How has COVID-19 impacted rat populations worldwide?

COVID-19 has changed behavior on a global level. We've all found ourselves experiencing the world in a very different way than we're used to. Everything from going to the store to riding public transit has changed. However, it's not just people who've had to adapt to a rapidly changing world. Animals that live in close proximity to humans have seen their environments change as well — especially those that live almost entirely within a human-built ecosystem. 

The worldwide rat population has been particularly impacted by COVID-19. As the world's largest populated cities isolated in quarantine, rats were separated from their largest source of food, our waste! Here, we take a look at how COVID-19 has influenced rat populations worldwide.  

COVID-19 and rats 

When people think of pandemics, it usually doesn't take long until the bubonic plague comes up. In the mid-1300s the bacterial infection also known as The Black Death spread all over Europe. Much later on, humanity would discover that rats and mice were major carriers of the plague through parasitic fleas that were carried across the continent. This has led many people to wonder if rats could spread COVID-19 at the beginning of the pandemic. The news of COVID-19 showing up in mink has furthered that concern. Can a rat catch COVID, or spread it as an asymptomatic carrier? 

Thankfully, although it isn't 100% conclusive, it doesn't seem like rats can catch or spread COVID-19. Minks are a distant enough relative of rats to have a very different immune system so humans don't need to worry about catching COVID-19 from a rat, at least as far as we can tell. Rat populations haven't been directly infected by COVID-19, but have been impacted by humanity's changing behavior during the pandemic.

Changes in our food consumption

Most of us have had to change our relationship with food during the pandemic. Sometimes this has been a major issue. For example, stores ran out of a lot of staple items in the early days of COVID-19. Even the raw ingredients for various meals began to thin out as people who hadn't cooked in ages started to get back into the habit. Restaurants, in particular, needed to make some big changes to their operations. 

Many restaurants closed down indoor dining for most of the pandemic. As things opened up again, outdoor dining became possible. But outdoor dining was resumed in much lower numbers than was previously seen. However, even then people were eating at home more often than ever. Most of the public also stopped eating while just walking around in the city or waiting for public transit. There was just a lot less food being eaten outdoors in the average city, and this wasn't just within a single country. It happened as a worldwide trend almost everywhere on earth. 

Most of us experienced this as a mild inconvenience. Nobody liked having our continual access to food disrupted, but at the same time we had food in the fridge, and takeout or delivery was always an option. Think about how this would impact rat populations. A rat can grow to maturity in about three months. 

Imagine how many rat generations would go by in the proximity of a restaurant that had been around for a decade. A rat colony might have been eating table scraps or dumpster residuals from the same restaurant for an untold number of generations, and then with the arrival of COVID-19 their food supply would disappear in the blink of an eye. This has led to a number of changes among the urban rodent population.

Home is where the food is

A rat usually tries to live fairly close to their food supply. Until recently, this was a fairly simple prospect. A rat in an urban environment, or even suburban, would typically be able to find areas where humans left food just sitting around. A typical restaurant will continually fill up dumpsters with edible garbage. What's more, people eating outside or finishing up takeout will usually add additional food into the environment. 

COVID-19 changed that entire dynamic for people and urban rats alike. The constant supply of food for rodent populations disappeared almost overnight. This created a mass migration for rats and mice who looked to other places for food sources.

This is one of the biggest reasons why so many people have found rodents in their houses over the past year. Rat colonies that have lived near humans for countless generations aren't simply going to head back into nature. They're going to look for the type of environment they're most used to. And for most rat and mouse populations that means finding different humans to live with. The only problem is that rats interact with households in very different ways than they would a restaurant. 

A rat who lives near a restaurant has an almost never-ending supply of food to choose from. They're often able to sample from the leftovers of hundreds, or even thousands of people, on any given day, but a rat driven to people's homes will have to make due with leftovers from far fewer people. Giant crowds can sustain multiple rodent colonies, but even an entire family of humans might not create enough attainable food waste to feed a rat colony. 

Food scarcity and rat behavior 

A rat who's been forced to migrate from their home is under a lot of stress. These aren't the same types of rodents who live in forests or plains. An urban rat is as used to creature comforts as we are and very few of us would be ready to migrate in search of food. 

A rat who's had to go from a comfy nest near restaurants to a human's home is typically in a rough state. They're hungry, stressed, and probably more than a little desperate. But on top of this, they're also facing a lot of competition from other rat or mouse colonies. 

Both individual rodents and colonies have become considerably more aggressive due to the COVID-19 related food shortages. About the only thing worse than finding a rat in your box of cereal is finding an angry rat, but that's exactly what's happening as rats head out in search of new homes and new food sources. 

It's difficult to fully comprehend just what effect COVID-19 has had on the average city rat. New York City, for example, has an estimated rat population of around 2 million, and we could find about 27,000 restaurants there in 2019. Now imagine how 2 million animals would fare when that food supply chain broke down. 

We find many reports of rats even getting desperate enough to turn on each other. Some rodents have resorted to cannibalism. Others have turned to infanticide. Some cities have even seen swarms of rodents traveling together in a desperate search for food. 

A worldwide problem 

One of the most worrisome aspects of this rat problem is the sheer scope of it. We can find rat populations in every continent other than Antarctica. At the same time, COVID-19 has had a major impact on every country in the world. The examples of rat migration and aggression aren't limited to any one geographic area. 

Every part of the world that has experienced issues with COVID-related restaurant closings has also experienced these rodent issues to some degree. People are also understandably concerned with how they can deal with it. Individuals who've never even seen a rat before have found themselves needing to deal with them for the first time.