The plant genus Ficus (Moraceae) includes keystone tree species in tropical ecosystems, providing essential resources for a wide range of animals. Due to their ornamental value, fig trees have been introduced beyond their native ranges, often accompanied by their natural pollinators, which in some cases has led to ecological invasions. This study documents, for the first time, the presence of several pollinating and non-pollinating fig wasps (Chalcidoidea) on the Iberian Peninsula, focusing on three exotic Ficus species: Ficus microcarpa L.f., 1782, F. rubiginosa Desf. ex Vent., 1805 and F. macrophylla Pers., 1807. Through syconia sampling and dissection, we identified six fig wasp species: the pollinators Eupristina aff. verticillata (Waterston, 1921) and Pleistodontes imperialis Saunders, 1882, the gall-formers Eufroggattisca okinavensis Ishii, 1934, Josephiella microcarpae Beardsley & Rasplus, 2001, Walkerella microcarpae Bouček, 1993, and the parasitoid Philotrypesis okinavensis Ishii, 1934. Additionally, we documented several cases of non-native Ficus species reproducing spontaneously in urban areas, suggesting a significant ecological establishment and invasive spread through sexual reproduction. This spread poses potential risks to urban infrastructure, as the robust root systems of fig trees can damage buildings, pavements, urban trees, and heritage sites. Finally, we observed urban native and non-native bird species consuming mature fig syconia, which likely assist in the dispersal of these plants. Our findings underscore the need for further studies on the ecological impact of introduced Ficus species in non-native regions, their long-term economic consequences for urban heritage, and the continued monitoring of pollinator fig wasp populations.

Alien species, fig wasps, pollinator, parasitoid, Spain

Ficus L. is a well-known genus of woody plants commonly known as fig trees. The genus encompasses ca. 880 species mainly from tropical and subtropical regions (Harrison 2005; POWO 2023) and are considered ‘keystone species’ in many tropical ecosystems, as it provides shelter and trophic resources for a wide variety of animals (Shanahan et al. 2001; Herre et al. 2008; Compton et al. 2010). However, due to their ease of cultivation and appealing size, many Ficus species have also historically been used as ornamental trees and can now be found far from their regions of origin (Aumeeruddy-Thomas and Hossaert-McKey 2024). Fig. trees are characterized by their unique inflorescence, the fig, also known as syconium (Harrison 2005). For reproduction, fig trees rely on a complex and obligate relationship with fig wasps (Weiblen 2002) from the superfamily Chalcidoidea, which facilitate their pollination. For instance, the family Agaonidae, in its current circumscription, includes approximately 380 described, with an estimated 540 additional species yet to be described (Rasplus et al. 2025).

Agaonids are the main pollinators of Ficus species (Frodin 2004; Cardona et al. 2007; Rasplus and Soldati 2007). Female agaonids enter the fig through an aperture, the ostiole, which is closed by imbricated bracts. Once inside the receptacle, the wasps pollinate the flowers and lay their eggs in the ovules (Kjellberg et al. 2005). The larvae feed on the gall tissue induced during oviposition while the fig seeds and stamens mature. Wingless males emerge first, opening a small hole in the galled ovule containing females and mating with them while still closed in the gall. The males then dig a hole through the receptacle wall, allowing the females to emerge from the galled flowers. The females fill their pollen pockets with pollen (active pollination), or are dusted with pollen (passive pollination) and escape in search of a suitable fig tree (Kjellberg et al. 2005). Additionally, numerous Chalcidoidea wasps are gall-makers within Ficus ovules without fertilizing them, or act as parasitoids or inquilines of the pollinators or other non-pollinating fig wasps (van Noort 2003; Cook and Segar 2010; Cruaud et al. 2011a, 2011b; McLeish and van Noort 2012; Borges 2021). It is noteworthy that the mutualistic relationship between fig trees and their pollinators has traditionally been viewed as species-specific (Ramírez 1970; Weiblen 2002). However, several studies have shown that the one-to-one rule is often broken, with evidence of species complexes within several species (Rasplus 1996; Cook and Rasplus 2003; Molbo et al. 2003; Zhang et al. 2004; Haine et al. 2006; Jackson et al. 2008; Moe et al. 2011; Cornille et al. 2012; McLeish and van Noort 2012; Yang et al. 2012; Sutton et al. 2015). Additionally, when multiple agaonid species exist in a single fig species, they are usually sister taxa, or multiple pollinator species can develop within a single host fig species (Yu et al. 2019, 2021). While these studies mostly focused on pollinating fig wasps using molecular markers, very few works have questioned the genetic cohesiveness of fig species as they are currently understood (but see Haisne et al. 2006).

Due to this obligate mutualism, fig trees cannot produce viable seeds without their specific pollinators (Cook and Rasplus 2003; Herre et al. 2008; Speciale et al. 2015). Fig. trees are often planted outside their native range and have typically been propagated via cuttings. Subsequently, their pollinators have spread to areas where these trees have been planted as ornamentals (Caughlin et al. 2012). In some cases, fig species became invasive (Caughlin et al. 2012; Wang et al. 2015a) and spread into natural communities with consequences on local flora and fauna (Nadel et al. 1992; Hosking et al. 2011; Holmes et al. 2014; Riefner 2016; Demetriou et al. 2023). Beyond the impact on natural areas, the damage caused by introduced Ficus species in urban environments is important (Corlett 2006). These trees can make the ground slippery from fallen syconia and attract large numbers of insects (e.g., flies and wasps), leading to health issues and public nuisances (Wang et al. 2015a; Demetriou et al. 2023; Koutsoukos et al. 2025). Furthermore, fig trees develop strangler strong root systems and can grow in small cracks in buildings, walls and holes of other trees species, potentially widening them, causing significant structural damage in buildings (Wee 1992; Jim 1998; Jim 2010; Jim and Chen 2011; Morales-Gallegos et al. 2024; Koutsoukos et al. 2025), pavements (Esquivel and Quijas 2021; Demetriou et al. 2023), historical urban heritages (Caneva et al. 2009; Galanos 2015; Cozzolino et al. 2022; Metusala et al. 2023; Koutsoukos et al. 2025) or urban trees (Verloove and Reyes-Betancort 2011; Koutsoukos et al. 2025).

Therefore, it is particularly important to understand not only the actual distribution of fig wasps but also the potential impact of fig trees outside their natural range. In our study, our main goals are to a) record new species of pollinators and non-pollinator Chalcidoidea wasps for the Iberian Peninsula, b) document, for the first time, the spontaneous reproduction of exotic Ficus species in several areas of the Iberian Peninsula. Additionally, we discuss the potential impact of Ficus as invasive species and the damage they could cause to historical monuments in urban areas due to their robust root systems.

Biological invasions are of global concern with significant ecological, health, and socioeconomic impacts (Crystal-Ornelas and Lockwood 2020). New invasions are still being reported, especially by plants, underscoring the need for stronger prevention, monitoring, and eradication programs (Vantarová et al. 2023). One noteworthy case is that of Ficus species (Wang et al. 2015a). Although widely used for ornamental purposes worldwide due to their resistance and form (Goor 1965), it is only recently that certain Ficus species have begun to show invasive tendencies (e.g., Caughlin et al. 2012). The specific mutualistic relationship between fig trees and their pollinating wasps has typically restricted Ficus reproduction to asexual means outside their native range, limiting their spread and their potential as invasive species (Herre et al. 2008; Speciale et al. 2015). However, the reports of these wasps beyond their native habitats are increasingly common (see, for example, Koutsoukous et al. 2025 and references included), potentially enabling Ficus to cause invasions and have potential ecological and economic consequences (Caughlin et al. 2012; Rasplus et al. 2024; Koutsoukous et al. 2025). Many of these wasps may have been established in new regions for some time, yet due to their morphological and sometimes genetic similarities, their spread may have gone unnoticed due to misidentification or lack of detailed studies (Yu et al. 2019; 2021). Notably, this is the first report of some of these wasp species in the Iberian Peninsula, and the second of continental Europe (Koutsoukos et al. 2025), despite the prevalence of exotic plans in urban green spaces across Europe (e.g., DAISIE 2009; Čeplová et al. 2017). While pollinator wasps are the primary facilitators of invasions, other wasp species associated with Ficus also play significant roles. Non-pollinator wasps include gall-formers, seed predators, and parasitoids (Kong et al. 2016), which can negatively impact the reproductive success of fig trees by reducing both pollinator numbers and viable seed production (Kerdelhué and Rasplus 1996; Wang et al. 2015b). Thus, the potential role of these wasps as biological control agents cannot be ruled out, although their impact appears to be less significant than previously thought (Kong et al. 2016; Demetriou et al. 2023).

Our detection of sexual reproduction in Ficus species in Spain (and in mainland Europe), and outside their native ranges signals a new biological invasion case with potentially severe future impacts. Curiously, there are very few cases reporting the spontaneous sprouting of fig trees in Europe, most of them from island areas (e.g., Demetriou et al. 2023) or recently in continental areas (Koutsoukous et al. 2025). However, this problem could be greater than expected given the actual extent of cultivation of non-native Ficus in Europe. Urban trees, especially exotic species, have been shown to significantly damage infrastructure (Lee 2022), leading to costly repairs in the medium to long term. In several works, Ficus trees have already been identified as damaging pavements, urban infrastructure, sewage systems, historical sites, and local urban trees (e.g., Corlett 2006; Verloove and Reyes-Betancort 2011; Esquivel and Quijas 2021; Demetriou et al. 2023; Metusala et al. 2023; Morales-Gallegos et al. 2024; Koutsoukous et al. 2025). Thus, it is crucial to assess the impact of these newly observed Ficus seedlings and saplings on local infrastructure. Notably, many of these trees are already over 2–3 years old, indicating limited intervention on this issue by the administrators. As Ficus trees grow, their root systems expand, worsening cracks and causing progressively more difficult-to-repair damage (Morales-Gallegos et al. 2024). Additionally, these trees have a history of invading natural ecosystems, impacting ecosystem functions, and competing with native species, often spreading from urban areas (Nadel et al. 1992; Hosking et al. 2011; Holmes et al. 2014; Riefner 2016). Therefore, sexual reproduction in urban environments cannot be ignored as a future source of problems for seminatural and natural ecosystems (Wang et al. 2015a). The natural zoochorous (animal-assisted) dispersal of mature fig syconia by ants, birds and other vertebrates (Kaufmann et al. 1991; Starr et al. 2003) may further facilitate Ficus spread. We observed several cases of birds feeding on mature syconia, a behaviour previously documented in F. macrophylla and other Ficus species, like F. rubiginosa, by several non-native parrot birds in the Iberian Peninsula (Hernández-Brito et al. 2021). This reflects how the synergistic effect between fig wasp pollinators and potential dispersers (especially non-native ones) can promote the invasion of these plants and facilitate their spread from urban areas into the closest natural habitats.

With this new case of a biological invasion in the Iberian Peninsula, many questions remain. First, we need to refine our understanding of the distribution of these fig wasps and identify areas where they may promote the natural reproduction and spread of Ficus trees. Second, it is essential to assess the damage that Ficus can cause in urban and natural settings. Finally, it is important to investigate potential synergies with other species that may act as dispersers and amplify the invasive impact of these trees.