Squirrel vs. Rattlesnake
I pronounce 2020 to be the Year of the Squirrel.
This is not an official zodiac designation. While the TV news stations report whimsical stories of dolphins swimming through canals in Venice and sika deer taking over subway stations in Japan, we Californians need look no further than our front yards for evidence that certain wildlife species are having a much better year than most of us humans.
Earlier this spring, ground squirrels moved into a yard up my street from a nearby natural area. They’ve been steadily spreading down the block ever since, digging their little burrow cities into the bases of neighbors’ lavender bushes. Much to the dismay of my very prey-driven dog, a scurry of squirrels (the official name for a group of these critters) has now moved into our front yard and is busily undermining our concrete driveway.
Why the fuzzy beasts are doing so well this year is anyone’s guess. It might be the heavy rain we got last year, it might the new delicious things planted by people stuck at home due to the COVID-19 lockdown, or it might be something else.
One thing is clear, though: 2020 is also the Year of the Rattlesnake, and it’s no coincidence that squirrels and rattlesnakes are flourishing at the same time.
I am a scientist who has studied rattlesnakes for over 20 years, and I also own a small business relocating rattlesnakes from people’s yards. Everywhere I went this spring, people lamented the sudden appearance of rattlesnakes, often multiple individuals, in their yards. While this could also stem from last year’s rains or from the fact that people are spending more time in their yards than usual, there is another obvious explanation.
Where there are ground squirrels, there are rattlesnakes.
Despite their tough guy reputations, rattlesnakes are very sensitive to exposure to the elements and rely on rodent burrows to escape the heat and the cold. When my students radio-track rattlesnakes for their research, they consistently report rattlesnakes taking shelter inside ground squirrel burrows, sometimes even overwintering in them. Rattlesnakes also like to eat ground squirrels, especially the succulent young ones.
But the lives of ground squirrels and rattlesnakes are interwoven in far deeper ways as well.
Locked in a conflict for survival, ground squirrels have evolved resistance to rattlesnake venom over the millennia. Rattlesnakes that happened to have more toxic venom got to eat more squirrels than those that didn’t, then had more babies who also had the highly effective venom, who in turn got more food, and so on. Meanwhile, squirrels that happened to have immune systems that made them resistant to venom were able to survive a snakebite and have lots of babies, thereby passing on genes for resistance to the next generation. It’s a textbook example of natural selection leading to local adaptation of predator to prey, and vice versa.
Incredibly, the ground squirrels seem to know they are resistant, in that they can often be seen harassing rattlesnakes by throwing dirt at them, even running up and biting them. You read that correctly: squirrels bite rattlesnakes, and sometimes even kill them.
When they see a rattlesnake nearby, the cheeky rodents wag their fluffy tails back and forth rapidly, a behavior known as “tail-flagging.” A closer look at this behavior using a thermal imaging camera revealed a jaw-dropping biology story: while tail-flagging at a rattlesnake, squirrels shunt additional blood into their tails, causing them to heat up. We humans need the imaging camera to see what the heat-detecting pits on a rattlesnake’s face allows it to sense: the squirrel’s flagging tail lights up like a light saber when they wave it at rattlesnakes.
The squirrel seems to be telling this ambush predator, “Hey, I see you. You can’t sneak a bite at me and you certainly can’t come down this hole and get my babies, so skive off.” Indeed, after being tail-flagged at by a squirrel, rattlesnakes often leave the premises and find another spot to hunt.
Squirrels have more rattlesnake-related tricks up their furry sleeves, too. If they find a rattlesnake’s shed skin, they chew it up and rub it all over their bodies. This behavior puzzled scientists until they discovered that rattlesnakes appear to be disinterested in trying to bite and eat squirrels that have applied the snake scent.
You’d be right at this point to think that ground squirrels are “winning” the war with rattlesnakes… I mean, they are sometimes resistant to venom, they use snake-scented invisibility cloaks to hide in plain sight, and they confront rattlesnakes with light saber-tails.
But who is winning in the court of public opinion?
Let me set a scenario for you, as a thought exercise. Imagine two animals inhabiting a nature preserve. One animal is rarely observed because it hides from people, but is known by scientists to protect plants at the preserve, provide important food to the hawks and falcons we all love, and eat critters that carry serious diseases that could otherwise infect people. Heck, it even inspired the invention of a life-saving drug. The other animal, more commonly observed by people in part due to its habit of begging for food scraps, is one of the disease-carrying critters kept under control by the first animal.
Based on this information alone, which animal would you think is loved by most people, and which is hated?
You would be wrong.
The first animal is a Northern Pacific Rattlesnake. They protect plants by eating lots of vegetation-noshing animals that would otherwise chew them down to nubs. Furthermore, mice eat lots of seeds, which are baby plants. Their stomachs digest the seeds, and the mice absorb and use the nutrients. But if a rattlesnake eats a mouse that has recently consumed a seed, the snake’s stomach effectively rescues the seed from being digested, and it poops the seed out in a week or two in a little pile of fertilizer where it will later germinate. Rattlesnakes are regularly eaten by hawks and falcons, as well as other top predators like badgers, foxes, and coyotes. Last but not least, an important drug preventing blood clots in at-risk patients has been developed from rattlesnake venom, and the rich cocktail of proteins in their venom shows promise for inspiring many more pharmaceuticals.
The disease-carrying animal is a California ground squirrel, which eats seeds (and your prized tomatoes) for a living. It also carries the bacteria that cause plague. That’s right, plague, as in the deadly disease that killed hundreds of millions of people in the 6th and 14th centuries. A handful of people in the United States become infected with this bacteria each year, mostly when they are bitten by fleas from ground squirrels and other rodents. Antibiotics can now successfully treat this disease.
But still… ground squirrels carry plague, people!
These facts don’t match the two animal’s public image. Many people think ground squirrels are cute, with their fuzzy tails, huge black eyes, and adorable chirping noises. Dozens of children’s books about cute squirrels indoctrinate us with squirrelly charm early in life (there are only a few about rattlesnakes, and most parents wouldn’t buy them for their kids). One squirrel lover even waxes poetic about the soft fur on squirrels’ inner thighs (regrettably, snakes have no thighs).
In contrast, the vast majority of folks find rattlesnakes to be repugnant, terrifying, or both. Snake phobias are one of the most common ones out there. A recent study found that people find snakes both scary and disgusting, even more so than rats, bats, and ants, which are notorious for getting a bad rap.
Rattlesnakes are shamefully misrepresented as bite-hungry assassins by unscrupulous television networks that dupe viewers into believing they produce documentaries. As a result, many people think rattlesnakes are lurking in wild areas waiting for the chance to bite them, when in reality they are more scared of us than we are of them. Fear of snakes is mostly learned rather than instinctual, with kids picking up on cues from these television programs and from fearful adults.
If you know someone who “hates” squirrels, it’s probably just because the little pests steal seed from their backyard bird feeders. Or maybe the person you know is a farmer. Oh, how they despise ground squirrels! A 1998 study found that ground squirrels cost California up to 20 million dollars annually in ruined crops, stolen animal feed, and infrastructure damage (undermining buildings, levees, and dams). At my university, the ground squirrel population living next to the dairy facility consumed over 2000 lb. of animal feed in a single month! Sometimes tree squirrels are portrayed as environmental stewards because they bury and forget nuts, causing trees to germinate. But ground squirrels regularly kill trees by chewing the bark off of them. (Compare that to your seed-spreading rattlesnakes, just sayin.’)
Most people like squirrels and hate rattlesnakes, despite the fact that squirrels are far more destructive and arguably more dangerous to have near your home or farm than rattlesnakes.
This is true even if you’re more worried about snakebite than you are about a ground squirrel eating your tomato plants, because having ground squirrels near your property dramatically increases your chance of having rattlesnakes nearby, too.
I am certainly not minimizing the severity of a snakebite, which is a serious medical issue. There are about 8000 venomous snakebites annually in the United States, with about 5 deaths, often due to failure to seek immediate medical attention. Furthermore, the high cost of medical treatment for a snakebite can bankrupt an uninsured or underinsured victim. That said, following the simple rule of always watching where you put your hands and feet practically eliminates snakebite risk.
I’ve tried to convince you that our perceptions of ground squirrels and rattlesnakes are both a bit skewed. Did I change your opinions at all, even a little? My goal was not to make you hate or fear squirrels. You’re even less likely to get plague from a ground squirrel’s fleas than to get bitten by a rattlesnake, but the point is that you’re exceedingly unlikely to experience either.
Yet if squirrels and rattlesnakes are locked in a war, the rattlesnakes are losing the Battle of Public Relations.
At annual rattlesnake roundups in the United States, thousands of rattlesnakes are captured from the wild using ecologically disastrous methods like pouring gasoline into their dens to force them out, then are slaughtered. As if that’s not bad enough, parents encourage their children to dip their hands into the snakes’ blood and decorate the wall with gaily signed handprints. The cycle of fear and hatred continues.
Ground squirrels and rattlesnakes both have a right to exist without our approval. They do not need to be cute or useful to share the planet with us.
Many of us might not want them to share our yards, of course. But no matter what your opinion is about squirrels and rattlesnakes, neither of these animals deserves to be poisoned in their burrows or beheaded with a shovel when they venture into our space.
But sometimes our approval can give an animal a public image boost, which is exactly the goal of this article. Rattlesnakes protect plants, control disease, inspire life-saving drugs, and do not bite unless provoked. They can live for over sixty years, they spend time with family and friends, and they can feel pain, learn, and remember. Rattlesnake mothers give birth to live young, complete with little umbilical cords attached to placentas, and take care of their newborn young.
The next time you see a rattlesnake, stop and look. It is a fascinating and beautiful being in its own right. Admire it, give it a wide berth, and let it go on its slithery way.
