Did you know that the household cockroach, a common pest in the entire Indian subcontinent, came to India only in the 1960s? Scientists say the roaches (Scientific name: Periplaneta americana) set foot on the Indian shore along with wheat and grains imported from America and Europe way after the Independence.

The giant brown snails, (common name: African giant tree snail, scientific name: Achatina fulica) seen in almost every garden and park of the city after the first rains, also migrated to India from East Africa, during a flood some time between the 1950s and 1960s.

These common and bothersome creatures are part of what scientists world over identify as invasive alien species (IAS) — one of the greatest threats to biodiversity after global warming. Put simply, these are plants, animals, pathogens and other organisms that are not native to an ecosystem, and which may cause economic or environmental harm or adversely affect human health.

The World Wildlife Fund in Mumbai is currently holding a photo exhibition showcasing pictures and information on more than 70 such IAS of flora and fauna, to celebrate of the United Nation’s International Biological Diversity Day which fell on May 22. The exhibition held at WWF’s Fort office will be on till May 29 and displays shots by 26 photographers, including several wildlife experts like Varad Giri, Bhavin Joshi and Sudhir Agashe.

According to WWF’s Goldin Quadros, an organiser of the exhibition, “IAS severely affect the biodiversity, including causing a decline or elimination of native species — through competition, predation, or transmission of pathogens — and the disruption of local ecosystems and ecosystem functions. Usually they are introduced and/or spread outside their natural habitats accidentally or purposely. However, they later affected native biodiversity in almost every ecosystem type on earth.” Research shows that since the 17th century, IAS have contributed to nearly 40 per cent of all animal extinctions.

Most common IAS plants in Mumbai include the Subabul tree (Leucaena leucocephala), native to Mexico and Central America which renders extensive areas unusable and inaccessible and threatens native plants; the ‘Touch-me-not’ shrub also known as laajari in Marathi (Mimosa pudica), native to South American regions of Brazil, Colombia, Costa Rica, Ecuador, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama, Peru, known to have introduced in many country across the world as an ornamental plant has now become a pest in forest plantations, cropland, orchards and pasture. However, mimosa is used as a medicinal plant in many regions and is still widely sold.

Of animals, the most common IAS are the pigeons called the blue rock pigeon native to most of Europe, western Asia, and northern Africa but today spread across the world; feral pigs (the Sus scrofa), believed to be native throughout Europe and continental Asia as far south and east as Peninsular Malaysia, as well as to the islands of Sumatra and Java.

Pointing that the primary threats that IAS pose, Quadros said, “The problem continues to grow at great socio-economic, health and ecological cost around the world. IAS exacerbate poverty and threaten development through their impact on agriculture, forestry, fisheries and natural systems, which are an important basis of peoples’ livelihoods in developing countries. This damage is aggravated by climate change, pollution, habitat loss and human-induced disturbance.”

Anirudh Nair, an intern with WWF, added, “This is part of our efforts to promote the nature conservation and environmental protection. Through this exhibition we want to spread awareness about one of the major threats to the ecological and economic well-being of the society.”