New geolocated records of the invasive ant Linepithema humile (Mayr, 1868) are added to the previous references for the city of Madrid and its surroundings, and the possible causes of the occurrence and permanence of this species in urban areas are discussed. The data collection corresponds to a series of samplings carried out for the last three years in green areas of the city, bibliographic searches, citizen science platforms and personal communications. To date, eleven locations in the urban area of Madrid and four points outside the city have been registered. The city of Madrid is undergoing a colonisation by the Argentine ant, although it is not widespread yet, since observations over time and space are isolated and apparently unrelated. However, this species has a great capacity to disperse and establish new colonies, mainly human-mediated through the transport of goods, plants, gardening tools, etc. Considering the numerous colonizable urban green areas in the city that can provide the necessary conditions for its expansion, the Argentine ant should not be underestimated, and immediate action is strongly recommended.

Los bioindicadores han demostrado ser herramientas muy útiles para la evaluación del estado de perturbación o madurez de los ecosistemas, así como en la monitorización y detección de cambios en el entorno. Teniendo en cuenta una serie de criterios que justifican la calidad de los grupos bioindicadores, diversos taxones de artrópodos podrían ser considerados como óptimos. Existen varios estudios que utilizan a los artrópodos como bioindicadores, especialmente en zonas urbanas. Se exponen algunas experiencias de monitorización llevadas a cabo en los últimos diez años por el Grupo de Seguimiento de Biodiversidad UCM en el Campus Moncloa, un área periurbana situada en el noroeste de la ciudad de Madrid, relacionadas con el seguimiento de poblaciones de artrópodos (mariposas, hormigas y libélulas). Por último, se resumen algunas recomendaciones y perspectivas de futuro para el uso de artrópodos como bioindicadores en áreas urbanas.

The dragonfly Trithemis kirbyi Sélys, 1891 recently colonized Western Europe from North Africa. Since its first record in the Iberian Peninsula in 2007, the species has been spreading northward and has become naturally established in the central and eastern Iberian Peninsula, the Balearic Islands and southern France. Despite its worldwide distribution, its rapid colonization of the western Mediterranean area occurred only very recently. We found that the dispersal and recent establishment of T. kirbyi in southwestern Europe strongly depends on increasing temperatures, particularly summer temperature peaks, which has allowed this species to disperse farther and more effectively than during years with average summer temperatures. The most important variable in the suitability models is the minimum temperature of the coldest month, which, in recent decades, has become less of a limiting factor for ectotherms. According to the models, suitable areas for the species are currently found throughout the eastern Mediterranean parts of Europe, and it is likely that it can naturally colonize these areas as it did in the Iberian Peninsula. Trithemis kirbyi is a model of how climate change and observed rising temperatures have turned previously inhospitable regions into suitable areas for exotic species, which may successfully colonize them naturally if they can reach these promising lands on their own. However, this study serves as a warning that such species can also colonize these new regions with a little help from unsuspecting ‘friends’, which are often responsible for the increasingly common presence of invasive, noxious taxa in Europe.