencia 19:133–141, 2017). Our findings reveal a notable decline in native species richness and an alteration in community composition, particularly in vegetated areas, suggesting that the invasion of the tawny crazy ant is changing local biodiversity patterns. These changes altered species dominance and reduced community similarity across sampled microhabitats. Furthermore, we identified genera that appears to have resisted the invasion, such as Solenopsis and Wasmannia, suggesting potential resistance mechanisms. Changes in ant communities and loss of species richness highlight the ecological threat posed by the tawny crazy ant. Continued invasion is expected to produce local extinctions, underscoring the need for management strategies.</p>