December 2018^ DISCOVER^53By 1854, the insect was in New York
City. It now lives from Alaska to
Antarctica, having moved with peoples
of nearly every nation in their boats,
cars and planes. It is surprising the
roaches aren’t yet on the International
Space Station.
IF IT DOESN’T KILL YOU...
Certain conditions are needed for
animals to adapt quickly to pesticides:
the targeted species must be genetically
diverse (or borrow new genes from
other species), the chemical kill almost
all of the targeted species, the chemical
exposure happens repeatedly, and the
targeted species’ competitors (parasites
and pathogens) be missing.
Cockroaches meet these condi-
tions, but so do nearly all the other
pests we target. Besides roaches, bed
bugs, head lice, houseies, mosqui-
toes and other common insects in
our houses have developed resistance
to our pesticides.
If a species becomes resistant to a
pesticide or other means of popu-
lation control, that species can
readily move to another home
that uses the same control
measure. In rural environ-
ments, the spread of resistant
species might be slow. But in cities,
it can happen rapidly because apart-
ments and houses are closer together.
Even though human social networks
often fall apart in cities, with people
feeling lonely and isolated, the resistant
pests stay connected. Their network is
a kind of river of our own making,
and it ows through our windows and
under our doors.
Although resistance is quick to
evolve among the pests, it is less likely
to evolve in species we don’t target.
This is doubly problematic. The irst
problem is the simple loss of the bio-
diversity around us, on which wild
ecosystems depend. A recent study
found that over the last 30 years, the
biomass of insects in Germany had
declined in wild forests by 70 percent.
The jury is still out on the cause, but
many scientists believe a likely one is
pesticides. The second problem is that
among the species killed by pesticides
are those that beneit us, including the
natural enemies of the pests we are
trying to control.ALONG CAME A SPIDER
Whether you like it or not, spiders are
great at pest control. If you kill them
in your home — and this is precisely
what we do with many kinds of pesti-
cide applications — you do so at your
own expense.
As children, we learned about the
old woman who swallowed a spider
after swallowing a y. That case didn’t
turn out well. (Spoiler alert: She died.)
Others have turned out better.In the late 1950s, J.J. Steyn, a
researcher in South Africa, was trying
to igure out how to control houseies
(Musca domestica), longtime associ-
ates of humans. Houseies have spread
around the world to nearly every
region we inhabit. They can be a real
problem, especially when sanitation is
poor. Houseies carry more pathogens
than cockroaches, including many
that cause diarrhea and are associated
with more than 500,000 deaths a year.
Houseies also evolve rapidly. By 1959,
those in South Africa were resistant to
at least 15 major pesticides.
Although the ies are largely invinci-
ble to chemistry, they are not invincible
to spiders.