[MUSIC] 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.