Written by Thary Gazi Goh
An invasive species is a species that has been introduced by people and has gone somewhat out of control. These species come from other parts of the world, like South America or Africa.
Some invasive species are introduced by accident. For example, brown rats (Rattus norvegicus) were introduced through shipping. During the 70’s they were mostly confined to ports, but rapid urbanisation has allowed them to colonise the rest of the Klang Valley and Malaysia as well.
Brown rats are larger than black rats, when older people comment that rats are growing larger they are just observing a larger rat species colonising more urban areas.
Other invasive species are brought in for a purpose and then something goes wrong and it unexpectedly becomes uncontrollable. Black cobras were introduced as a way to control rats in plantations, but they started to follow humans and rats into urban spaces as well and are now one of the most common poisonous snakes in cities.
Some invasive species are escapees from various projects that people do. Many animals escape from the aquarium trade into our waterways and become dangerous to our native wildlife. Others like the Giant African land snail were brought for experimental food programs during World War II and escaped into farm pests.
Not all introduced species are bad. Species like pineapple and papaya are relatively benign and have become staples of our village gardens. But often the line between invasive and introduced is vague.