Earth's ecosystems have always been changing,
with species mixing and mingling thanks to migrations, freak events, and slow creeping
expansions. But since we humans arrived on the scene, we've put things into fast-forward,
moving plants, animals, and other organisms around the globe -- whether intentionally
or not. Once in a while, one of these transplants
might have an evolutionary quirk -- like deadly poison, a lack of predators, or a voracious
appetite -- that unexpectedly helps it dominate its new territory. Earthworms, for example,
were introduced into North America by European settlers and have been inching across the continent
ever since - tilling soil and improving crop yields as they go. But if a newcomer starts to harm us or a part
of the environment we care about, we'll call it an "invasive species." Technically-speaking,
humans aren't "invasive," because we don't usually consider ourselves an ecological threat
to... ourselves. But other species certainly are. One way they
get our attention is by costing us money. A lot of money. The US spends billions of
dollars fighting invasive weeds like the pretty but pesky yellow rocket flower that chokes
fields and creeps onto golf courses and lawns. Other invaders wreak so much havoc on fragile
ecosystems that we can't help but notice even if billions aren't at stake. For example,
the yellow crazy ant - a likely native of Southeast Asia - has been eating many beloved
and endangered Australian creatures since its arrival several decades ago. These little
ants feast on nearly anything and everything in their path - insects, amphibians, birds,
small mammals, even the famous red crabs on Australia's Christmas Island, which used to
keep the island's undergrowth in check; without them, the ecosystem has veered into chaos. But noticing invasive species is easy - dealing
with them is the real challenge. When we brought rabbits to New Zealand for
food and fur, they escaped and bred like...well...rabbits, overrunning the country. So we introduced
ferrets to control the rabbits; but they too spread like wildfire, generally ignoring the
rabbits while gobbling up rare species like the now nearly-extinct kakapo. New Zealand
is still overrun by both furry fiends, and this is just one of many well-meaning attempts
at biological control that have ended in disaster. The best way to fight an invasion is to first
arm ourselves with knowledge: Instead of trying to kill Australia's yellow crazy ants by just
spraying insecticide everywhere, we've learned that the best approach is a year-long multi-step
assault that specifically targets ant-riddled areas at the times when the egg-laying queens
are mature and susceptible to our treatments. Then we spread two kinds of bait for the workers
to bring back to the nest - one kills, and the other sterilizes the queens. Neither poison
is perfect, but executed together, they can knock out a whopping 99 percent of the population. But with many invasives, even 99% isn't enough,
because it doesn't remove whatever advantage gave the invaders an edge in the first place.
So unless we honest-to-goodness get rid of every reproductively active individual, eventually
they'll return as vigorously as before, keeping us constantly on our toes. We really just need to stop moving potential
troublemakers around in the first place, leaving bunnies where they belong and making sure
ants and earthworms don't stow away in ships, cars, or excavators. But in a modern, globalized
world, this is easier said than done. For those species that we do accidentally (or
intentionally) let loose only to see them spread wildly out of control, our best hope
is to learn as much as we can about their habits and their biology - only then do we
have a chance of keeping their harmful "ant"-ics at bay.
