8 Unexpected Cockroach Facts

Some roaches have individual personalities and democratic tendencies

The German cockroach
ErikKarits / Getty Images

Few creatures are as unpopular with people as cockroaches. We not only recoil at the sight of them, but often go out of our way to eradicate them, or at least reflexively kill any we see.

But most of us know a lot less about roaches than we think. They are surprisingly diverse, including many species that have no desire to share our homes with us. And even among the few cockroaches that do infiltrate human dwellings, there are some noteworthy quirks that could challenge our typically one-dimensional view of these wily scavengers.

Here are a few facts you may not know about cockroaches.

1. Most Roaches Are Not Pests

Single Madagascar Hissing Cockroach known also as Hisser in an zoological garden terrarium
Bernard Bialorucki / Getty Images

More than 4,000 cockroach species are known to science, and most of them just aren’t that into us. The vast majority of cockroaches ply wild habitats — rottings logs in deep forests, for example, or damp burrows on cave floors. Of those several thousand species, only about 30 are considered potential pests.

Of course, at least some of these 30 species have made outsized impressions on humanity. The German cockroach, in particular, is "the cockroach of concern, the species that gives all other cockroaches a bad name," according to the University of Florida Institute of Food and Agricultural Science (IFAS). Other major species of concern include the American, Australian, brown-banded, and Oriental cockroaches, all of which are now cosmopolitan pests.

Our disgust for cockroaches may be disproportionate to the danger — especially for non-venomous, non-bloodsucking insects that flee when confronted — but it isn’t baseless. Aside from their aesthetic shortcomings, pest cockroaches can pose a sanitary hazard around food supplies, especially in large numbers, and they can trigger asthma and allergic reactions in some people. According to the World Health Organization (WHO), cockroaches “are not usually the most important cause of a disease,” but like house flies, they could play a supplementary role in spreading some pathogens. Cockroaches also may cause significant psychological stress, the IFAS notes, both due to fear of the insects themselves as well as the social stigma associated with roaches.

2. They Have Seniority

The earliest human species known to science lived roughly 7 million years ago. Cockroaches, by comparison, had reached their modern form by the Jurassic Period, about 200 million years ago, and primitive roaches were around even before dinosaurs, during the Carboniferous Period, some 350 million years ago. It may not help when you see one scurrying across the kitchen floor late at night, but it’s at least worth noting roaches were here first.

3. They Have Personalities

German cockroach

OZGUR KEREM BULUR / Getty Images

A personality, as the term suggests, was once thought to be unique to people. However, we now know lots of other animals also have individual personalities, and not just our fellow vertebrates. Jumping spiders, for example, have been shown to exhibit varying levels of boldness or shyness, exploration or avoidance, and sociability or aggression, a set of individual behavioral signatures that scientists refer to as “personality types.”

Research suggests some insects have personalities, too, including cockroaches. In a 2015 study published in the Proceedings of the Royal Society B, researchers found that some American cockroaches tend to be “bold” or “explorers,” while others are more “shy or cautious,” and these individual differences can help influence the broader dynamic of their social group.

Lots of like-minded cockroaches are better at quickly choosing a shelter site together, the researchers found, which can offer an advantage in some situations. In a natural setting, however, not all shelters have the same quality, so choosing a good shelter may be as important as choosing one fast. "[G]roups characterized by a large distribution of personalities could be the best trade-off between speed and accuracy,” the researchers wrote.

4. They Embrace Democracy

Roaches are social insects, but unlike many social ants and bees, they don’t live in colonies ruled by a queen. Instead, they often form more egalitarian and democratic aggregations, in which all adults can reproduce and contribute to group decisions.

In fact, cockroaches offer one example of democracy in the animal kingdom, at least based on the way they collectively choose shelters. In a study of German cockroaches, for instance, researchers found that a group of 50 insects naturally divided themselves into appropriate subpopulations based on available shelters, but reorganized when conditions changed, helping them strike a flexible balance between cooperation and competition.

5. They Can Be Trained

More than a century after Russian physiologist Ivan Pavlov famously demonstrated classical conditioning in dogs, researchers from Japan revealed a similar response in cockroaches. Hidehiro Watanabe and Makoto Mizunami, of Tohoku University, first showed that American cockroaches salivated in response to sucrose solution, and not to vanilla or peppermint odors. But after differential conditioning trials — in which each odor was presented with and without sucrose — the sucrose-associated odors induced the roaches to salivate, a conditioning effect that lasted for one day. This was the first evidence of salivation induced by classical conditioning in any species other than dogs and humans, the researchers noted.

Other research has since supported the findings. A study published in Frontiers in Psychology in 2020, for example, found that cockroaches show individuality in learning and memory during both classical and operant conditioning. “Our results confirm individual learning abilities in classical conditioning of cockroaches that was reported for honeybees and vertebrates,” the researchers wrote, “but contrast long-standing reports on stochastic learning behavior in fruit flies. In our experiments, most learners expressed a correct behavior after only a single learning trial, showing a consistent high performance during training and test.”

6. They’ve Helped Inspire Robots

Cockroaches are notoriously fast, both in terms of reaction time and top speed. They’re also known for squeezing through tight spaces and defying our attempts to crush them. They can run as fast through a quarter-inch gap as they can through a half-inch gap by reorienting their legs out to the side, according to researchers at the University of California-Berkeley, and can withstand forces 900 times their own body weight without injury. These may not be good qualities in a pest, but they all make intriguing possibilities for a robot.

In 2016, the team of Berkely scientists unveiled a robot that imitates cockroaches’ ability to rapidly squeeze through small spaces, which could be useful for search-and-rescue missions.

And in 2019, another team published a study describing a different roach-like robot, which borrows a few key attributes from its insect inspiration. The tiny robot can run at 20 body lengths per second, similar to the speed of a real roach and reportedly among the fastest of any insect-sized robot. It weighs just a tenth of a gram, yet can withstand a weight of around 60 kilograms (132 pounds) — about the weight of an average adult human, and roughly 1 million times the weight of the robot itself.

7. Some Cockroaches Are Endangered

Despite the obvious abundance of many pest cockroaches, a few wild cockroach species are suffering the opposite fate. The Lord Howe wood-feeding cockroach, for one, is classified as an endangered species in New South Wales, Australia, where it exists only on the Lord Howe Island group. Now extinct on the main island — due to threats including habitat loss and predation by invasive rodents — the only survivors now live on smaller offshore islands.

Two other species of cockroaches are also listed by the International Union for Conservation of Nature (IUCN) as under threat, both of which inhabit the island nation of Seychelles, in East Africa. The IUCN lists Gerlach's cockroach as Endangered, while the Desroches cockroach is classified as Critically Endangered. Both species have a limited natural range, and face threats from forest loss due to human development, as well as rising sea levels due to climate change.

8. Pest Cockroaches Are Outmaneuvering Us

The cockroach crawled to the bait in the form of pills and fall into the trap of sticking to the sticky surface.
Dmitriydanilov / Getty Images

While most cockroach species don’t share space with us, the few that do have followed us around the world for millennia, adapting to almost any habitat we’ve established. Some are now rarely found away from human structures, sometimes even specializing in different parts of a home — like the “furniture cockroach,” often found away from food-containing areas, or the American cockroach, whose genome seems well-suited for feeding on human garbage.

Cockroaches have proven eerily adaptable in both physiology and behavior, helping them resist some of our few effective means of managing their populations. They are rapidly evolving resistance to multiple types of insecticides, according to a study published in Scientific Reports in 2019. Researchers subjected German cockroaches to three kinds of insecticides in various ways — one at a time, alternating, or all together — but most roach populations didn’t decline in any scenario. This suggests the roaches are quickly evolving resistance to all three chemicals, the researchers noted, and that cross-resistance to pesticides represents a “significant, previously unrealized challenge.”

In another study of German cockroaches, researchers examined how some populations may have rapidly evolved an adaptive behavioral aversion to glucose, which is commonly used in poisoned sugar baits. Roaches usually love glucose, but evolutionary pressure from roach traps may be encouraging a genetic aversion in some populations. The researchers showed the neural mechanism behind this aversion, which suggests glucose might taste bitter to these roaches, who still enjoy other sugars like fructose.

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