The Great Mouse Invasion

In 1920s California, a plague of Biblical proportions

January 19, 2025

Slipping on ice in your car is a moment of panic. The death grip on the wheel, and the feeling of betrayal, that fragile ice could potentially cause so much destruction.

But once, in Kern County, California, the slickness of the road wasn’t ice. It wasn’t water or mud.

It was dead mice.

A pile of scurrying brown mice

In my book (obligatory plug for my book) I write about when mice (or other rodents) erupt into “plague” proportions, basically a Biblical amount of rodents suddenly on the landscape. Australia has a long and storied history of rodent plagues, both invasive house mice and native species, as well as rabbits. Other countries have also seen similar outbreaks.

The climate of Australia plays a role in why they get mouse plagues (though no one can truly predict when the next will arrive). They have dry periods, and wet ones, and wet ones often lead to bumper crops of cereals. Mice love cereals as much as people do, and begin to reproduce in large numbers. The suddenness is terrifying, but not surprising, when you realize that a mouse can go from birth to teen mom in a mere three weeks, and each litter can produce between four and 12 pups. The mom can then get pregnant again—while weaning her first litter. Two mice can become 12, then 144, then…you get the idea. Those mice need to eat, and when they can’t find food in their usual haunts they will scurry to where they can. Through the fields, in the walls, on the floor.

The first reports from Australia came through in 1871, but mouse plagues continue today. In fact there was a large plague of mice northwest of Sydney in 2021. It was so bad it caused a complete evacuation of a prison due to safety concerns, and people were catching hundreds of mice every night. People were attacked by mice in their hospital beds. In 2021.

It will happen again. No one knows when, but it will.

Mouse plague is born.

North America doesn’t usually seem to have the conditions conducive to mouse plague—unless it does. And in Kern County, the invasion of the house mouse created just the right conditions.

The house mouse, according to local report, had only arrived in the area about 50 years before. Prior to that, Kern County boasted a population of voles, deer mice, kangaroo rats, and pocket mice. But Mus musculus, the house mouse, is not a neighbor to be trifled with.

It’s November, 1926. And there are mice everywhere.

The location is Buena Vista Lake, which was then a dry lakebed that was sometimes inundated by the Kern River (there’s a permanent lake there now, it’s a man-made reservoir). At the time, it was merely a well-watered area that was farmed with grains and cotton. In those fields, mice thrived, purportedly in the millions. A few native rodents clung on, but they were being outcompeted by the voracious house mouse.

After the harvest (and subsequent sheep grazing), ground cover was low. Then, apparently, it rained. The lakebed filled. And the mice had to leave. They headed for Taft, a nearby town of just over 3,000 people.

The mice coated the town. In houses, walls, beds. They coursed in rivers down the streets, where passing wagons and early cars squished the hordes, causing “. . .highway[s] plastered with dead mice, and millions of them alive chasing across the highway. . .”

The Bureau of Biological Survey, usually tasked with “pest” control in the form of poisoning coyotes, was mobilized in January of 1927. They sent a guy named Stanley Piper (yes, really, rodent plague, dude named Piper, I’m sure he NEVER lived it down). Piper and a crew of 25 deployed 36,000 kg of alfalfa—laced with strychnine, the poison method of choice at the time for mice and coyotes alike.

Thanks for reading Team Trash: Where People and Wildlife Meet! This post is public so feel free to share it.

Who dunnit?

They declared victory in early Feburary. But ecologists (and probably townspeople) were left with questions. Why did this happen? Why was there a plague of mice o’er the land?

One detail stuck out. There was a sudden influx of predatory birds, no doubt drawn to the honestly horrifying smell that millions of mice make. But interestingly, there were no LAND predators to feast on the buffet. And it’s thanks to the town’s above-mentioned savior, the Bureau of Biological Survey, the precursor to what would become Fish and Wildlife.

Ecological management was just coming into being, and it was not about preserving ecosystems per se. Instead, it was focused on creating more of what humans wanted, and what humans wanted was easy hunting. That meant no predator competition, thank you. Anything that could come for the animals we wanted needed to be put in its place and its place was extinct.

This might sound like an utterly ridiculous view, but at the time, it was pretty widely accepted. There weren’t strong ideas of food webs, or of interconnectedness of ecosystem functions. A pastoral, beautiful landscape was one without predators in it, one with a world of prey where humans were the only hunter.

In Kern County, this took the form of the Bureau of Biological Survey conducting a campaign to eliminate predators, particularly coyotes, from the area at the request of the local sheep farmers. While landowners had been poisoning and shooting predators for about 20 years prior, in 1924 and 1925, the government set out poisoned baits, killing off coyotes, but also foxes and skunks.

Mice might seem like a rather small snack for coyotes, but rodents actually make up a significant part of a coyote’s diet (ok to be fair, everything makes up a significant part of a coyote’s diet). Foxes also eat rodents, skunks won’t turn them down.

So for a long time there was speculation that this lack of predators was what allowed the mice to get out of hand, and that this plague of mice was the ecosystem’s punishment. Was this the case? Was it the lack of predators (an idea that seems very logical in this day and age)? Or was it just that mice breed like mice?

I love so much that a paper in 2007 set out to address this question. Seong-Hee Kim et al. modeled the populations of mice, predators, and plants over the period from 1890 (when the house mouse arrived) over the mouse plague and all the way up to 1973. They tested models of native mice, predators, and no invasives, and compared them to invasive mice and predators or invasive mice and no predators. Because not only did the house mouse cause this plague, they also drove all native rodents to the brink of extinction.

And it turns out? The mouse eruption would have happened, come hell or high water. With or without predators being removed. Predators probably could have brought the peak of the plague down a bit…but the highways would still have been coated in mice. The rodents had entered a boom and bust population cycle, where they reproduced like mad when times were good, and died off like mad when they weren’t.

In this case, the conditions were right, the crops were good, and there was nowhere else for mice to go. But if predators had stayed, the paper argues, the invasive mouse might not have killed off all other small native rodents in the process.

In the end, they conclude, it was that amazing, shocking, overwhelming reproductive power of mice that caused the plague. Never underestimate mice. And next time the road is slick…well just thank your lucky stars it is what it is.

References:

Where have you been? (links to read)

There are bodies that America believes should not be unhindered. Black and brown bodies; gender nonconforming bodies; bodies with uteruses.

The news is filled with anger at these bodies unhindered in our country — crossing borders, getting abortions, walking down the street, existing outside gendered conformity. These bodies laughing. These bodies taking time to run or take the path through the woods to the park. These bodies in the middle of the work day, running, hopping over cracked sidewalks and stepping over potholes. It’s a freedom our neighbors begrudge us, peering out the windows, posting on social media when they see us.

  • “Have you heard of this thing called the “equator” and these other two things called “hemispheres”? Don’t you know half the world is experiencing summer right now? It just feels very self-centered to be talking about loving wintertime when there are billions of people who aren’t even experiencing it right now.” McSweeney’s, perfectly capturing the essence of being a writer on the internet in 2025.

  • How many species take the phrase “eat shit” literally? More than 150, it turns out! Coprophagy, the eating of poo, is quite popular across the animal kingdom!

  • There’s a perception out there that men don’t read. Is it true? And if it is, what does it mean? I’ve got my own thoughts here.

  • COVID hit 5 years ago. We’re trying our hardest to pretend it never happened, even has it still kills people. I recall personally when the pandemic first started, everyone wondered why no one seemed to really talk about or think about the 1918 flu. Now? Now I think I know.

Where have I been? (things I wrote!)

First, if you’re here from TikTok, hello! This is….probably not what you were expecting, was it? If you’d like Insomniac Anatomy Academy served on a platter, please start here, and also here!

For those NOT on TikTok, for the past year or so I’ve been studying anatomy when I can’t sleep (I have insomnia. Yes, I am in treatment for it. Yes, I do sleep 4-6 hours per night this a problem with sleep latency). I started going on Bluesky, and then on TikTok and Instagram, to share the fun and funny facts I learned about the human body. And in the past month or so…people started to notice. Unfortunately, the TikTok app is, as of this moment, leaving. But I will continue making the videos. I will post them on Insta, FB, Youtube, and Bluesky. And yes. I am well aware that all of these are problematic. The only unproblematic app is one that merely isn’t problematic YET. You are, after all reading this on Substack. But I want to write, and share, and help people learn. That means going where people are.