The big, little invasion: How non-native species eat into urban resources

Bengaluru: The impact of invasive biological species on urban spaces has been studied largely in their ecological context. There is consensus on the many risks non-native species bring to cities but the economic fallout of their presence is not deeply understood.

An international team of 19 researchers studied available data to assess the damage. The study prompts a re-look at the scale of the damage, finding that between 1965 and 2021, 61 invasive species accounted for cumulative costs of $326.7 billion across 24 countries (India not among them), at an average annual cost of $5.7 billion.

Costs in urban areas that constitute only between 0.6 per cent and 3 per cent of the earth's surface represent approximately 15 per cent of the total global economic impact caused by these species.

Invasive species are transported by humans beyond their natural bio-geographic range and can spread in their introduced range. Insects were found responsible for more than 99 per cent of the reported costs ($324.4 billion), followed by birds ($1.4 billion). The costs were largely reported in the public and social welfare sectors ($254.3 billion).

The US, China, and Australia reported the highest expenses — $261.5 billion, $518 million, and $169 million, respectively.

Under-reporting of costs

Ecologist and evolutionary biologist Alok Bang who was part of the team highlighted the poor understanding in countries, including India, of the social and economic impact of invasive species on urban areas. The study proposes stronger policies and greater stakeholder engagement to address the issue.

Titled Economic costs of invasive non-native species in urban areas: An underexplored financial drain and published in Science of the Total Environment, the study cited predictions that the number of most taxonomic groups of invasive species will increase until 2050.

It also revealed under-reporting of costs in other countries — 73 countries have occurrences of costly invasive species in urban areas but no monetary costs were reported. The statistics were sourced from InvaCost, a global database of economic costs attributed to invasive species.

The expenses were grouped under damage costs, management costs, and a mixed category. Invasive species have been found to impact the quality of people’s lives, including through damage to buildings and public infrastructure. “They also feed on stored food, cause allergies, and transmit diseases. These impacts become particularly significant in densely populated areas where a larger number of people are affected more quickly,” Bang, a researcher at the Azim Premji University in Bhopal, told DH.

Topping the list of the “costliest” species is the Formosan subterranean termite at $252.1 billion which is 77.2 per cent of the total costs. The emerald ash borer ($3.7 billion), the red fire ant ($1.6 billion), the Mediterranean fruit fly ($1.6 billion), and the feral pigeon ($1.4 billion) make the top 5. Costs caused by other species, like the Aedes mosquitoes, are likely to have been underestimated, Bang said.

A paper Bang co-authored in 2022 estimated that between 1960 and 2020, invasive species cost India between $127.3 billion and $182.6 billion but most of these costs were not assigned to specific sectors, types, or contributing species.

Two non-native plants accounted for 95 per cent of the total costs recorded for invasive plants — the common ragweed which affects the health sector (damage losses), and the halfa grass which increases the management costs.