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.
