Invisible invaders: A new warning flag for molecularly detected alien species (MODAS) in databases and information systems.

Invasive alien species (IAS) threaten biodiversity, ecosystem functioning, and services. Early detection and monitoring are essential for preventing IAS spread and mitigating their impacts. Conventional monitoring approaches rely on physical evidence and frequently fail to detect species in inaccessible habitats, cryptic life stages, or poorly studied taxa. Advances in environmental DNA (eDNA) and other high-throughput molecular tools offer a sensitive alternative that can identify species undetectable by traditional methods. However, current regulatory frameworks require morphological verification, excluding molecularly detected IAS. Here, we propose adding molecularly detected alien species (MODAS) as a warning flag for alien species identified exclusively through molecular data. We define metadata requirements for the MODAS designation, including information on sampling, molecular analyses, DNA marker(s), sequence quality, taxonomic assignment confidence, and reference database. Incorporating MODAS flag into existing IAS databases and information systems would help prioritize validation efforts, support rapid response actions, and improve surveillance coverage, particularly in understudied or vulnerable environments. Moreover, tracking MODAS over spatial and temporal scales can provide critical feedback for refining and advancing IAS monitoring and surveillance approaches. This framework provides a precautionary, complementary approach for integrating molecular biodiversity tools into policy and management, promoting international coordination, and addressing gaps in current IAS monitoring strategies.