Problem pets: released into the wild, these animals can harm the environment.
Skip Snow, a wildlife biologist in Everglades National Park, Florida, knows what happens to a Burmese python after a few years of good care. Full-grown, it can be 20 feet long and weigh more than 200 pounds (see photo, p. 8). Snow often spends days trying to capture the big snakes, which can be strong enough to take on alligators.
"The python problem [in the Ever-glades] started with pet snakes," Snow says. "People let them go because they grew too big--or they escaped."
In Southeast Asia, the Burmese python's native environment, this would not have been a problem. In a stable, established ecosystem, every animal and plant species has what it needs to survive--but it also has natural predators to keep its numbers in check.
When an animal or a plant species is introduced where it doesn't belong, a lack of natural predators can cause its numbers to increase rapidly. This throws the area's balance out of whack, bringing death and destruction to defenseless native species.
That is what happened when pet owners released their Burmese pythons into the saw-grass marshes of South Florida. "The [pythons] are competing with other animals for food, space, burrows, crevices, and rocks," says Snow.
South Florida is not the only place in the United States that is struggling with former pets that have become invasive species. Here are some other problem critters.
Nile Monitor Lizards
With their blue tongues, beaded skin, and daggerlike claws, Nile monitor lizards are prized exotic pets. But, like Burmese pythons, when these animals become full-size, their owners sometimes release them. Nile monitor lizards are now living in canals in Cape Coral, Florida, and may be migrating to other areas.
Experts say that the lizards, which can grow to be seven feet long, have a nasty temper and a fierce bite. So far, the creatures haven't hurt any humans, but small pets are in danger. Wildlife officials are also concerned that Nile monitor lizards may be feeding on the eggs of the endangered burrowing owl.
With their squawking and swooping, as well as their colorful feathers, monk parakeets are hard to miss. These small birds have large--and noisy--colonies in 12 states, including Florida and Texas, and in much of the Northeast. Originally from South America, monk parakeets are often kept as pets. Ecologists think that the wild colonies developed from birds that escaped or were released.
Some people enjoy seeing these tropical birds in the wild. But scientists worry that monk parakeets may be threatening native bird or plant species. Some fruit farmers in Florida claim the birds are damaging crops.
Giant African Snails
In 1966, a young boy smuggled three giant African snails into Miami, Florida. His grandmother later set them loose in the yard. The animals--about the size of an adult man's fist--spread quickly. Within a few years, they were causing millions of dollars' worth of damage to farm crops and other plant life.
Besides destroying crops, some of the snails carry a parasite that can cause meningitis (an infectious disease) in humans. Owning giant African snails is now illegal in the U.S. But they became popular as home and classroom pets, so some may still be living in pet owners' tanks. If you have one, notify the U.S. Department of Agriculture (USDA). They'll help you get rid of it safely.
How can one of America's favorite pets be an invasive species? Believe it or not, some cats are. Domestic cats are not native to the U.S. Early settlers brought them to America from other countries.
When domestic cats run wild, they are called feral. Millions of feral cats roam the U.S. They prey on native birds, reptiles, and small mammals. No one complains when cats keep the number of rats and mice in check. But in certain areas, such as Hawaii, feral cats may be driving some rare songbirds to extinction.
Not all invasive species begin as pets. Take the coqui (koh-KEE) frog, for example. The size of a U.S. quarter, this amphibian hitchhiked to Hawaii from Puerto Rico on plants. Its population exploded on Hawaii's largest island. The coqui frog gobbles up insects and spiders that are a necessary part of native songbirds' food supply.
Another invader is the northern snakehead, a fish that can be 3 feet long and weigh 15 pounds or more. Popular as food in China, it was imported live to U.S. fish markets and sold from tanks. But some were released into U.S. waterways. The snakehead devours amphibians, other fish, aquatic birds, and even some small mammals.
It's Up to You
Whether invasive species arrive as pets, hitchhikers, or fresh food, once they become a problem, it is difficult--perhaps impossible--to get rid of them. The best defense is to keep them from becoming a problem in the first place.
"If you're going to be a pet owner, do your homework," Snow recommends. "Ask, 'How big is this animal going to get, how much will it eat, and how much will it cost me to keep this pet for its lifetime?'"
If you have a pet that you can't keep--for any reason--seek help from the USDA or a state or federal wildlife agency. Don't think that it will be "kinder" to set an animal free. No matter what species it is, it is likely to cause problems or suffer them in the wild. Even that cute little Easter bunny can become a serious problem if it isn't a native species.
Words to Know
* ecologists: a scientist who studies the interrelationship of organisms [living things] and their environments.
* ecosystem: a community of plants and animals living in an environment that supplies what they need to survive and thrive.
* invasive species: species that enter new ecosystems and multiply, harming native species and their habitats.
Think About It
1. Not all pets released into the wild will become dangerous predators. What harm might befall pets that have no natural defenses against native wildlife?
2. If a pet owner can't take care of an animal anymore, where should he or she take it? Explain. What else might be done to prevent the problem of invasive species?
Web Watch: National Invasive Species Information Center www.invasivespeciesinfo.gov
Students should be able to:
* understand the consequences of releasing unwanted pets into the wild.
* Word to Know
* feral: having escaped from domestication (tamed state) and become wild.
Invasive species are a worldwide problem. As travel becomes faster, the spread of species--intentional or inadvertent--becomes harder to limit. Increasing awareness of the problems caused by invasive species and of the need for coordinated efforts to deal with them has led to the creation of a number of U.S. and international agencies, including the National Invasive Species Information Center (invasivespeciesinfo.gov), founded in 2005.
* Critical Thinking
MAKING PREDICTIONS: Which animal in this article could be most harmful to the environment? Why? (Answers will vary, but should include supporting reasons--for example, the giant African snail, because it can spread disease among humans, or Nile monitor lizard, because it eats any animal it can kill.)
DEFENDING AN ARGUMENT: Is wearing animal for or eating meat unethical? Why or why not? What rights, if any, should an animal have? (Answers will vary.)
AN IN-DEPTH LOOK: Have each student research an animal native to your area, then prepare a brief presentation for the class, answering such questions as: How does the animal get food? How does it keep away predators? What factors, if any, threaten its survival?
SOCIAL STUDIES, GRADES 5-8
* People, places, and environments: Releasing a pet into the wild can result in great harm to the natural environment.
* Silverstein, Alvin, et al., Pocket Pets (Lerner Publishing Group, 2000). Grades 4-7.
* Stein, Sara, Great Pets! (Storey Books, 2003). Grades 4-6.
* Global Invasive Species Database issg.org/database
* Invasive Species Photos news.nationalgeographic.com/news/2004/6/photogalleries/invasive
* Match each invasive species in the left column with the matching description in the right column.
--1. Burmese python A. popular as food in China --2. coqui frog B. has a fierce bite --3. giant African snail C. can grow to 20 feet long --4. Nile monitor lizard D. the size of a quarter --5. northern E. may carry a meningitis-causing snakehead parasite