The Polish Academy of Sciences has compiled a database of invasive species, currently listing more than 1,700 entries. Recently, the domesticated house cat, Felis catus, was included in this list, stirring significant debate online. Many cat enthusiasts are bewildered by this classification, viewing it as harsh or unfounded.

However, scientists argue that this categorization is both accurate and important. To clarify, let’s start with the definition of a cat. The term itself can be nebulous, given that there are over 50 recognized breeds, yet they all belong to a single scientific classification.

In 1758, Carl Linnaeus assigned the name Felis catus to the common domestic cat. Although Felis catus domesticus was suggested in 1777, Linnaeus's original term has remained more widely accepted. The International Commission on Zoological Nomenclature reaffirmed this classification in 2003, but subsequent genetic studies in 2007 proposed that Felis silvestris catus, a subspecies of the European wildcat, might be a more fitting designation. By 2017, the entire Felidae family underwent a revision, leading to the re-establishment of the name Felis catus.

From an evolutionary standpoint, domestic cats likely descend from Felis silvestris lybica, a wildcat native to the Middle East. The classification of these taxa is complicated by the fact that various wildcats can interbreed. Additionally, cats have been domesticated multiple times across regions, including Asia and the Fertile Crescent.

Fundamentally, the modern house cat is a product of the Fertile Crescent. Therefore, any cat found outside the Middle East can be considered alien to that ecosystem. For example, if an American Bald Eagle is transported to Australia, it is regarded as an alien species; similarly, kudzu introduced to the U.S. qualifies as an alien organism.

The term invasive suggests that a species has the potential to reproduce rapidly and adversely affect native ecosystems. Kudzu, for instance, thrives in the southern U.S., outpacing local flora and obstructing their access to sunlight.

Invasive species, whether flora or fauna, often pose a greater threat than native species, which have evolved alongside their predators and competitors, resulting in a natural balance. In contrast, alien species may lack these checks and balances.

For example, American songbirds did not evolve with Felis catus, making them particularly vulnerable to predation by these cats. Globally, at least 40 bird species have gone extinct due to cats, a number that rises to 63 when including mammals and reptiles. Thus, domesticated cats are undeniably an invasive and alien species in many regions, posing a significant risk to numerous endangered species.

Feral cats—those that do not have human owners—present a major challenge. Although they have domesticated brains, they live independently, which is why they are termed feral rather than wild. Other species, such as pigs and dogs, can also become feral.

This raises an important question: what should we do about these charming yet deadly cats? The Polish Academy of Sciences has faced criticism for its stance, which essentially advocates for cat owners to keep their pets indoors more, particularly during bird breeding seasons.

I would argue that cats should ideally be indoor pets unless they are supervised, on a leash, or working as barn cats. This recommendation allows for rare exceptions, such as feral cats that may never adapt to indoor life. Some people have successfully tamed strays enough to take them to the vet for spaying or neutering, but these cats may still prefer outdoor living.

Let’s consider outdoor cats as a transitional phase—either we are helping them adapt to indoor life or working to care for the local feral population. Our goal should be to strive for indoor-only cats.

However, outdoor enclosures known as "catios" and leashes are available for those who wish to give their cats supervised outdoor experiences. For instance, JJ, my cat, is terrified of loud noises, so he can enjoy the porch under the watchful eyes of two adults.

I understand that some may argue it’s cruel to keep cats indoors all day. Yet, as long as you engage with your cat through play and enrichment activities, it is not cruel at all. Enrichment can come in many forms—from designated cat spaces on desks to climbing towers.

We also provide cat-safe plants and occasionally allow our cats to chase bugs that enter the house. JJ often catches them, celebrating his victory by devouring his prize.

Managing multiple cats is easier for us as our three get along well. Although we experimented with bringing in a fourth cat, the dynamics were problematic, leading us to find new homes for them.

Indoor cats can lead fulfilling lives, but we must make sacrifices to support the overall ecosystem.

So, how should we address the issue of feral cats? There are three primary approaches:

1. Support the feral population: Providing food for feral cats often leads to increased populations.
2. Trap-Neuter-Release (TNR): This method involves trapping feral cats, spaying or neutering them, and then returning them to their original locations. While this can stabilize populations, it does not eliminate the issue entirely as new cats may be introduced.
3. Euthanasia: This is a more drastic measure that Australia is considering, as it effectively reduces feral cat numbers.

In light of the ongoing extinction crisis, particularly in unique ecosystems, the option of euthanasia may increasingly seem necessary. I personally dislike this notion, but the dilemma of whether to eliminate feral cats or risk the extinction of an entire species is a significant ethical challenge.

Most people struggle to separate their emotions from the discussion, as they may visualize their beloved pets rather than considering the ecological impacts. If we can effectively manage feral cat populations through responsible pet ownership—ensuring all cats are spayed or neutered, vaccinated, and cared for—this would be a positive outcome. However, if those efforts fail, we may have to resort to euthanasia as a last resort.

To help avoid this situation, here are some actionable steps:

• Ensure all your cats are spayed or neutered unless you have a well-researched breeding plan.
• Keep your cats indoors; their whining at the door is preferable to the harm they could cause.
• Engage with your cat through play and provide enrichment options that don’t rely solely on your presence.
• Encourage others to keep their cats indoors as well.
• Keep your cat’s health up to date, as indoor cats tend to live longer and require medical care.

Instead of merely commenting on this topic, I encourage you to devise a plan to make your cats indoor pets. If they’re already indoors, consider adding enrichment activities, whether that’s a new toy or a leash and harness. Then come back and share your experiences!