Why are cockroaches so hard to kill? - Ameya Gondhalekar

In the Egyptian Book of the Dead, there’s a banishment spell that declares,

“Be far from me, O vile cockroach.”

More than 3,000 years later, we’re still trying to oust these insects.

But from poison traps to hastily brandished slippers,

cockroaches seem to weather just about everything we throw at them.

So what makes cockroaches so hard to kill?

There are nearly 5,000 cockroach species.

99% of them live in a range of habitats where they play important ecological roles

by recycling dead or decaying organic matter

and nourishing other animals.

But a couple dozen species adapted to live in close association with humans.

German and American cockroaches are among the most common.

And they owe their resilience to a combination

of physical and chemical adaptations.

When it comes to old-fashioned removal methods,

they're troublingly tenacious.

An American cockroach’s sensory hairs or structures pick up subtle air currents

and rapidly send signals to its central nervous system.

The roach can then turn and sprint away within a few milliseconds.

And it’s among the fastest invertebrates ever recorded,

reaching speeds of up to 50 body lengths per second.

This would be the human equivalent of running more than 300 kilometers per hour.

And finding a hiding place is no problem.

With its flattened, flexible body,

an American cockroach can squeeze into spaces less than a quarter of its height.

Even if we do land a hit, it can withstand compressive forces

of up to 900 times its own weight by distributing the impact along its body.

And the cockroach’s toughness doesn’t end there.

Cockroaches can eat a variety of organic matter,

including hair, dead skin, adhesives, and paper.

This is made possible by an expansive set of digestive enzymes.

Cockroaches are able to thrive even in nutrient-poor environments.

Roaches often eat decaying foods that are low in nitrogen—

an essential component of DNA and proteins.

But they survive by storing nitrogen-containing wastes in their bodies

and having a resident group of bacteria recycle the nitrogen

into useful molecules for them.

Meanwhile, German cockroaches will eat their own poop, vomit,

and dead or dying colony members without hesitation.

An American cockroach will frolic in sewers,

consuming excrement and toting microbes like Staphylococcus aureus and E.coli.

But they’ll rarely suffer any consequences.

This is because they’re equipped with genes that provide immunity

against numerous pathogens.

These genes are often duplicated many times over.

So when infected, the cockroach’s immune system efficiently unleashes

many antimicrobial molecules.

Cockroaches also have a slew of defenses against pesticides.

When a non-resistant roach walks on a surface that’s been sprayed

with a pyrethroid insecticide, for example,

the results will likely be fatal.

Once absorbed, the chemical binds to sodium channel proteins,

which help propagate nerve impulses.

The pyrethroid keeps the sodium channels open,

so the nerves fire repeatedly.

And soon, the cockroach dies.

But if a resistant roach is exposed to pyrethroids, it’ll be just fine.

Genetic mutations have given them sodium channels

that the pyrethroids can’t bind to.

The cockroach also produces more detoxification enzymes,

which render the pesticide harmless,

and the cockroach simply excretes it as a waste.

Because German cockroaches reproduce especially quickly,

populations may evolve resistance to a new pesticide within months.

So far, they're already resistant to 43 different chemicals.

But contrary to popular belief,

cockroaches would probably not survive a nuclear apocalypse.

Compared with other insects,

cockroaches are only mildly tolerant to radiation.

They would die near the sites of nuclear explosions

and would still be severely compromised miles away.

Moreover, disasters that threaten humanity

also jeopardize the habitats and buffets we provide roaches.

Perhaps the only way to beat them is through our mutual destruction.

Or maybe cockroaches would find even more surprising ways to thrive

long after we’re gone.