There’s nothing like walking through cool grass on a warm summer's day.
But every Southerner knows that a barefoot stroll in the yard comes with risks…
"Ow, ow! OW!"
This fire ant mound should be a familiar sight to anybody who lives in the southern U.S.
But you won’t see them marching around in little lines on the ground. We're surrounded by an
underground network of foraging tunnels, but this is home base. And the best way to get
to know what’s inside is to give it a poke.
A fire ant’s main senses are touch and smell. The slightest disturbance and workers release
alarm pheromones, a chemical signal that can raise the entire mound to defense within seconds.
Anything sitting still is now a target, so let's get out of here.
A fire ant’s bite isn’t what hurts. Their mouths only serve as anchors so they can curl
around a sharp stinger and inject a dose of venom, a painful reminder they’re in the
same order of insects as bees and wasps: the Hymenoptera.
Insect researcher Justin O. Schmidt developed a pain index for Hymenoptera venom, mostly
by allowing himself to be stung over and over. The tiny sweat bee, for instance, is a 1…
“a tiny spark singeing a single hair”. The bullet ant scores a 4, the most painful
grade, like “fire-walking over flaming charcoal with a 3-inch rusty nail in your heel.”
Fire ants score a mere 1.2 on the Schmidt Pain Index, but they tend to sting multiple
times, like this one did. It's already starting a local immune response around that venom:
it's red, it's itchy, it's burning. It does not feel good. Within a few days the cells
will actually die and leave me with a nice little white bump that I will not be able
to resist popping. The things I do for this show.
These stings have made fire ants a target of pure, unadulterated hate in the southern
U.S., but it’s important to remember that just like us, these ants are an imported species.
The red imported fire ant, arrived in the U.S. between 1933 and 1942, accidentally scooped
from their home in South America, placed onboard a ship, and dropped in Mobile, Alabama.
They left behind a hard life full of daily ant warfare, but in Alabama they found opportunity,
few enemies, and a boy named Edward Wilson. E.O. Wilson would later become the world’s
leading expert in ant biology, but as a teenage scientist in Mobile, he recorded the first
known sighting of imported fire ants. Over the next two decades, as Wilson and other
scientists watched these ants spread out from Alabama, southern farmers went into full freak
out.
[DRAMATIC MUSIC]
Now, maybe it was because the nation still had war on the mind, or the ants had “red”
in their name, but the US stopped at nothing to eradicate them. Retired World War II bombers
took to the air loaded with pesticide, indiscriminately showering the South with millions of tons
of poison.
We’d later learn that the pesticides used were many times more toxic than DDT.
E.O. Wilson called the bombing campaign the “Vietnam of entomology” and it was one
of the inspirations for Rachel Carson’s “Silent Spring.” In the end, aerial pesticides
did do a lot of killing, but instead of fire ants, it was mostly to livestock, birds, fish,
and native ant species.
Nature hates a vacuum. By wiping out the native ants, we made it easier for imported fire
ants to advance. They’ve since spread from Florida to Texas… on to California, even
to Mexico, China, and Australia. Solenopsis invicta seems perfectly evolved for invasion.
Part of the answer lies in their how they reproduce. Hordes of winged males and future
queens take to the air in massive mating flights. Pregnant queens then air-drop into new open
territory free of competition, break off their wings, and bury themselves to give birth to
new colonies.
In many places, like here Texas, a genetic variation has made some fire ants lose their
territorial nature. Many colonies here are home to many queens, they’re more densely
packed than their territorial relatives, allowing them to spread like a creeping fungus instead
of airborne seeds.
Thanks to their tropical origins, during floods, entire fire ant colonies can clump together
and float until they find a new home. They invade by land, air, and water.
It’s no coincidence fire ants and humans are constantly running into each other. Fire
ants crave disturbance, and humans provide that everywhere we go. Think of it this way:
If you clear an area, take away the natural vegetation, the first thing to move back in
are weeds, and so it is with fire ants: Tiny animal weeds.
Like weeds, they're more annoying than dangerous, but imported fire ants cost $6 billion every
year, damaging everything from golf courses to electrical equipment, where they sometimes
nest. Eradication is impossible, but the answer to controlling them might come from their
South American home.
Tiny buzzing insects, barely visible to the naked eye.
Ant-decapitating flies. Phorid flies - that’s their technical name
- are one of invicta’s natural enemies back home.
They hover over unsuspecting workers, zip down, lay an egg inside the ant, and fly away.
That egg hatches, a maggot crawls into the ant’s head, eats everything inside, and
eventually the ant’s head falls off. Scientists have imported these flies into
the U.S. so they can be used as a biological control method. One fly can terrorize hundreds
of ants, putting a whole colony on the defensive. These flies are super-specific to the species
they attack, so scientists don’t think they’ll become a threat to native ants.
But even if phorid fly control works perfectly, imported fire ants will remain permanent residents.
The name “invicta” means “unconquered” after all.
Just like the people who accidentally brought them here, these ants found themselves in
a strange land of opportunity, just trying to make the best of it. The bright side is
that after decades of studying how to kill ‘em, the fire ant now rivals the honeybee
as the best understood of all social insects. And for all their stinging, they've taught
us a ton about evolution, social behavior, and of course parasites that make your head
fall off.
Karl von Frisch said something about those honeybees that I think applies equally well
to fire ants: They’re “…like a magic well, the more
you draw from it, the more there is to draw.”
Who knows, each time we walk barefoot through their little world, maybe they’ve just been
begging to be noticed. Stay curious.