Science Says Cats Are One Of The World's Most Invasive Species. Here's Why

It can be easy to forget that the adorable bundle of fur curled up in your lap is actually a prolific hunter. There's a scientific reason that even domesticated cats bring home dead animals when let outside — it's in their nature. It is this natural disposition towards stalking and pursuit, coupled with the feline ability to reproduce quickly, that has made domestic cats one of the most invasive species in the world.

The U.S. Geological Survey (USGS) defines an invasive species as a "nonnative organism (disease, parasite, plant, or animal) that begins to spread or expand its range from the site of its original introduction and that has the potential to cause harm to the environment, the economy, or to human health." The descendants of wild cats, the domestic and feral felines we know today arrived in North America alongside colonists from Europe. Cats kill billions of birds and mammals each year in the United States alone, per Forbes. In fact, a 2016 study conducted by Proceedings of the National Academy of Sciences (PNAS) revealed that felines are responsible for the extinction of approximately 63 species.

Cats have a diet made up of approximately over 2,000 different species, providing a fairly definitive answer in the debate over whether felines are omnivores or carnivores. In 2023, Nature Communications published a study that determined that 347 of these species are endangered or extinct, with the list including birds, reptiles, and small mammals. Though they don't view them as prey, felines can even cause harm to humans.

Cats, especially those of the feral variety, can be detrimental to human health through the transmission of rabies or toxoplasmosis, a parasitic infection that result from exposure to cat feces (though this is primarily only a concern if the feline in question has eaten infected raw meat). While you likely don't have to worry about getting toxoplasmosis from scooping the litter box of your strictly indoor cat, indoor-outdoor felines could be carriers. Meanwhile, feral cats may choose to poop just about anywhere.

To add to this, unaltered outdoor cats reproduce at seemingly lightning speed. Shelters are often overwhelmed because of the constant influx of stray or unwanted felines, hence the term "kitten season," which ramps up as the weather turns warm (or remains consistent all year in more temperate climates). Feral cats typically aren't spayed or neutered, and therefore contribute to the rapid increase in number. In fact, one female cat can account for up to 180 kittens if not spayed (per Forbes). 

While the realization that felines are an invasive species might be distressing, kitty lovers can take key steps to help minimize the impact of cats on their local ecosystem. For instance, programs such as trap-neuter-return (TNR), a potentially life-saving alternative to kill shelters, seek to control the feral cat population by preventing more litters. While this approach may assist in addressing the population aspect, felines still contribute to the extinction of other species. The best way to combat their invasive nature it get your own cats spayed or neutered and keep them indoors. This will also give you the strongest chance of getting to spend as much time with your beloved pet as possible, as indoor cats tend to live for a decade or more longer than their outdoor counterparts, according to University of California-Davis (via PetMD).