Short Communication |
Corresponding author: Diego López-Collar ( dlopezcollar@gmail.com ) Academic editor: Francisco Hita Garcia
© 2021 Diego López-Collar, Francisco J. Cabrero-Sañudo.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
López-Collar D, Cabrero-Sañudo FJ (2021) Update on the invasion status of the Argentine ant, Linepithema humile (Mayr, 1868), in Madrid, a large city in the interior of the Iberian Peninsula. Journal of Hymenoptera Research 85: 161-177. https://doi.org/10.3897/jhr.85.65725
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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.
Formicidae, green areas, introduced species, invasive species, new records, Spain, urban environment
The Argentine ant, Linepithema humile (Mayr, 1868), is a well-known and widely studied organism due to its highly potential as an invasive species (
In the Iberian Peninsula, L. humile has a predominant coastal distribution (
In this way, green areas, parks, and botanical and private gardens located in urban environments provide microhabitat scale conditions, in terms of humidity, food and shelter resources, which not only allow but also favour the development of Argentine ant colonies (
The present article compiles all the records of the Argentine ant, L. humile, obtained from various samplings across the city of Madrid and its surrounding areas between 2018 and 2020, including previous information from the bibliography, citizen science web platforms and personal communications. The aim of this study was to update the available information on the Argentine ant in the city of Madrid and nearby locations.
Records of the Argentine ant, L. humile, were searched and catalogued from different sources, involving mostly green areas in the city of Madrid and its surroundings. These references were obtained from: (i) the bibliography (B, Table
Localities where samplings have been carried out and/or the Argentine ant has been registered. Classification of localities (city of Madrid and surroundings): B, the species has been registered according to bibliographic references (
Sampling areas | Location | Classification | Presence/Colony extension | Date of sampling | Pitfall traps | Time spent (min) | Nº of visits |
---|---|---|---|---|---|---|---|
City of Madrid: green areas | |||||||
Casa de Campo Park (east side) | 40°25.020'N, 3°44.040'W | B | ✓ | 2011 | – | – | – |
S | ✓/ 11816 m2 | 2018–2019 | Yes | 184 | 3 | ||
Madrid Río Park (Central part) | 40°25.133'N, 3°43.340'W | P | ✓ | Prior to 2019 | – | – | – |
S | ✓ / 54494 m2 | 2019–2020 | Not practicable | 122 | 2 | ||
Real Jardín Botánico de Madrid | 40°24.660'N, 3°41.460'W | BV | ✓ | 2016 | – | – | – |
S | ✓ / 2857 m2 | 2018–2019 | Not practicable | 91 | 2 | ||
del Norte–CarmenTagle Park | 40°28.843'N, 3°41.734'W | S | ✓ / 377 m2 | 2018 | Yes | 121 | 3 |
Enrique Tierno Galván Park | 40°23.312'N, 3°40.961'W | S | ✓ / 1974 m2 | 2018 | Yes | 143 | 3 |
Sorolla Museum Gardens | 40°26.120'N, 3°41.540'W | S | ✓ / 830 m2 | 2020 | Not practicable | 25 | 2 |
Campus Moncloa, North side | 40°26.930'N, 3°43.688'W | S | No presence | 2010–2019 | Yes | Continuous monitoring | 3+ |
Bellas Artes Gardens | 40°26.410'N, 3°41.425'W | S | No presence | 2018 | Yes | 25 | 3 |
Campo del Moro Gardens | 40°25.068'N, 3°43.089'W | S | No presence | 2018 | Yes | 119 | 3 |
Berlín Park | 40°27.026'N, 3°40.547'W | S | No presence | 2019 | No | 76 | 2 |
Cuña Verde de la Latina Park | 40°24.048'N, 3°44.620'W | S | No presence | 2018 | Yes | 158 | 3 |
Pradolongo Park | 40°22.545'N, 3°42.384'W | S | No presence | 2019 | No | 156 | 2 |
Roma Park | 40°24.988'N, 3°39.762'W | S | No presence | 2018 | Yes | 101 | 3 |
Emperatriz María de Austria Park | 40°22.741'N, 3°43.422'W | S | No presence | 2018 | Yes | 156 | 3 |
Entrevías Urban Park | 40°22.224'N, 3°40.107'W | S | No presence | 2018 | Yes | 104 | 3 |
Eugenia de Montijo Park (part 2) | 40°23.032'N, 3°45.014'W | S | No presence | 2018 | Yes | 69 | 3 |
Forestal de Valdebebas Park | 40°29.466'N, 3°37.994'W | S | No presence | 2019 | No | 184 | 2 |
Forestal de Vicálvaro Park | 40°24.476'N, 3°35.894'W | S | No presence | 2018–2019 | Yes | 135 | 3 |
Juan Carlos I Park | 40°27.642'N, 3°36.324'W | S | No presence | 2018 | Yes | 184 | 3 |
Quinta de Torre Arias | 40°26.688'N, 3°37.190'W | S | No presence | 2018 | Yes | 115 | 3 |
City of Madrid: Streets | |||||||
Campus Moncloa, east side, Rector Royo–Villanova Street | 40°27.120'N, 3°42.960'W | B | ✓ / Unknown | 1991–1992 | – | – | – |
P | Unknown | 2019 | Not practicable | – | – | ||
Valmojado Street, Aluche Neighbourhood | 40°23.220'N, 3°45.540'W | P | ✓ / Unknown | 24/01/2004 | Not practicable | – | – |
Alfonso XII Street, Jerónimos Neighbourhood | 40°24.660'N, 3°41.333'W | S | ✓ / 2440 m2 | 2018–2019 | Not practicable | 25 | 2 |
Príncipe de Vergara Street | 40°25.382'N, 3°40.826'W | S | ✓ / 225 m2 | 2020 | Not practicable | 25 | 2 |
Nueva España Neighbourhood (various streets) |
40°27.560'N, 3°40.358'W | BV | ✓ | 2011 | – | – | – |
S | ✓ / 93290 m2 | 2019–2020 | Not practicable | 157 | 3 | ||
Outside the city of Madrid | |||||||
Aranjuez | 40°2.220'N, 3°36.300'W | B | ✓ | 1952–1968 | – | – | – |
P | ✓ / Unknown | 2019 | – | – | |||
Pozuelo de Alarcón | 40°27.50'N, 3°48.28'W | B | ✓ | 1952–1968 | – | – | – |
Pozuelo de Alarcón, Vereda de las Columnas Street, El Paular Neighbourhood | 40°27.50'N, 3°48.28'W | P | ✓ / Unknown | 2020 | Not practicable | – | – |
Rivas–Vaciamadrid | 40°21.540'N, 3°32.820'W | B | ✓ | 2011 | – | – | – |
P | ✓ / Unknown | 2010 | – | – | – | ||
Villanueva de la Cañada, Villagolf residential area | 40°26.700'N, 3°59.880'W | P | ✓ / Unknown | 2019 | Not practicable | – | – |
The survey data correspond to a series of samplings in green areas of the city carried out from 2018 to 2020, between May and September of each year. Three locations do not correspond to green areas but to streets, where the same sampling protocol was applied (S, Streets, Table
Variables used in the park selection process sorted by type, with a brief description.
Type | Variable | Description |
---|---|---|
Geographical | Latitude and longitude | Georeferences of the park centroid |
Spatial | Area and perimeter | Surface spatial attributes |
Orientation | Ratio between longitude and latitude differences. | |
Shape | Ratio between perimeter and area. It gives an idea of the edge effect. | |
Management | Timetable | Opening hours |
Type of management | ‘Naturalised’ or ‘garden’ type of management | |
Urban matrix | Distance between parks | Distance between park centroids |
Distance to city centre | Distance from park centroids to centre of the city (centroid of all parks) | |
Distance to wildlife sources | Corresponding to large naturalised areas*. | |
Surrounding green areas | Surface of other green areas in buffers of 100 m, 250 m, 500 m, 1000 m, 1500 m, 2000 m, 2500 m and 5000 m |
Ants were directly sampled with an aspirator, and pitfall traps were used to maximise the sampling effort whenever they could be set due to impracticable ground conditions or when permits could not be obtained (
Those sites where L. humile was found were properly surveyed to measure the surface area covered by each colony. To assess the expansion limits of the colony, workers of Argentine ant were searched and mapped until they were no longer seen after having walked through the area in concentric circles, moving 50 to 100 metres away from the ant trails. The extent of the colony reflected in QGIS software (
The presence of the Argentine ant was recorded in a total of eleven points within the urban area of the city of Madrid and four peripheral locations (Fig.
The bibliographic search resulted in three documents that located the presence of the Argentine ant in five locations (B, Table
Nine of the 23 localities exhaustively sampled in the city of Madrid during the last three years showed the presence of L. humile (39.1% of the locations sampled; S, Table
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.
Enrique Tierno Galván Park is located in the south of the city (40°23.312'N, 3°40.961'W). With a size of 41 hectares, it is considered a large park. An Argentine ant colony was found, with its foraging tracks extending over almost 2000 square metres, where the water supply remained constant (with irrigation systems covering the grass meadows). The colony had access to plants with aphids and elements where the species could take shelter and walk easily, such as cobblestones and road gutters (Fig.
Colony extension and foraging areas of the Argentine ant in nine locations of Madrid. A Enrique Tierno Galván Park B del Norte-Carmen Tagle Park C Real Jardín Botánico de Madrid and Alfonso XII Street D Príncipe de Vergara Street E Sorolla Museum Gardens F Nueva España Neighbourhood G Casa de Campo Park (east side) and Madrid Río Park.
Del Norte-Carmen Tagle Park is located in the north of the city of Madrid (40°28.843'N, 3°41.734'W), extending over 20 hectares. The colony foraging area covered approximately 380 square metres, including areas of irrigated meadows and cobblestones with ornamental shrub vegetation (Fig.
In the Real Jardín Botánico de Madrid (Royal Botanical Garden; 40°24.660'N, 3°41.460'W), the presence of the Argentine ant confirmed a previous record (
Argentine ant workers photographed in the city of Madrid. Both photographs belong to the citizen science platform ‘Biodiversidad Virtual’. A Real Jardín Botánico of Madrid, by José Fernández (
A colony was also detected on Alfonso XII Street (40°24.660'N, 3°41.333'W), adjacent to the Real Jardín Botánico de Madrid. The workers may have come from inside the Jardín Botánico itself, which would act as a focal point, since several entrance trails to the possible nest were identified on a wall on the even-numbered side of the street, where a line of ants extended over approximately 300 metres (Fig.
Approximately 830 square metres are occupied by the Argentine ant in the garden in front of the Sorolla museum (Fig.
A highly widespread Argentine ant population was found along the streets and gardens of Nueva España neighbourhood, in Chamartín District, with an approximate area of 9.3 hectares (40°27.560'N, 3°40.358'W; Fig.
Another location where the Argentine ant is relatively abundant corresponds to a section of the Madrid Río Park, mainly between El Puente del Rey and El Puente de Segovia (two bridges over the Manzanares river), including the Virgen del Puerto Gardens, although the presence of the ant extends beyond these points (40°25.133'N, 3°43.340'W). Linepithema humile presence was noticed by members of “Tecnormigas”, a group of ant fans from Madrid (M. Sierra pers. comm.) and verified on the ground, where numerous areas occupied by ants were detected along a wide extension on both sides of the Manzanares river (Fig.
This ant species is cited in the bibliography on a residential area at the eastern end of Ciudad Universitaria, northwest of the city (
Outside the urban district of Madrid, individuals of L. humile were found in private gardens in the residential area of Villagolf, 25 kilometres west of the capital (40°26.700'N, 3°59.880'W; Fig.
This article compiles for the first time new and previously known records of the Argentine ant in the city of Madrid and its surroundings. It shows a worrying situation that has not been previously considered and must be urgently addressed. The fact that L. humile has reached localities in the interior of the Iberian Peninsula, moving away from a coastal range, is unusual for a natural expansion (
Thus, we propose two ways in which the expansion can occur within the city itself: (i) directly, since reproduction takes place by budding (
The locations where the Argentine ant has been found in Madrid have a number of common characteristics that could allow it to survive and expand. Artificially irrigated areas offer an almost constant supply of moisture, which, combined with food resources that can be found in parks, gardens and even indoors, makes these areas highly valuable sites for nesting and foraging. Parks that are heavily disturbed (mowed and irrigated with sprinklers) are more likely to harbour exotic species like L. humile (
The location of Nueva España Neighbourhood (Fig.
In Enrique Tierno Galván Park, Del Norte Park and Real Jardín Botánico, the colonies are relatively small in extension, but their surroundings are potentially colonisable, given the structure and elements of these green areas. In addition, it should be considered that the city of Madrid has more than 200 green areas integrated into the urban matrix that may be considered attractive for this species, with a variety of suitable places for the Argentine ant to establish, depending on the park size, the level of irrigation, the refuges, etc. In these circumstances, the invasion of this species is taking place slowly but surely.
Therefore, given the strong likelihood that the Argentine ant will continue colonising the city of Madrid and the rest of the surrounding locations and given the negative effects that its presence may have on the diversity of other ant species (
Various methods have been used to control the Argentine ant, generally in natural environments and agricultural systems, mainly based on insecticides and toxic baits (
Certainly, the best strategy that can be carried out, as mentioned by several researchers (
The presence of the Argentine ant in Madrid and its surroundings reveals a gradual entry and a silent expansion within the city in recent years. Since it is likely that there will be new entries or movements of this species in the form of nest relocations, applying a monitoring system that involves citizens, researchers and local authorities should be really advantageous. These actions would prevent the city from becoming a ‘reservoir’ for the species, reducing the long-term chances of new enclaves being colonized by the Argentine ant, such as naturalized environments near the city.
We are grateful to the citizen science platform ‘Biodiversidad Virtual’ (especially to José Fernández and Álvaro Izuzquiza) for the georeferenced data and the photos of the Argentine ant. We also thank Javi Arcos (UAB), Kiko Gómez, Lola Martínez (UCM), Daniel Padilla (GSB), Joaquín Reyes (UCO), Mariano Sierra (Tecnormigas), Nuria Trotta (INTI, SA), Mª Ángeles Vázquez (UCM) and Josefina Cabrero for sharing information on the records referred to in this work. We are also thankful to the Community of Madrid and the Madrid City Council for the permits granted for the development of this project. We are very grateful to Xavier Espadaler for his comments and to an anonymous referee that helped us to substantially improve our manuscript.