The following essay is reproduced with permission from The conversationan online publication covering the latest research.
It is common knowledge, and not very surprising, that free-ranging cats eat birds and small rodents. But the extent to which they eat insects might surprise you.
We arebiologists who for many years have been trying to understand what wild or stray cats eat.
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When domestic cats—Cat cat—lLiving freely in the wild or allowed to hunt outside the houses where their owners live, they constitute a invasive specieswhich live in all ecosystems of the world, with the exception of the Antarctic continent. We wanted to know all the species they eat and to what extent free-ranging cats eat endangered or threatened species.
Over the past two decades, we have evaluated hundreds of scientific discoveries, including research into Google ScholarAnd Web of Scienceusing the keywords “cat predation”, “feral cat”, “cat diet” and “Felis catus”. For each item we found, whether it was peer-reviewed or not, we assessed whether it contained conclusive evidence of cat diet or predation. We also reviewed the reference section of each to find additional unique articles or databases regarding cat diet and predation, and included them in our search.
In total, we identified 533 unique publications (books, journal articles, theses, and agency reports) reporting specific animal species consumed by cats. The eating habits of cats are occasionally, but randomly, noted in studies. We therefore did not include them in our analysis.
Our initial work focused on a global assessment of what free-ranging cats eat around the world. Published in 2023, this paper analyzed all 533 studies on cat diet or predation events published over more than a century and found that cats ate nearly 2,100 different species animals, including invertebrates.
Of these 2,100, the International Union for Conservation of Nature Red List of Threatened Species listed 347 as “near threatened,” “vulnerable,” “endangered,” “critically endangered,” or “extinct” in 2023. Some species became extinct over the many decades covered by the data.
Most species eaten by cats were vertebrates, primarily birds, followed by mammals and reptiles. But data also indicates that at least 7% of species eaten by cats are insects and other invertebrates, particularly beetles, and less frequently crustaceans, arachnids, centipedes, snails, slugs and centipedes.
Most of the cat studies we reviewed did not report how many individuals of a given species the cats ate. So it was not clear what the total amount of insects was or how many calories the cats were getting from the insects.
Invertebrates make up more than 70 percent of all terrestrial animal species and are important pollinators, predators and herbivores in virtually all non-marine ecosystems. A lot invertebrates are in decline globally due to urbanization, habitat destruction, increased light pollution and pesticides, and climate change. We therefore delved deeper into the data to understand what invertebrates do cats eat.
Although just over a third of all studies we analyzed included invertebrates in cat diets, most of them failed to identify specific species of invertebrates. But we were able to identify 148 species of invertebrates.
Among them, two are considered threatened by the International Union for Conservation of Nature: THE Aldabran Grasshopper (Pternoscirtus aldabrae) in Seychelles and Tasmanian giant freshwater crayfish (Astacopsis gouldi), which can weigh up to 13 pounds (6 kilograms). Two others are considered vulnerable: open (Deinacrida heteracantha), an insect native to New Zealand that can be about the size of a mouse, and the Common Yabby (Destroyer Cherax), a freshwater crayfish native to southeastern Australia. Another, the Canary Islands beetle (Arhopalus Pines), is listed as “near threatened”.
We found no formal research evaluating how cat eating habits affect invertebrate populations. And for many species, they are probably not as important a factor as large-scale use of pesticides.
But it’s possible that cats are contributing significantly to the deaths of rare species or in specific locations.
Cats need a large amount of proteinup to a third of their daily diet, and invertebrates are good sources of protein.
In many places, invertebrates provide an easy food source. Whether in an urban garden or on a remote island, cats are unlikely to turn a blind eye to their available prey. And some cats may find it fun to chase, catch and eat insects even if they don’t need their food.
One of the challenges of researching this issue is that many invertebrates are relatively small, which makes direct observation in the field more difficult and may require more analytical approaches in the laboratory. And they have soft bodies, with no distinguishing features that might be easily recognized in feces or stomach contents.
However, molecular technologies can identify species using traces of DNA left in the environment by animals. Promising new studies begin to identify what cats eat analyze the DNA found in their stomach and feces. This research could help explore in even more detail what cats eat outdoors and how it affects various species and the environment as a whole.
This article was originally published on The conversation. Read the original article.
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