By Salam Rajesh
Anyone following on the trail of invasive predators across the globe would be highly interested to know that ‘invasive’ species of animals, and plants, were mostly introduced intentionally to solve a problem, but ultimately becoming a problem by themselves.
So is this interesting story from the Australian continent where scientists made a huge mistake with introducing the predator species Cane toads (Rhinella marina) to resolve an issue with cane crops in Queensland, but finally finding themselves tied up with a Frankenstein species.
As the story goes, cane toads were introduced to Australia in 1935 to control sugarcane beetles, in particular the Greyback cane beetle (Dermolepida albohirtum). Cane toads are native to Central and South America.
The beetle larvae lived in the soil and chewed on sugarcane roots, stunting growth or killing the plants. Seeking a natural solution to kill the grubs, the Australian Government imported cane toads from Hawaii, with the hope that the toads would eat the grubs and save the sugarcane. That, as time revealed, was the fatal mistake.
By 1950, the Australian Government declared the cane toad as an invasive predator. Dangers from the toads included poisoning animals that prey on them, outcompeting native species for resources, and their voracious appetites.
Contradictory to the scientists’ theoretical hypothesis that the cane toads would gobble up all of the cane beetle grubs and resolve the issue, the toads totally ignored the beetles while decimating the very ecosystem they were meant to protect.
The toads became a highly toxic invasive species with no natural predators, and in fact, they became a huge threat to native amphibians, reptiles, and even small mammals and birds. That was the magnitude of the mistake the Australian scientists made in their ‘wise’ decision to bring in the predator cane toads.
Following the debacle, researchers found out that native tadpoles suffered mass mortality shortly after the toads were introduced to Queensland. Studies found that 1,300 tadpoles from 10 different species had died in one season alone.
It was also found that birds too suffered from the attack by the toads. For instance, the toads ate up the eggs and nestlings of the bird Rainbow bee-eater, resulting in a third of the bee-eaters’ nests to fail after the toads came in.
The end story is that despite decades of effort, large-scale control of cane toads in Australia remains nearly impossible to this day. The toads did not keep the beetle populations in check, rather, they had become one of Australia’s worst nightmare, and a most destructive invasive species and an ecological disaster.
Yet another story with a similar disaster in Australia happened with the common myna, native to Asia and a bird that is commonly seen in urban Imphal.
The common myna (Acridotheres tristis) was first introduced to Australia’s Melbourne between 1862 and 1872 to control agricultural pests. The bird’s distribution remained strictly localized for nearly a century and its population did not escalate until after the 1940s, when rapid post-war urbanization altered the eastern coastline into an ideal man-made habitat.
It was later found that the common mynas had become invasive in nature and were affecting agricultural crops. The IUCN reported damage by the invasive species to fruit crops, while other records indicated that the birds took advantage of food available in agricultural areas. They had also become competition for nesting hollows and threats to indigenous birds.
Quite interestingly, the International Union for Conservation of Nature (IUCN)’s Invasive Species Specialist Group includes the common myna in its ‘100 of the World’s Worst Invasive Alien Species’ list.
Then there is the story of Yellowstone National Park where the park authority in 2006 deliberately treated High Lake with the piscicide rotenone to remove introduced Yellowstone cutthroat trout that ‘misled’ scientists had intentionally stocked the predator fish in the lake decades earlier. The lake was originally in the range of the native Westslope cutthroat trout, now threatened by the introduced predator.
The rotenone is a naturally occurring botanical compound used as a piscicide to remove invasive, alien fish species from water bodies where the undesired fish species were introduced intentionally or accidentally.
The IUCN 20-year Strategic Vision identifies that responding to Invasive Alien Species is one of IUCN’s core existing conservation actions that needs scaling up. The vision document states that “over the next 20 years, IUCN will continue to use its world-leading data, knowledge and guidance to support policies, plans and their implementation to prevent the introduction and manage the impacts of invasive alien species” (Consultation for an IUCN Strategy on Invasive Alien Species, 2026).
Reflecting upon this global response strategy inked by the International Union for Conservation of Nature and Natural resources (IUCN), it is high time that the Manipur Government come up with strategies to combat the rising instances of invasive alien species of plants and animals in the State.
Based on the National Biodiversity Authority of India (NBA)’s listing of Invasive Alien Species (IAS) of plants and animals in the country, it is needless to say that Manipur has a well stocked population of the IAS including Water hyacinth (Pontederia crassipes) and the Common carp (Cyprinus carpio) which feature on the top of the NBA listing.
Incidentally, both the Water hyacinth and the Common carp features as one of the worst invasive alien species of plant and fish respectively all across the globe. Europe, Africa, the Americas and Asia all have the water hyacinth on the top of their list of nuisance plants. The Asian carps are listed as one of the worst nuisance fishes in Europe, based on their threats on native fish species.
The question placed on the table, therefore, is whether the State administration is ready to take up the challenge posed by the invasive, alien species of plants and animals, more particularly their observed threats on ecosystems, native species of plants and animals, and the livelihoods of wetland dependent local communities.
