10 Animals That Are Bad for the Environment

Photo: David Blackwell/Flickr [CC by ND-2.0]

Animals play an important role in keeping ecosystems balanced, healthy and strong. Just like humans, animals can respond to imbalance with extreme behavior that can be harmful to the environment. Here are 10 animals that can be bad for the Earth when nature's balance gets disrupted. (Text: Bryan Nelson)

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Elephants are the world's largest and most powerful land animals, so it's not surprising they have a profound impact on the ecosystem. To reach food, elephants regularly break branches, uproot bushes and push down whole trees — sometimes whole strands of trees. Elephants prefer to roam across a vast territory, so forests can usually recover from the damage they cause. But when fences, farmland and human encroachment shrink the range of these magnificent beasts, elephant behavior can radically alter a limited landscape.

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The locust swarm of lore is one life phase of a type of short-horned grasshopper. It's a phase that can become a plague under the right conditions. (You might recall the one mentioned in the Book of Exodus.) The swarms can cover hundreds of square miles and consist of many billions of locusts. They are highly migratory and can quickly strip whole fields of vegetation. The swarm is initiated by a population burst caused by rain followed by drought, pushing greater numbers of the insects into a smaller area. Scientists in England and Australia say these close quarters trigger a chemical response. Unfortunately, the change also creates a domino effect — swarming locusts are driven to breed and eat at an increased rate.

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Crown-of-thorns starfish


This large starfish gets its name from the venomous, long spines that cover its body. They live among and feed on coral polyps. When the species becomes overpopulated, it can destroy vast coral reef ecosystems. In fact, widespread destruction of the Great Barrier Reef is partly blamed on these sea stars, which have experienced a population explosion over the last decade or so. The outbreaks are likely due to pollution from agricultural runoff, creating algae blooms that allow the crown-of-thorns' natural predators to get a less-thorny and easier meal elsewhere. During outbreaks, the starfish feed on adult corals and prevent the maturation of young corals.

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Daniel Schwen/Wiki Commons/GNU.

According to the U.N. Food and Agriculture Organization, cattle farming is responsible for 18 percent of greenhouse gases. Cattle emit a large volume of methane through burping and flatulence. Cattle ranching is also a major source of deforestation around the world, most notably in South America's Amazon rain forest. Driven by the growing food demands of an expanding human population, cattle in many regions of the world are overgrazing, reducing biodiversity of the ecosystem in the process.

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Common carp

Wiki Commons/CC License.

The common carp is a true bottom feeder, uprooting and disturbing submerged vegetation. These fish are notorious for altering their environment. They are most dangerous when introduced into an alien habitat and become an invasive species. They are believed to exist in all the continental states except Maine. Natural resource agencies in the United States and Australia spend millions annually to control the common carp.

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Kevin Collins/Flickr.

Goats can have profound negative effects on habitats that are not adapted to them. They can be voracious grazers, often with a taste for native scrub, trees and other vegetation, turning whole woodlands into grasslands if left unchecked. The problem has become particularly bad in places like Australia, as well as on isolated islands around the world where human populations have attempted to establish a settlement. Goats are rugged animals that can easily revert to a feral existence if allowed to do so.

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Cane toads

Sam Fraser-Smith/Flickr.

Cane toads have become wildly successful as an invasive species in Oceania, the Caribbean and the United States. Ironically, they were purposely introduced to foreign habitats to eradicate agricultural pests, and in the process they became pests themselves. These South American natives are most dangerous to native wildlife because their poison glands are toxic to birds, mammals, fish and reptiles — and anything else that attempts to eat them.

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Bark beetles


Many species of bark beetle choose dead or rotting wood to reproduce in, but several species (including the mountain pine beetle of western North America) are known to attack and kill live trees. Whole stands of forest can be destroyed if bark beetle numbers get out of control. The bugs can also be carriers of disease, as is the case with the American elm bark beetle which transmits Dutch elm disease.

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Rats are wildly successful animals wherever they live — a characteristic that make them dangerous when they are introduced to non-native areas. One primary example has been the introduction of black rats onto Lord Howe Island, a small habitat in the Tasman Sea, where much of the island's unique native wildlife has been wiped out by invading rats. Rats can also be the bearers of disease, and rat population outbreaks can cause substantial food losses, especially in developing countries.

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David Blackwell (Dilettante)/Flickr.

Of all the animals on Earth, humans are the most environmentally destructive. It is usually humans who are to blame for the major imbalances — global warming, the extinction crisis, over-harvesting of land and sea, overpopulation and industry. Fortunately, humans are capable of rapid cultural change. They always have a choice — and a chance — for change.