Could Your Pet Be an Invasive Species?

Contact: Ruth Hanessian |

Could Your Pet Be an Invasive Species?
Burmese python – Florida
Photo: Roy Wood, NPS,

ANNAPOLIS, MD (November 2, 2009) – Perhaps. It’s up to you to ensure that Fluffy the cat, Frodo your pet frog and his aquatic hydrilla plant do not become one of the many non-native species that have become established and invasive in Maryland. In some cases, these non-native species are competing with our native flora and fauna, at times forcing them towards extinction. For this reason, the Maryland Invasive Species Council has chosen domestic pets as November’s POTENTIAL Invader of the Month.

Invasive species arrive from different sources, some very well intentioned. Kudzu, (Pueraria montana var. lobata), a rapidly growing vine widely known as “the vine that ate the South” was introduced to the U.S. at the 1876 Philadelphia Centennial Exposition as an ornamental and potential forage crop. The Federal government encouraged farmers to plant kudzu to stabilize and improve soil conditions. Kudzu worked too well and engulfed thousands of acres of farmland with its dense aggressive growth.

The fur industry in Maryland was boosted by the introduction of nutria (Myocaster coypus), a South American aquatic rodent. The initial imported animals escaped captivity and established sizable populations, which now happily feast on marsh plants in Chesapeake Bay wetlands. Nutria feeding zones called “eat outs” and their tunnels through earthen dams damage marsh habitat and reduce food for native species, including migratory birds. Ultimately, nutria weren’t popular enough to make into coats, so fur industry demand has not controlled their destructive population. Maryland spends thousands of dollars annually to try to control these invaders.

Another well-intentioned introduction was a small group of starlings released in Central Park in New York City in the late 1800s. Cavity nesters, they multiplied rapidly and now extend all the way to the West Coast. They successfully compete with our beautiful native bluebirds for nesting sites. Bluebirds had disappeared inside the Washington Beltway until a single individual, Dr. Larry Zeleny, began providing protected nest boxes on bluebird trails in Greenbelt. Now, as a result of his efforts and those of other bluebird enthusiasts, you can enjoy beautiful, insectivorous bluebirds not only inside the Beltway, but in open backyards in the whole area. This is how one person — YOU — can make a difference!

Pets are an integral part of the lives of well over half the U.S. population. From the goldfish won at the County Fair to a bird costing thousands of dollars that will live far longer than its owner, pets in all shapes and sizes provide companionship and joy to us.

Sadly, there are times when a new home must be found for a pet. Humane societies, rescue groups and many local pet stores will all help you “re-home” your pet. But NEVER, NEVER, release a pet to the wild and “let nature take its course.” An animal that has lived with you for a period of time, even if you originally found it in your own backyard, should not be released. It will no longer be able to live successfully in the wild. A gerbil’s chances of surviving surrounded by foxes and raccoons, hawks and owls, not to mention the neighborhood dog or cat, are slim. (California, however, is so concerned that gerbils will become established as pests in agricultural fields that owning gerbils in California is illegal.) Currently, Burmese pythons (Python molurus bivittatus) and rock pythons (Python sebae), which began their lives as exotic pets in private homes in Florida, are found in increasing numbers in the Everglades. State biologists report that they are consuming native wildlife in addition to dogs and cats and worry that they are now reproducing in south Florida. These snakes are both constrictors, and are large enough to be a risk to people, especially young children. The ponds at the Everglades Visitor Center are populated with oscars, (Astronotus ocellatus) an aggressive aquarium fish native to South America, not to Florida.

So, what are the risks for your pets? Cats that reproduce outdoors develop into colonies of feral cats that consume more than mice. Our native birds are at high risk, especially the ground nesters like killdeer (Charadrius vociferous). And when feral cats come into contact with our house pets, diseases and parasites can quickly be spread to our pets.

Your parakeet with untrimmed wings that flies out the front door will probably be eaten by a hawk. However, Quaker parakeets (Myiopsitta monachus), a colony-nesting South American bird, became established from groups of birds that escaped from pet facilities. They are now happily breeding in Rehoboth, Chicago and Brooklyn. Quaker parakeets build large stick nests and have a preference for warm electrical transformers. This nesting behavior, all too often, results in fires and electrical outages for adjacent homes and businesses.

Northern snakeheads, those frankenfish (Channa argus), that got so much publicity when they were found in ponds in Crofton in 2002, and more recently in Wheaton Regional Park and the Potomac River, may not have been the species you have in your aquarium. They probably came from Asian markets that sell live food, although the actual source of the introduced animals is unknown. Because of the danger this voracious species poses to Maryland’s freshwater environments, the state approved regulations banning the possession of two snakehead species and the introduction into the state of the entire biological family snakeheads belong to, Channidae. As a result, some attractive species of Channidae found in the pet trade are no longer legal in Maryland. While some members of the pet industry believe that the regulatory response to northern snakehead was too broad, those regulations would not have been promulgated if these exotic fish had not been released in the first place.

What should you do with any pet you cannot keep? Contact your local Humane Society, rescue group or your local pet store for guidance. DO NOT RELEASE IT INTO THE WILD! It will not come to a happy ending, either starving to death or being eaten by a predator. Or it may survive, establish and become the next invasive species damaging our land. The seemingly innocent act of dumping a goldfish bowl into a pond may introduce not only your pet and plants but associated microorganisms that can run amok in our native aquatic ecosystem.

Birds that usurp nesting cavities from our beautiful insect eating bluebirds, fish that prey on our newly hatched gamefish, plants that impede navigation on our waterways — all have resulted from the unintentional release of pets.

As the wild places in Maryland increasingly compete with our expanding human populations, the need to be responsible with all animals, both captive and free, gives each of us an opportunity to enjoy and understand the complexities of the environments necessary for survival for people and other animals. This challenge is one that each one of us cannot only meet but encourage others to share for the benefit of our world.


  • Commit to keeping a pet for its complete life span.
  • Keep your pets safe and under your supervision.
  • Enjoy the privileges we have to keep a wide variety of appropriate pets in Maryland.
  • If you can no longer be responsible for your pet, be responsible for finding it a safe new home.
  • EVER release a pet into the wild, EVER!


For more information about this and other Invasive Species of Concern, visit

photos available electronically on request.