According to the phys.org website domestic, stray and feral cats are the third most costly invasive species on the planet. To be clear their scientific name is Felis catus. The infographic below tells us that the cumulative cost of costs between 1970 and 2017 in billions of US dollars is 51.6. This is dwarfed by mosquitoes costing hundred US$148.7 billion.
Cats are the third most costly invasive species. Infographic: phys.org.
Of course, the reason why cats are invasive species is because of people. We made this rod with which to punish ourselves. It all started when people began to travel on ships to far-flung countries and they took their domestic cats with them. Romans brought domestic cats to the United Kingdom in around 200 A.D. We don't refer to them as invasive species, by the way, in the UK. This is probably because they're not invasive species as the wildcat once lived in the UK and the domestic cat is a domesticated wildcat.
They say that the domestic cat is one of the worst invasive species and that it has been taken across the world for hundreds of years. The cat is "invasive in almost all the islands of the world" according to Franck Courchamp, director of the Paris-Saclay laboratory.
He said that they have been responsible for "the most killings in the world of birds, reptiles and amphibians, which are not prepared for this type of predator."
In general, they concluded that there has been a 70% increase in invasive species since 1970 in the 21 countries where they studied them. In all, invasive species have cost nearly US$1.3 trillion to the global economy since 1970. This is an average of US$26.8 billion annually. The figure is probably an underestimate.
Most of the financial damage is caused by damage to ecosystems, fisheries and crops.
My mind is inevitably drawn to Australia, a continent to which cats were introduced by the early settlers in the 1700s. They brought with them some domestic cats. They badly managed them and they became free-living cats. These became feral cats. They procreated on a continent abundant with the kind of prey animal that cats feed on such a small mammals. Now the authorities don't know how many feral cats there are in Australia but they are in the millions.
They are very concerned about the impact that they have on conservation. As a consequence they do all they can to kill them as fast as possible. It is a pet hate of mine because there must be better ways of reducing the population of feral cat than inhumane poisoning, shooting or any other method of killing which they employ. Camels have also been introduced to Australia and they are in the wild as well.