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April 1918. The war in Germany was raging overseas, but back in California, state horticulturist George H. Heck warned citizens that there were enemies here at home more destructive perhaps than some of the enemies our boys are fighting in the trenches.

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And surprisingly, he wasn't talking about spies, Germans, or even the Central Powers.

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He was talking about squirrels, California ground squirrels.

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And the people he wanted to recruit into this war? Schoolboys.

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So how does a native animal become a public enemy of the state? Enemy spotted. Who gets to decide when an animal crosses the line from wildlife to pest? In 1918, California ground squirrels were blamed for overpopulating land, destroying agricultural fields through burrowing, and even carrying the plague. And although this war on squirrels began over a hundred years ago, it honestly seems like it never really ended.

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Which raises a bigger question: what actually went wrong in the war on squirrels?

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Were squirrels truly invading California, or were humans unintentionally building the perfect environment for them to thrive?

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Welcome back to another episode of Enemies Underground. I'm one of your hosts, Jessica.

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I'm Vincent.

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And I'm Anya. And in this podcast, we'll be exploring the history of the California ground squirrel, how it became labeled as a pest, the traits that have helped it survive for centuries, and why this strange cold war between humans and squirrels still exists today. The first noted interaction between California ground squirrels, or CGS, and humans dated back to the 1800s when Native Americans occupied California land.

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And interestingly, CGS weren't viewed as pests at the time.

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Yeah, actually the relationship was pretty different from what we think of today. Native communities were able to find useful commodities within CGS. They used the squirrels for food, clothes, and coats.

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So at this point, the squirrels were more of a resource than a problem.

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Exactly. There wasn't really this idea yet of eradication or pest control that we'll see later on.

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But this relationship didn't last long.

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By the late 1800s, that relationship between humans and CGS started to completely change.

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California was going through massive shifts in land use following Spanish colonization and later Mexican governance.

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As agriculture and industrialization expanded, the environment changed dramatically, and so did the squirrel population.

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Native predators of the California ground squirrel, including coyotes, foxes, badgers, and birds of prey, were displaced from many regions.

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At the same time, huge areas of land were being cleared for farming, which unintentionally created ideal habitats for squirrel burrows and population growth.

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So ironically, the same agricultural expansion meant to support humans also helped the squirrel population thrive.

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And that's really the turning point where CGS slowly began shifting from useful resource to an agricultural pest. One of the main predators of the California ground squirrel is the rattlesnake. But surprisingly, CGS are incredibly good at defending themselves against them.

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In fact, one of their most impressive adaptations is the ability to develop resistance to rattlesnake venom, and even tailor that resistance to the specific rattlesink species in their area.

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One study compared squirrels living in rattlesnake populated areas to squirrels living in areas without rattlesnakes. When exposed to venom, the squirrels from the rattlesnake regions showed significantly greater resistance, less tissue damage, and faster healing.

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Think about how wild that is. These animals can literally adapt to the venom of their biggest predator, making them seem almost invincible.

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And here's another pretty wild fact. Female CGSs actually chew up the rattlesnake skin and lick their babies with it.

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Because rattlesnakes hunt partly through smell, covering the babies in snake scent helps hide them from predators.

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And it gets even crazier. Rattlesnakes also hunt based on heat mass, so CGSs will push blood flow into their tails to make themselves appear larger and more threatening.

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Essentially, they bluff the snake into backing off.

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California ground squirrels also have three different predator alarms depending on the threat. A loud whistle usually means an aerial predator like a hawk, basically duck and cover. A chattering call means scan the area for predators like foxes and bobcats. And the final alarm, called a tail flag, is specifically used for rattlesnakes. That signal tells nearby squirrels to start wagging their tails and go into defense mode.

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So what was the response to this massive surge in CGS populations? Well, farmers were not too happy.

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California ground squirrels would burrow directly beneath orchard trees, damaging roots and fields, while also feeding on crops and vineyards by eating leaves and berries.

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And the economic impact was huge. In 1910, consulting biologist Hart Merriam estimated that ground squirrels caused more than $10 million in agricultural losses every year across the United States, with California leading the damage totals.

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Then by 1917, California lawmakers estimated those losses had climbed to $30 million annually.

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So when it comes to expensive pests, CGS may honestly be near the top of the list.

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At first, people actually try controlling the squirrel population by eating them.

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Seriously, I mean there were entire squirrel recipes published in newspapers and cookbooks. One recipe for squirrel stewed instructed people to skin the squirrel carefully, season it with salt and pepper, cook it with some onions and flour, and even add puff pastry and butter near the end.

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There was also squirrel broiled, where the squirrel would be cooked over hot coals and basted with melted butter, pepper, salt, and vinegar.

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But in 1908, everything changed when it confirmed that California ground squirrels carried the bubonic plague.

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So naturally, the idea of eating squirrels became a lot less appealing.

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And once that happened, California realized it needed an entirely different strategy to control the population, which eventually brings us to Squirrel Week.

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By 1918, California's fight against ground squirrels had become so intense that the state had launched something called Squirrel Week.

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State horticulture leader George H. Heck organized a massive anti-squirrel campaign through the rodent control division, basically trying to recruit as many people as possible into what he called a war on squirrels.

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He even told farmers that they paid, quote, higher taxes to the ground squirrel than to the assessor, end quote, and claimed the food destroyed by squirrels in 1917 exceeded California's gold production by $8 million. And honestly, the campaign got kind of extreme. Schoolboys were encouraged to go out and kill what Heck called the squirrel army, with cash prizes of $50 for first place, about $800 today, plus runner-up prizes of $30 and $20.

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The state also printed around 34,000 posters and 500,000 leaflets telling people to, quote, kill the squirrels. Food is needed for our armies and allies, end quote, tying squirrel extermination directly to supporting World War One.

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And it worked. By the end of Squirrel Week, more than 104,000 squirrel tails had been turned in.

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But the main question on our mind is where did all this money even come from?

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And here's probably the craziest part of the entire campaign. California had actually set aside $40,000 in emergency wartime funds and used that money to help finance the squirrel campaign. So the state essentially framed squirrels as an extension of World War I and convinced citizens that killing squirrels was part of helping defeat Germany and support American troops.

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But despite all that, the campaign never happened again after 1918.

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And only a few years later, California started shifting towards completely different squirrel control strategies, moving away from public hunting campaigns and toward more systematic eradication methods.

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After World War II, California agriculture absolutely exploded, and honestly, so did the squirrel problem.

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New orchards and vineyards were planted across the state, often directly on top of traditional squirrel habitats. That meant California ground squirrels suddenly had access to huge amounts of food.

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In other words, humans had unintentionally supplied the enemy. New crops created an endless food source, and squirrel populations continued expanding. Farmers were introducing new fruits and nuts like nectarines, tangerines, pistachios, kiwi, along with different varieties of plums, peaches, and apples.

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It was an all-you-can-eat buffet for squirrels. And California ground squirrels are incredibly adaptable when it comes to food. Where there's food, there's usually squirrels.

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We actually still see this adaptability today. In a 2024 study by Smith and colleagues, researchers observed California ground squirrels preying on voles when vole populations became especially high, which was surprising because squirrels were mostly thought of as herbivores. This study showed that they can behaviorally adapt and even act as omnivores when it helps them survive.

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So while California was changing the battlefield, the squirrels were adapting to it, and that's a theme we'll continue seeing throughout this war. Every time humans develop a new strategy, squirrels find a way to survive it.

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By the mid-1900s, the squirrel problem was getting even worse as California agriculture continued expanding after 1945.

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California ground squirrels were not just destroying fruit and nut crops anymore. Chrysanthemums were hit especially hard, with squirrels sometimes destroying almost every bloom.

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And that damage translated directly into financial loss for farmers. Plus, when squirrels destroyed crops and seeds, it also affected livestock feeding and the broader agricultural economy.

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Because of these growing losses, farmers increasingly began classifying California ground squirrels as serious agricultural pests.

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At this point, California was not asking whether or not to fight squirrels anymore. The question had become what tools should be used.

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In 1962, California organized the first vertebrae pest conference through the Department of Agriculture.

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Think of it as a strategy meeting in the campaign against pests. Researchers, agricultural officials, and wildlife managers came together to discuss control methods including poisoning, fumigation, and trapping.

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The campaign against squirrels was becoming increasingly organized, scientific, and technological.

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As the conflict continued, the weapons became more sophisticated.

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Early campaigns like Squirrel Week relied on direct participation. Citizens hunted squirrels themselves. Later, poisoning and fumigation replaced the human hunters.

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But eventually, rodents began developing resistance to one of the most important chemical tools in the campaign, warfarin.

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So scientists responded by escalating the arms race.

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Researchers developed second-generation anticoagulant rodenticides, chemicals that prevent clotting, also known as blood thinners, and commonly called superwarfarins. These poisons were stronger, longer lasting, and often capable of killing rodents after single feeding.

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These compounds represented a new phase of pest control. The goal was no longer simply about removing squirrels, it was about overcoming the evolutionary defenses rodents had developed against earlier poisons.

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But every new weapon comes with consequences.

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Super warfarins did not stay confined to squirrels and rodents. Predators like hawks, owls, bobcats, and mountain lions often consumed poisoned animals and became poisoned themselves. The campaign had created collateral damage.

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And for the first time, California was forced to ask whether its most powerful tools were harming more than just the intended target.

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By the early 2000s, campaign against squirrels was still ongoing, and researchers, almost like the generals in this conflict, were still searching for the most effective strategy.

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At the 2006 Vertebrae Pest Conference, scientists essentially tested competing battle plans.

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Researchers compared broadcast baiting, where poison was spread across entire fields, and spot baiting, where poison was deployed directly near squirrel burrows. Researchers Wissen and Salmon looked at bait stations as a more targeted alternative for squirrel control. The idea was still to use the same toxic bait, but distribute it in a way that reduced accidental exposure to non-target animals.

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Researchers also noticed that spot baiting worked especially poorly in orchards, probably because squirrels already had access to so many alternative food sources.

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This study highlights a major tension in pest management policy, balancing conservation and ethical concerns with the agricultural need to prevent crop damage and economic loss.

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In other words, the conversation was shifting from winning the battle at any cost to limiting collateral damage. Bait stations became a kind of middle ground solution, something that could potentially satisfy both environmental concerns and the practical realities of controlling squirrel populations.

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At this point, we want to zoom in on one really interesting case study, the California ground squirrel conflict in Santa Monica's Palisades Park.

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Ground squirrel overpopulation there has been an issue for more than 40 years. Early on, Los Angeles County tried controlling the population through euthanasia and gassing, but animal rights groups pushed back hard against those methods.

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So in 2007, Santa Monica became only the second city to participate in a squirrel birth control program, originally started in Berkeley back in 2004.

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And in Berkeley, the program had actually reduced squirrel birth rates by around 66%. So people were hopeful that this could be a less invasive alternative to killing squirrels outright.

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Animal rights activists generally supported the plan because it focused on population control rather than eradication.

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But the study never fully happened. In April of 2007, the USDA disqualified Palisades Park because the park was considered too small to properly conduct the research.

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Which basically put the city right back at square one.

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And meanwhile, the squirrel problem had not gone away. Later that year, county inspectors issued another overpopulation citation. Actually, the fifth citation since 1998.

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After that citation, 45 squirrels were trapped and gagged.

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And ever since then, Los Angeles County had continued struggling with the same question we've seen throughout this entire story. What do you do when a native animal becomes treated as a public enemy? What happens when humans have once again changed the rules of war?

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But here's where the campaign against squirrels gets complicated. Walk through Palisades Park today, and you'll probably still see people feeding the squirrels, despite massive red signs telling them not to.

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And that's one of the strangest parts of this conflict. Humans are not consistent enemies. We target squirrels one day and feed them the next.

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On paper, treating squirrels as pests seems simple. Remove the problem, protect the land, control the damage. But in real life, humans do not always react to squirrels like enemies. That reaction can be explained by something called the baby schema effect, where animals with infant-like features make humans more likely to see them as cute, harmless, and worth protecting.

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The concept was originally developed by ethologist Conrad Lorenz, and it helps explain why this campaign was never just biological or agricultural. It was also emotional and psychological.

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Because while officials may see disease risk, crop destruction, and infrastructure damage, a person walking through the park might just see a tiny animal looking for a snack.

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In some ways, Californians are fighting two battles at once, one against the squirrel as a pest, and the other against their own instinct to protect it.

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By the later 2000s and into the 2020s, California began questioning the weapons themselves. In 2024, California Governor Gavin Newsom signed what was described as the strongest rat poison restriction in the United States. But interestingly, the policy wasn't really meant to protect squirrels themselves.

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The concern was secondary poisoning, where predators eat poisoned squirrels and then become poisoned too. Groups like the Center for Biological Diversity warned that species such as mountain lions, bobcats, owls, and hawks could all be affected.

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That's especially important because California ground squirrels are actually considered a keystone species, meaning that their presence impacts entire ecosystems. Their burrows aren't just used by squirrels. Animals like California salamanders, pocket gophers, and burrowing owls have all been observed using abandoned California ground squirrel burrows for shelter and storing resources. So, if squirrel populations disappear, other species can end up displaced as well.

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Burrowing owls specifically have an interesting relationship with squirrels. Not only do they use squirrel burrows for protection, but they also rely on squirrel alarm calls. One experiment found that squirrels initiated predator warning calls before owls about 66% of the time, and around 75% of the owls reacted to those warnings.

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Essentially, squirrels are acting as an early warning system for other species.

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So this creates a huge ecological dilemma. The poisons meant to solve the squirrel population can end up harming endangered predators directly, while also disrupting ecosystems indirectly by removing a keystone species.

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And this really shows why the war on squirrels has become so complicated. Once you interfere with one species, the effects rarely stay isolated to just that one animal.

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After more than a century of fighting, why hasn't the war been won?

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The answer seems pretty simple. If squirrels have access to enough food, they will find a way to survive.

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California ground squirrels are incredibly adaptable. They learn new ways to burrow, repopulate quickly, and adjust to changing environments. So most eradication strategies only solve the immediate problem by killing current squirrels while the surviving population eventually rebounds.

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Which means methods like mass killing campaigns, trapping, gassing, or baiting may reduce populations temporarily, but don't really address the larger ecological concerns allowing squirrels to thrive in the first place.

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And because of that, some researchers have started proposing entirely different solutions. A study prepared by the San Diego Zoo Institute for Conservation Research looked at the risk California grasslands face from grazing, agriculture, and housing development, actually identifying California ground squirrels as a necessary keystone species.

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The researchers proposed translocation, basically relocating the squirrels instead of exterminating them.

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Now, obviously, relocating thousands of squirrels comes with logistical problems. Capturing them and finding safe habitats isn't easy. But it raises a bigger question. If squirrels are both destructive pests and important ecological contributors, should the goal really be eradication at all?

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Because ultimately, the war on squirrels isn't really a story about squirrels being inherently evil or destructive. It's about what happens when animal behavior starts conflicting with human priorities.

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California ground squirrels didn't become labeled as pests because they were unnatural to the region. They became pests because their lifestyle interfered with agriculture, urban development, and human economic interests.

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And our research suggests that targeted extermination alone probably isn't a long-term solution. More sustainable approaches may involve public education on feeding wildlife, understanding squirrels as a keystone species, and exploring alternatives like relocation.

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In the end, the war on squirrels tells us so much more about ourselves than it does about squirrels.

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Every weapon, every strategy, and every policy reflected a human decision about what was worth defending. Crops, cities, public health, animal life, or the idea of control itself.

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And maybe that is why this conflict has lasted for more than a century. The battle was never simply about defeating squirrels. It was about deciding what kind of relationship humans wanted with the natural world they kept turning into a battlefield.