Locations of the Argentine ant in the city of Madrid. The letters in red circles correspond to locations where the Argentine ant has been recorded during the 2018–2020 surveys (areas in red). Letters in blue circles indicate bibliographic and personal communication records. The green areas correspond to parks and gardens that have been thoroughly sampled and where Linepithema humile has not been found, except for the eastern corner of the Casa de Campo Park (E). The light grey areas are green areas (parks and gardens) that have not been sampled and are capable of harbouring colonies of the Argentine ant.