## 1 Introduction  
Over the past century, urbanization has increased drastically in most regions around the world [1, 2, 3]. This increase threatens biodiversity [4, 5, 6], with pollution [7, 8, 9], habitat loss [10], and the spread of invasive species [11] being major causes of local species extinction or population decline. As such, urban habitats have historically been considered as species-poor concrete jungles [12]. However, urban environments are not necessarily depapureate ecosystems, and may, in fact, have some degree of conservation value by harboring native species [13]. Recent studies suggest that urban habitats can harbor a high diversity of both native (including endemic species) and non-native species, and even, sometimes, surpass surrounding rural areas in terms of species richness [12, 13, 14, 15, 16]. The survey and monitoring of biodiversity within cities may thus allow the identification of novel habitats and species worthy of protection within urban matrices. In particular, urban habitats including large and high quality patches of green spaces and forest fragments may still support high species diversity [17, 18, 19, 20]. How much biodiversity these areas can contain is still open for debate, but it is paramount to understand the potential conservation value of urban centers. Beyond assessing the number of species in cities, another crucial component to consider is the composition and identity of the species present. Indeed, cities can facilitate invasions by non-native species in part due to their high level of disturbance, which provides ecological niches suitable for many exotic species [21; 22; 23]. Moreover, the constant flux of merchandise in and out of urban centers through airports, harbors, and train stations make them the ideal gateways for exotic species introductions with the common arrival of new propagables [24; 25; 26]. Consequently, surveying urban centers and their surroundings to detect new arrivals is essential to limit their spread and mitigate their potential impact on native biodiversity. This is especially true for coastal regions, which host the highest richness of exotic species [27], and, in the case of China, may represent a source of spread towards more inland regions [28]. To evaluate the biodiversity value of urban environments, surveying all flora and fauna would be ideal, but unrealistic, especially for tropical and subtropical regions where there is limited data and taxonomic knowledge. As such, ecological surveys must select a subset of taxa representing useful biodiversity proxies. For conservation monitoring purposes, ants represent an ideal taxon [29]. Indeed, their taxonomy is relatively well-resolved in comparison with most other diverse insect groups, and they can be sampled through the use of standardized and replicable protocols [30]. They are also ecologically and taxonomically diverse, abundant, and ubiquitous [31]. Moreover, they are adequate bioindicators [32; 33], play key ecological roles as predators, scavengers, and herbivores [31; 32; 34; 35], with some species acting as ecosystem engineers by modifying soil properties [34]. Ants also include some of the most damaging invasive species, impacting native ants [36; 37; 35], non-ant invertebrates [38], vertebrates [39], and plant communities [40], ultimately causing ecosystem disruptions [41]. Invasive ant species can also negatively impact human socioeconomic activities such as farming or education [42], whereas others are considered household pests [43; 44], with some exotic species even acting as vectors of pathogens in hospitals [45; 46]. Thus, surveying the ant fauna of urban regions and producing ant species checklists should be an important tool not only to evaluate the conservation value of cities, but also to record the worldwide spread of exotic species. To date, the majority of studies have been limited to ecological studies (Table 1), limited in time and space, and using only a subset of sampling methods to characterize urban ant communities.