Around 1847, in colonial Calcutta, an unexpected visitor arrived, likely hidden in plant crates or trade goods from East Africa. The giant African snail (Lissachatina fulica) entered India without fanfare, admired at first for its size and shell. But what seemed ornamental soon revealed itself to be the country’s most persistent invasive alien species.

Thriving in the region’s warm, humid climate and free from natural predators, the snail spread rapidly with human help, from Bengal’s gardens to the farmlands of the Western Ghats. By the mid-20th century, crops and ornamental plants had been ravaged, native snails displaced, and soil ecosystems altered. Worse, the snail had become a carrier for parasites like the rat lungworm, threatening humans and wildlife.

The giant African Snail is an example of how slow-moving, unnoticed arrivals can reshape ecosystems. Poor quarantine, a lack of rigorous monitoring, and policy failures allowed this mollusc to get far and wide. A world of rising global trade and subsequent species movement increases the risk of similar invasions.

Trade and invasive alien species

The surge in global trade since the 1800s has indirectly contributed to biological invasions in both terrestrial and aquatic ecosystems. The number of alien species rose 20x by the early 19th century. Bilateral trade agreements increased from 76 countries forming 5,700 trade pairs in 1948 to 186 countries forming over 34,000 pairs by the early 2000s. Now, trade tariffs mooted by the Trump administration in the U.S. are contributing to changing, reviving or initiating new trade deals between countries.

Invasive alien species are introduced by increased human activity around the globe. The introduction of these exotic species can be deliberate or accidental. For example, the introduction of cane toads (Bufo marinus) in Australia, Gambusia in India and Poecilia reticulata in Japan are examples of deliberate biocontrol initiatives gone wrong. On the other hand, accidental introductions often happen via the export and import of biological goods, such as timber, plant products, vegetables, fruits, and grains.

Biofouling is one such introduction scenario. When ships travel between countries without cargo, they are filled with ballast water to help the ship stay stable on the high seas. Biofouling — the undesirable accumulation of plants, animals, and algae on surfaces — sometimes occurs during the filling and flushing of ballast water, transporting exotic species from one region to another. The Asian paddle crab was introduced from the Northwest Pacific and East Asian waters to New Zealand, where it carries the white-spot syndrome virus, in this way.

When trade takes a turn

Shifting trade agreements and new ties between previously unlinked nations may further the spread of novel invasive alien species between continents. Countries may focus on forming relationships rather than imposing stricter sanctions on imports from new trade alliances. Some nations may not have the infrastructure to support checks on imported or exported goods given the sudden rise in new trade partners. In such scenarios, India too is at risk of letting more invasive alien species enter our borders.

India has been a major exporter and importer of exotic species. Several species are in different stages of establishment and spread in the country, making it difficult to track their entry and expansion. Many are introduced in the ornamental pet trade, especially the aquarium trade, or for biocontrol purposes as in the cases of mosquitofish (Gambusia species), guppies (Poeciliareticulata), and angelfish (Pterophyllum scalare). Some species are introduced through the food industry, such as Tilapia, which was brought to boost food production but instead established itself in Indian waterways, eventually outcompeting native freshwater fish species.

In another example from 1955, when food was scarce in India, the government imported wheat from the U.S. under their PL 480 (‘Food for Peace’) programme. But the wheat was of an inferior quality and contaminated with Parthenium seeds, and first entered the Pune market. Today, Parthenium grass is widespread in India, being found even in the remote corners of the Andaman and Nicobar Islands.

A 2022 study found that India has lost $127.3 billion (Rs 830 crore) to invasive alien species over the last 60 years, rendering the country the second-most financially affected by invasive alien species in the world, after the U.S. But this data only stems from the calculated costs of 10 invasive alien species from the 2,000+ alien species known in India.

Indeed, negative economic impacts have been recorded for only about 3% of known invasive alien species in India; such data remain unavailable, underreported, or overlooked for the remainder. Semi-aquatic and aquatic invasive alien species pose a greater fiscal burden than terrestrial species because they often affect high-value sectors like public health, water infrastructure, and fisheries, where control and damage costs are significantly higher. Indeed, the highest monetary burden from semi-aquatic species is solely from the yellow fever mosquito, which is a financial liability as well as detrimental to public health.

One Biosecurity

To reduce the risk of importing invasive alien species, India needs to strengthen its national policy. Specifically, it means enforcing stricter biosecurity at ports and other entry points and developing real-time species-tracking and early-warning systems that can catch invasion events before they get out of control.

The country also needs greater collaboration between government departments and researchers to maximise knowledge generation about potentially invasive species and their spread given various climate change scenarios and shifting trade routes.

Finally, India must implement mandatory post-trade biological impact assessments, typically in quarantine facilities managed by the respective department, to ensure unwelcome guests are not here to stay.

Implementing and strengthening policies to reduce the spread of invasive species is one step towards managing their consequences on the native biodiversity. In the light of the prevailing international trade agreements, the risk of these species’ introduction remains high due to a lack of infrastructure, dedicated institutions, and policies focused on mitigating their spread. Freight transport between growing economies is projected to triple by 2050, especially maritime and air cargo transport, increasing invasion risk by reducing travel time and improving the survivability of alien species.

Today, we’re still experiencing the effects of alien species introduced several decades ago. Similarly the effects of alien species introduced in 2025 will only surface decades in future, when it may be too late to reverse the tide. Strengthening India’s border biosecurity must be a top priority to avoid the worse consequences of invasion. Like One Health, a ‘One Biosecurity’ framework if implemented at the earliest will better our chances of managing invasive alien species.

Priya Ranganathan is a doctoral student at the Ashoka Trust for Research in Ecology and the Environment (ATREE), Bengaluru, studying wetland ecology and ecosystem services. Nobinraja M. is a post-doctoral fellow at ATREE working on invasive alien fishes.