A medieval disease threatens these familiar garden pests.


Fans of Grumpy know he’s no fan of squirrels. Grumpy loathes them, in fact. They dig up plants and leave them dying on the ground. They plunder bird feeders. They rob your tomato plants and fruit trees. They chew on siding. They invade your attic. They eat your tulip bulbs. And if that weren’t enough, they now pose an even direr threat to the happy-go-lucky gardener. They could give you bubonic plague.

Oh, great.

Recently, near the town of Morrison, Colorado, a squirrel tested positive for bubonic plague. Caused by the bacterium Yersinia pestis, it’s the same disease that killed tens of millions of people in Europe and Asia during the Middle Ages. It’s also the bug that inspired the classic “Bring out yer dead” scene in the hilarious movie, “Monty Python & the Holy Grail.”

As you may know, Yersinia pestis infects fleas. When these fleas bite rodents and other animals, they pass on the germ to its new hosts who then carry it to human populations. In the case of the Black Death, the main carriers are thought to be rats. The cycle goes like this. Infected flea bites rat. Rat scurries all through a dirty, smelly town. Rat dies of plague. Fleas jump off dead rat onto live rats and people and bite them. When these hosts die, hungry fleas hop onto and bite the poor people hauling away the human corpses. Repeat this often enough and you have a bit of a “situation.”

Portrait Of Squirrel On Grassy Field
Credit: Camille Dai / EyeEm / Getty Images

Plague occurs in three forms, listed here form least to most deadly. Bubonic plague comes from a fleabite and causes swollen, blackened lymph nodes (“buboes”) in the neck, armpits, and groin. Without treatment, it kills approximately 50 to 70% of those infected. Septicemic plague occurs when the blood becomes infected either from a fleabite or handling infected animals and people. The nose, toes, and fingers turn black. (See where the name “Black Death” comes from?) Untreated, it’s nearly always fatal. Pneumonic plague is the fastest killer. Medieval reports record people infected at noon falling dead by night. People contract it by inhaling infected droplets coughed out or sneezed out by an infected person. Untreated, it’s 100% fatal.

What’s the treatment? Well, in the Middle Ages, there weren’t any effective ones, which is why about half of the population died after several waves of plague moved through. It was only the advent of antibiotics in the 1940s that provided a good weapon to fight back. Better sanitation, hygiene, and the awareness of germs also reduced plague. But it’s still around, as developments in Colorado attest.

How likely are you to contract plague? A heck of a less likely than with COVID-19. About seven cases per year are reported. Plague in the U.S. is mainly confined to rodents in the arid Mountain West. (Of course, if you live in the arid Mountain West, that may not be terribly comforting.) Most importantly, promptly administered antibiotics cure most infections.

That doesn’t mean we can let down our guard. Squirrels are scheming, bothersome creatures, pretending to love us, but always planning to steal what is rightfully ours. So keep an eye out, my friends. Rocky may be coming.