DISCLAIMER: We don't own cats as we are both allergic. I'm so allergic that I take an antihistamine before I go to parties in case someone at the party owns cats. No crazy cat lady bias here.
If you live or aspire to live in a rural area in any US state except Alaska, this post applies to you. If you are or want to be in rural AZ or TX, this post could save your life. Why? Venomous snakes. Yup, there seems to be a relationship around here between the density of cats and incidence of rattlesnake bites, mostly bites of pets. My evidence is primarily anecdotal, but derived from the basics of our friend, the food chain, and the recent rattlesnake bites in our little community. We live in one of the states with a long list of poisonous snakes, so a concern for us 9 months out of the year.
First, there are people. The people have food for themselves and their animals. Some of that food, especially for horses, is attractive to mice and rats. These cute, furry purveyors of Hanna virus are also a favorite food of snakes. The more successful snakes, especially in the southern part of the US, are poisonous. If your pet comes near and threatens the food chain, pet gets bitten.
So enter the cats, especially barn cats. They do two positive things. First, they reduce the rodent population thus disrupting the food chain. Second, they will kill smaller snakes, thus interrupting the growth and reproduction dynamics of the snakes.
There is a caveat. The cats will also kill your beautiful song birds. For some reason, they prefer the beautiful birds to the exotic doves, house finches and sparrows. There is a bit of a solution for this. My wonderful neighbor does the opposite of most cat owners because she understands the food chain. Most rodents are nocturnal, so she keeps her cats inside the barn during the day and allows them out at night. Yup, only the smartest cats survive the owls and mountain lions, but the number of snake sightings in our area seems to be trending down.
In 20 years we have seen one snake on our property (knock on wood) and it was a garter snake. We are surrounded by cat owners. Coincidence? I think not!