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Biodiversity Blog


Pets as Invasive Species, an Introduction

two cats
Lucy (back) and Olive (front), two out of three of the author's feline invasive species.

Humans have pets for lots of reasons. Companionship, protection, admiration of the animal’s beauty, an excuse to get outside for a walk. As much as we don’t want to hear it, our beloved Fido or Snowball, when mismanaged, can become invasive and threaten biodiversity. In this new series, we will look at some of the common pets we own, explore how they have become invasive, and what we can do to slow or stop their harm to natural environments.  


We first have to understand what an invasive species is. Most species are native to someplace, and within those places of origin, they generally live pretty harmoniously. It’s also important to note that not all non-native species become invasive when they manage to get out of their normal habitat. For example, if someone in Alaska releases a pet budgie (Melopsittacus undulatus), a small bird native to warm Australian grasslands, that creature will eventually become a bird popsicle. It’s just one example of how some species can’t survive the climate or live off the available food or water in non-native territories. But for those that find their new environments more than hospitable, it’s a different story.

A species is considered invasive when it is non-native to an area, adapts and reproduces quickly, and out-competes native species for resources. In short, when it has a negative impact on an ecosystem. Invasives can introduce diseases to native populations. They also can harm economies by causing decline in other species we use as resources or food. Controlling them can cost governments millions of dollars. 


Promoting the cactus moth in Australia in the early 1900s (State of Queensland, Dept. of Agriculture and Fisheries)

Many invasive species are introduced accidentally. Just a few of the many ways include insects hitching rides on landscape plants and shipping vessels unknowingly transporting aquatic species. However, many species are also introduced deliberately by people who may not understand the implications of their actions, even if their intentions are sometimes good. For example, some species become invasive once they are introduced as a method of biological control of other invasive species. 

An example is the introduction of the South American cactus moth, Cactoblastis cactorum, to Australia in the 1920s. It was brought in to control the North American prickly pear which had become an invasive weed by the early 1900s, infesting millions of hectares. Because of the moth’s success in decimating the cactus, it was introduced to other parts of the world. Things got out of hand, to put it mildly. Right now, this moth is wreaking havoc to native prickly pear species (Opuntia) across the southwest US, including Texas. The moth could potentially wipe out prickly pear cacus entirely. Brackenridge Field Lab is studying ways to keep it under control before it’s too late.

Collecting Cochineal
1777 illustration of cochineal collecting (José Antonio de Alzate y Ramírez, Newberry Library, Edward E. Ayer Manuscript Collection)

Interestingly enough, the story of this cactus in Australia also serves as another example of how humans are great drivers of introducing invasive species. In the late 1700s, the prickly pear was introduced in the Land Down Under to establish a cochineal industry. Female cochineal insects (Dactylopius coccus) cluster on cactus pads where they feed. They also produce an acid that creates a deep red color known as carmine. The bugs are harvested from cactus pads, dried, and ground up to use for dyeing. Historically, carmine was so coveted by the wealthy and powerful, that Spain established explotative industries in the "New World" to monopolize it. Even pirates ransacked ships to acquire it. The Australias aspired for their own cochineal industry, but had no native prickly pear to feed the little bugs, and thus the introduction of a non-native plant that soon became a nightmare.

Beyond bugs and cactus, humans also introduce species we tend to covet a little more, those species being our pets. We start with fish, then take a look at cats and dogs. Not to be outdone are reptiles and amphians and birds.



Carman, Katie. “How Carmine, the Red Dye Made from Bugs, Makes It Into Your Food.” How Stuff Works. February 18, 2021. (accessed online: https://recipes.howstuffworks.com/food-science/carmine.htm)

National Wildlife Federation: Invasive Species (accessed online: https://www.nwf.org/Educational-Resources/Wildlife-Guide/Threats-to-Wildlife/Invasive-Species

Resource Library, Encyclopedic Entry. Invasive Species. National Geographic (accessed online: https://www.nationalgeographic.org/encyclopedia/invasive-species/)

Spencer, Erin. “Let’s Talk About Pets” January 20, 2016. Invasive Species Initiative (accessed online: http://www.invasivespeciesinitiative.com/from-the-field/2016/1/29/lets-talk-about-pets)

“The Prickly Pear Story” June 20202. The State of Queensland, Department of Agriculture and Fisheries. (accessed online: https://www.daf.qld.gov.au/__data/assets/pdf_file/0014/55301/prickly-pear-story.pdf)


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