St. Patrick's Day honors a 5th-century saint who not only spread Christianity in Ireland, but also supposedly ridded the island of snakes by herding them out to sea. As a popular Irish folk song puts it, "Success to bold St. Patty's fist / he was a saint so clever / He gave the snakes and toads a twist / and banished them forever."

Is that true? Did St. Patrick really banish all snakes (and toads) from Ireland?

Not exactly. Ireland didn't have snakes in the first place, due to its geographic location and glacial history. When snakes first evolved 100 million years ago — slithering around the ancient supercontinent of Gondwanaland — Ireland was still underwater. As continents drifted and sea levels changed, Ireland eventually rose up from the Atlantic, and was even briefly linked to Britain and mainland Europe by land bridges. But as the Smithsonian Institution explains, "any snake that may have slithered its way to Ireland would have turned into a popsicle when the ice ages hit."

Perennially frozen ground is unkind to cold-blooded animals, so Ireland stayed snake-free until it finally thawed about 15,000 years ago. And while snakes could have invaded after that, there was still one problem: the ocean. Thanks to 12 miles of chilly seawater separating it from Britain, Ireland is now one of just five major landmasses on Earth with no native snakes, joining Antarctica, Greenland, Iceland and New Zealand. As for toads, Ireland still has one species, the natterjack, that apparently arrived within the last few millennia and survived St. Patrick.

But if Ireland never had snakes, and still has toads, how did St. Patrick get credit for expunging both? His other claim to fame is converting Irish pagans to Christianity, a religion that literally demonizes snakes. And according to the Straight Dope, snake symbols were associated with some Celtic goddesses as well as the Irish cult of Crom Cruaich, which involved human sacrifices to a serpent deity.

St. Patrick therefore didn't chase away real snakes; he chased away symbolic ones. This became muddled over the centuries, though, giving rise to the popular image of St. Patrick the snake slayer. (The toad part could just be a mistranslation — "paud" meant toad in the old Norse language, so Vikings may have assumed "St. Paud-rig" was famed for eradicating toads.) And that's a shame, since there's no evidence St. Patrick held any animosity toward reptiles (or amphibians).

So in light of all the serpentine confusion St. Patrick's Day can generate, here are five important facts to remember about snakes:

1. Snakes regulate rodents

Snakes are highly efficient predators, and eat many animals that people consider pests. Perhaps the best examples are mice and rats, which have a long history of infesting our buildings and stealing our food. A worker at a Florida dog kennel learned this the hard way, as detailed in the following report by a state biologist:

"A dog kennel worker took it upon himself to eliminate all of the snakes at his place of work. Once the rat snakes had been killed, the roof rat population exploded. It took two years, hundreds of people-hours, and thousands of dollars to get control of the rats and repair the structural damage the rats had caused. This does not include the hundreds of pounds of dog food the rats ate and contaminated. The economic cost of removing the rats' natural predators was obvious."
This extends beyond dog kennels, of course. Snakes suppress rodents in all kinds of environments, from industrial grain silos to backyard vegetable gardens. Many home gardeners encourage snakes as a kind of natural pesticide, and biologists in some parts of the world now release rat snakes to help farmers protect their harvests.

Snakes' pest-control services aren't limited to mice and rats, either. Populations of insects, slugs, leeches, fish, frogs, birds and lizards can all be subject to snake management, often with snakes eating adults as well as eggs and infants. Some snake species could have even helped out St. Patrick — the hognose snake and rubber boa, for example, are known to eat toads and other snakes, respectively.

2. Snakes help control disease

By regulating rodent populations, snakes also benefit people by keeping infectious diseases in check. As the U.S. Centers for Disease Control and Prevention point out, rodents (and their insect parasites) are infamous for spreading illnesses that can infect humans, including bubonic plague, hantavirus, hemorrhagic fever, leptospirosis, rat-bite fever, salmonellosis, South American arenavirus and tularemia.

3. Snakes indicate ecosystem health

Snakes are an upper-level predator in many ecosystems, often serving as a keystone species that, as the Nature Knowledge Project defines it, "exerts top-down influence on lower trophic levels and prevents species at lower trophic levels from monopolizing critical resources, such as competition for space or key producer food sources." The presence of keystone predators is typically a good sign for an ecosystem, implying an abundant — but regulated — food supply toward the base of the food web.

4. Snakes are inherently scary

Most snakes aren't venomous, and those that are mainly use venom to subdue prey, not for self-defense. Still, a bite from some species can maim or kill people, so it's worth knowing which snakes live in your area. And being scared of snakes shouldn't be embarrassing — a recent study found humans' fear of snakes may be genetic.

Sometimes a natural fear can become an unhealthy fixation, though, which some animal-rights advocates say applies to the U.S. tradition of rattlesnake roundups. Parodied as "Whacking Day" in a 1993 episode of "The Simpsons," mass snake hunts are still practiced in a handful of states, including the premiere Sweetwater Rattlesnake Roundup in central Texas, reportedly the world's largest. While supporters of rattlesnake roundups say they're harmless, environmental groups argue they're partly responsible for declining populations of Eastern diamondback rattlers.

5. Snakes aren't good tourists

Snakes may benefit their native ecosystems, but they often have the opposite effect when traveling. Invasive snakes have been especially harmful after hitchhiking on ships to small islands, devastating already-tiny populations of native birds in places like Guam and Hawaii. Pet snakes are another threat — a variety of pythons are now annihilating native wildlife in the Florida Everglades, for example, many of them exotic pets that escaped during Hurricane Andrew in 1992.

But in the spirit of St. Patrick, wildlife authorities around the world are working to rid their local habitats of alien snakes and other invaders. One campaign in Australia even shares St. Patrick's reputed distaste for toads — cane toads, specifically, an invasive and poisonous species that kills native animals. The annual Toad Day Out is held March 29 in an effort to eradicate cane toads from Queensland.

For more about St. Patrick and snakes, check out this Irish folk song, "St. Patrick Was a Gentleman," and the related links below:


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