According to a major recent report by the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES), more than 37,000 alien species have been introduced globally via various human activities. Of these, more than 3,500 are invasive alien species that pose major global threats to nature, the economy, food security and human health. Invasive alien species have played a key role in 60 percent of global plant and animal extinctions and costed the global economy more than $400 billion a year—a figure that has quadrupled every decade since 1970. With the increased movement of people and goods driven by globalization, environmental degradation and climate change, the number of invasive alien species and their impacts are projected to increase. In response to this critical issue, the 15th Conference of the Parties to the Convention on Biological Diversity (COP15) adopted an international target of reducing the introduction and establishment of invasive alien species by at least 50 percent by 2030. Furthermore, at the G7 Ministers’ Meeting on Climate, Energy and Environment held in 2023, the members agreed to create and share a database of information on invasive alien species, strengthen research on monitoring and early detection, and establish a system to prevent the spread of invasive alien species, with private sector involvement.

Ants are among the most devastating invasive alien species. Their broad diets, nesting habits and high reproductive capacity allow them to reach extremely high population densities in their introduced range, where they often outcompete native species and disrupt biodiversity. They can also present a danger to agriculture and pose serious public health risks. Indeed, the total economic damage to the agriculture and public welfare sectors caused by invasive alien ants that has been reported in 27 countries since 1930, is estimated at $51.93 billion. As a result, nineteen ant species are recorded in the Global Invasive Species Database (IUCN), five of which are listed among the “100 of the World’s Worst Invasive Alien Species”: the Argentine ant (Linepithema humile), red imported fire ant (Solenopsis invicta), African big-headed ant (Pheidole megacephala), little fire ant (Wasmannia auropunctata) and yellow crazy ant (Anoplolepis gracilipes). Furthermore, the small size of ants facilitates their transport by human activities and their establishment and spread. Consequently, over 200 ant species have established populations outside their native ranges, of which approximately 20 additional species have been identified as potentially invasive or highly invasive.

The management of invasive ants is a highly diverse, complex task and includes preventing entry, monitoring high-risk areas, removing new invaders and addressing existing incursions. Consequently, to improve management decisions on invasive ants, it is necessary to share the knowledge gained from past management efforts. Furthermore, the global movement of goods and people unintentionally facilitates the spread of invasive ant species. To effectively prevent their spread, we must work together and share information and resources to address this issue through collaborative efforts and comprehensive strategies. In this special issue of Global Environmental Research, experts report the latest research on controlling invasive alien ants in various countries and regions, including the United States, mainland China, Hong Kong, Taiwan, South Korea and Japan. I laud these experts for providing valuable knowledge and expertise on the challenges of preventing and managing invasive alien ant threats and hope that this special issue will facilitate global efforts to establish effective management strategies for invasive alien ants.

Guest Editor

Yoshiaki HASHIMOTO

Institute of Natural and Environmental Sciences, University of Hyogo / The Museum of Nature and Human Activities Hyogo

The red imported fire ant, Solenopsis invicta Buren, is one of the most serious invasive alien species, and has destructive effects on native biodiversity, agriculture and public health. In Japan, the S. invicta invasion was first discovered on May 26, 2017, in a shipping container transported from China. Since then, the threat of S. invicta establishment in Japan has been increasing due to its ongoing arrival via cargo container traffic from China. Here we describe the imminent threat of S. invicta establishment in Japan. Furthermore, in Japan, nesting of S. invicta has been continually discovered in cracks in the asphalt pavement of container yards, and winged queens have been detected in those nests. This further increases the threat of its establishment. We discuss why its nesting occurs in container yards and the risks of container yards as a bridgehead for S. invicta establishment. To date, Japanese border control measures have successfully eradicated the ants by detecting their invasion in its early stages. However, further infestation via containerized cargo, and nesting in container yards, increase the likelihood of S. invicta establishment before first detection. Therefore, we have developed novel, effective techniques to prevent S. invicta from entering containerized cargo and from nesting in container yards. These new techniques are introduced in this article, along with further management recommendations.

The red imported fire ant (RIFA; Solenopsis invicta), native to South America, is one of the most notorious invasive alien species, known for causing various extensive economic damage in the regions they invade. After invading the United States in the 1930s, RIFA began expanding into Asian countries in the early 2000s, establishing populations in China and several other countries. Recently, further dispersal has been observed from these newly invaded regions into Japan and South Korea, where the first RIFA invasions were reported in 2017. The primary RIFA invasion route into these countries has been through maritime logistics using sea containers. Therefore, to prevent future invasions and establishment of RIFA, the most critical measure for pre-invasion control is the development of “clean” maritime logistics systems that minimize the risk of RIFA transportation. We have been developing a RIFA repellent transportation technology utilizing allyl isothiocyanate (AITC), a natural insect-repellent compound derived from wasabi (Eutrema japonicum). To control the high volatility of AITC, we chose to utilize microencapsulated AITC (mAITC), which encapsulates AITC within resin microcapsules. After verifying the repellent and fumigant effects of mAITC against RIFA in small-scale experiments, we conducted trials using actual sea containers. These experiments demonstrated that mAITC effectively prevents the invasion of RIFA into cargo. The implementation of mAITC in maritime transportation is expected to play a crucial role in preventing the global invasion of RIFA while simultaneously reducing the risk of invasive alien species being introduced through maritime logistics.

Among invasive species, alien ants show particularly high levels of ecological impacts. One such species, the Argentine ant Linepithema humile, has invaded and established populations worldwide, causing significant damage to biodiversity and human society. Although chemical control measures against invading populations of Argentine ants have been implemented in various countries, successful eradication cases remain rare. In Japan, this species is listed as a Designated Invasive Alien Species under the Invasive Alien Species Act, placing the responsibility for its control on local governments. Our research team at the National Institute for Environmental Studies, has developed effective control methods for the invading Argentine ant populations based on population-ecology and pesticide-science approaches. As a result, we have successfully eradicated nearly all Argentine ant populations in the Kanto region of Japan.

The browsing ant Lepisiota frauenfeldi native to southern Europe has been introduced through human activities to broad areas globally since 2017. In areas it has invaded, the ant is known to rapidly increase its population and particularly to prey on native ant species. We conducted ant monitoring surveys once a month using a time-unit sampling method on two routes, Route A and Route B, at Nanko Port, Osaka, Japan between 2021 and 2023. On Route A, the browsing ant was observed with the highest frequency, accounting for 77 to 100 percent of the population throughout the survey period, and eight other ant species were observed. The number of Le. frauenfeldi individuals decreased from September 2021 to January 2022, peaked in June 2022, and hit a low in January 2023. On Route B, this ant was not observed at any time during the survey period, but ten other ant species were observed. The diversity and evenness of ants at the site that had been invaded were much lower than at the site not invaded, suggesting that the presence of Le. frauenfeldi had a negative effect on diversity and even distribution of local ants. In addition, we investigated the distribution of Le. frauenfeldi using the time-unit sampling method over the wider area of Nanko Port (375 ha), dividing it into 15 grids. Our results showed the browsing ant to be found only in grids in the southeastern part of Nanko Port. These results suggest that the species currently has a limited range in this area, highlighting the importance of early control measures before its distribution expands.

White-footed ants of the genus Technomyrmex (Hymenoptera: Formicidae) originated from Asia but have invaded several subtropical regions of the globe and have become significant pests in recent years. Invasive populations of T. brunneus in Japan have ecological characteristics typical of other invasive ants, such as polygyny, unicoloniality, pre-adaptation to disturbed habitats, and herbivorous but flexible feeding habits. This species shows extreme polygyny and high reproductivity, because its colonies include numerous intercastes (worker-like queens). Therefore, population densities reach high levels, leading them to become a serious nuisance as household pests. Additionally, T. brunneus possesses other characteristics that make its control difficult, such as arboreality, absence of trophallaxis, low insecticide susceptibility, and bait preference biased to liquids. Recent studies have revealed that hydrogel baits, which are liquid baits sustained by superabsorbent polymers, are suitable for controlling this species. Here we review the pest status, ecology, and control of T. brunneus and indicate future research directions to stop the damage it causes.

It has been 20 years since the red imported fire ants (RIFA) was first detected in Taiwan. Currently, this ant has appeared across most of northern Taiwan, including the remote islands of Kinmen and Lienchiang. Right after the invasion, the National Red Imported Fire Ant Control Center (NRIFACC) was established. Technologies for alien ant management have also burgeoned among governmental institutes and private sectors. In our study, liquid nitrogen freezing, hot water vapor steaming and dry ice treatment showed a more than 80 percent control rate against individual RIFA nests. Unmanned aerial vehicles (UAV) for broadcasting pesticide were tested for increased safety of pest control specialists. Detection dogs were able to locate RIFAs and their nests in nursery farms, construction sites, airports and seaport terminals with an indication rate of over 90 percent. When conducting a large area-wide survey using bait traps, the Fire ant Automatic Image Recognition System (FAIRS) could be used to distinguish RIFA from other ant species with a true positive rate of about 90 percent, while showing RIFAs’ location on a map, reducing the labor cost. Finally, a mobile game regarding ant farming and RIFA management were developed to raise people’s awareness of the impact of invasive ants on the environment and ecosystems, and draw attention to the concepts of biosecurity and richness of biodiversity. Some of the technologies mentioned above were also listed in the Standard Operating Procedures for Fire Ant Control issued by Taiwan’s government.

The little fire ant, Wasmannia auropunctata, is an invasive tramp ant that causes damage on a global scale. Recently, this notorious ant species was first reported in Taiwan in 2021. This is considered the first confirmed case in the East Asian region. Colonies of W. auropunctata were found at two locations, i.e., Wuri and Heping districts in central Taiwan, which are separated by approximately 30 km. Both genetic and behavioral analyses revealed that the two populations were most likely introduced from a common source population, and form a unicolonial social structure. Furthermore, a microsatellite analysis showed that W. auropunctata populations in Taiwan also employ clonal reproduction. Because of its highly aggressive nature, we highlight the potential threats this invasive ant species poses to arthropod communities, agricultural systems and human health in this region, based on several field observations. A food lure method using potato chips was adopted to detect the presence of W. auropunctata. Since September 2021, the monitoring and chemical control of W. auropunctata populations have been addressed through a university-government partership. The eradication program included both ground and arboreal treatments. Ground treatments involved mixing granular baits containing pyriproxyfen (0.50w/w%) with granular baits containing hydramethylnon (0.73w/w%) at a ratio of 4:1, and then broadcasting the mixture onto the ground at an application rate of 2.5 kg/ha. Arboreal treatments involved spraying paste baits containing borax (2w/w%) at an application rate of 10 L/ha over tree trunks and vegetation.

The red imported fire ant, Solenopsis invicta Buren 1972, is one of the most damaging invasive ant species, causing ecological, economical and social impacts in many regions worldwide. Since its first record in mainland China in 2004, it has rapidly spread across multiple provinces, including Hong Kong and Macau, driven by the country’s extensive transportation system and favorable climatic conditions. This review provides an overview of the distribution and ecological impacts of S. invicta in mainland China, focusing on its interaction with native species, disruption of ecosystem processes and implications for human societies. Additionally, the S. invicta invasion has led to significant agricultural damage, increased infrastructure costs, higher public health risks such as allergic reactions, and socio-economic disruptions. Finally, this review offers policy recommendations for timely detection, public awareness and international cooperation to mitigate the ongoing and potential impacts of S. invicta.

Invasive alien ants pose significant economic and ecological threats in the United States, with the red imported fire ant (Solenopsis invicta), the Argentine ant (Linepithema humile) and the Asian needle ant (Brachyponera chinensis) exemplifying the challenges. This review examines the status, distribution and management strategies of these species, with a particular focus on recent research advances in control methods. Innovations such as water-resistant baits, RNA interference, viruses, integration of trail pheromones, hydrogels, prey-baiting and trapping box strategies enhance the specificity and efficacy of invasive ant control while addressing the unique behaviors of target species. We propose that a comprehensive approach, integrating both traditional and novel species-specific strategies, is essential for advancing invasive ant management and adapting to the growing diversity of invasive ants arriving and establishing in the United States.

The alien species invasion continues to proceed, fueled by human-mediated international trade and climate change, leading to significant reductions in biodiversity and posing threats to public health. The global economic impacts are also substantial, with estimates suggesting costs of approximately US$1.288 trillion over the past 50 years. Among these, insect invasions have become increasingly frequent each year, resulting in significant economic, health and ecological damage. This study reviews the strategies currently implemented at the national level in South Korea for managing invasive alien ant species and proposes future improvements. By presenting an overview of current management practices and their efficacy, this study aims to contribute to the development of more effective and sustainable management strategies for invasive alien ant species in South Korea.