Millipedes under the Glass: Native and Non-Native Millipedes (Myriapoda: Diplopoda) in Greenhouses of Madrid (Spain), with Six New Records for the Iberian Peninsula

The millipede communities of heated greenhouses had never been studied in the Iberian Peninsula, despite their potential role as gateways for biological invasions. This study presents the first survey of millipede (Diplopoda) assemblages in Iberian greenhouses, providing a comprehensive list of species for the greenhouses of Madrid, Spain. We surveyed 14 greenhouses belonging to five institutions and identified 991 millipede individuals to species level. We documented 17 species, 8 of them native and 9 non-native; however, non-native species comprised 83.5% of specimens. Six species represent new records for the Iberian Peninsula, and one for continental Spain. Native species showed limited abundance and were restricted to less tropical greenhouse environments. We also report unexpected populations of two European and typically northern Iberian species, Nopoiulus kochii and Cylindroiulus punctatus in Madrid's greenhouses. Our findings confirm greenhouses as hotspots for non-native millipedes and highlight their role in species introductions. We recommend systematic monitoring of these artificial habitats.