Growing up to half a meter in width, the Northern Pacific Seastar (also known as the Japanese Starfish) has spread from the North Pacific to the south coast of Australia. A single female can carry up to 20 million eggs. It’s just one of the invasive species that are traveling to new environments and harming native ecosystems. Scroll through the gallery to see more of the planet’s most problematic invasive species. Alamy

The humble comb jelly has no brain, stomach or bones. It eats microscopic sea organisms, as well as fish eggs and larvae. Native to the Atlantic coasts of North and South America, warty comb jellies reached the Black Sea, Aegean Sea and Caspian Sea during the 1980s. The jellies traveled across oceans in the ballast water of ships. In these new waters, they flourish thanks to a lack of natural predators. It is associated with crashes in fish numbers. Dolphin populations, dependent on fish supplies, have plummeted in the Black and Azov Seas as a result of the jelly invasion, according to the World Wildlife Fund. Alamy

Trees where these beetles lay their eggs are doomed to a slow death, as larvae gnaw away at their bark from the inside. Native to Asian countries including China and Japan, this species has reached Europe and North America, mostly through wooden packaging. They have already infested many poplar plantations in China, and have also been found in chestnut trees, willows and elms. The US Department of Agriculture has warned that the insects could devastate American timber industries and forests if left unchecked. Alamy

These creatures are indigenous to South America. They were deliberately introduced to many countries in the 1930s (including the USA and Australia) to help control sugar cane pests, like beetles. But cane toads proved to be disastrously voracious, eating anything from honeybees to dog food. An estimated 1.5 billion cane toads live in Australia alone. When attacked or eaten, they emit venom that can be fatal to wild animals and household pets alike. Studies in Bermuda show they are outcompeting native frogs. Ian Hitchcock/Getty Images AsiaPac/Getty Images

Related to weasels, polecats and ferrets, the stoat is a small but ferocious predator. Stoats have no qualms about attacking larger animals, including rabbits and chickens. European settlers took stoats to New Zealand for pest control purposes, where they wreaked havoc on native bird populations. The New Zealand Government spends millions of dollars each year protecting native birds from stoats, which feast on their chicks and eggs. Alamy

Sixty of these birds were set free in New York in 1890, in a bizarre plan to introduce to the USA every bird mentioned in a Shakespeare play. European Starlings were also deliberately introduced to regions of Australasia and South Africa to control native insect populations. Today, between 100 million and 200 million Common Starlings on six continents destroy many crops, and out-compete birds like woodpeckers in the United States and black cockatoos in Australia. However, their numbers appear to have fallen in recent decades, possibly due to intensive farming techniques. MENAHEM KAHANA/AFP/AFP/Getty Images

Its native range is coastal East Africa, but this snail has reached all continents except Antarctica. They are sold as food, pets, and for medicinal purposes, which led to their accidental introduction to the wild. In New Zealand, the Giant African land snail eats many types of local snails, as well as native plants. Phil Mislinski/Getty Images North America/Getty Images

This large deer species was brought from Europe and Western Asia to Australia, New Zealand and South America, for trophy hunting and livestock. It flourishes in a wide range of habitats and can outcompete native mammals searching for food. Jeff J Mitchell/Getty Images Europe/Getty Images

Originally from the Americas, this cactus is an invasive species in South Africa, Kenya and Australia. It grows in bristly thickets up to two meters high, and was often introduced to contain livestock. It is highly drought resistant and frost resistant, and can spread across millions of hectares of land. During an infamous spell dubbed “the green hell” in Australia in the 1920s, the cacti spread so rapidly and thickly across rural plains that people abandoned their homes and farms. The plants were tamed when authorities introduced a foreign cactus gourmet, the cactoblastis moth, in 1925. Shutterstock

Also known as the ship rat, it is native to India but over thousands of years, it spread to every continent except Antarctica by hiding in ships. These furry stowaways can devastate wildlife populations as they guzzle through native insects, bird eggs and chicks, and fruit. SANJAY KANOJIA/AFP/AFP/Getty Images

These purple-blossoming plants can spread to cover every inch of a lake, blocking out sunlight and crowding out native plants. The water hyacinth most likely originated in Brazilian rainforests, and became a popular addition to garden ponds worldwide in the 1890s. But this formidable species can double its size in a fortnight. The flowers are now found in most of the United States, and on every continent except Antarctica. MUNIR UZ ZAMAN/AFP/AFP/Getty Images

The big-headed ant first spread from southern Africa via ships during the 18th century. They are now found in both tropical and temperate regions, from Japan to Puerto Rico. They chew through electric wires as well as seeds, aphid honeydew, and other insects. As they graze, the ants can spread viruses among crops. Native spiders and weaver ants also struggle when this species infests new land. Sarefo / Wikimedia Commons