around 48 million years ago in a warm subtropical forest in what's now germany
zombies were on the march these zombies were ants and their bodies and behavior were no longer under
their control they had become infected with the spores of a fungus that was now growing inside
them this fungus was actually manipulating their movements forcing them to do something
they'd never ordinarily do something strange and specific the ants abandoned their colony
climbed up a nearby plant onto the underside of one of its sleeves and bit down hard on
the leaves veins locking themselves into place this behavior is known as the death grip and as
the name suggests it's the last thing these ants would ever do soon the fungus sprouted probably
from their heads releasing spores to infect new hosts and continue the cycle all that
was left behind were the marks on that ancient leaf it fossilized and was published in 2011
complete with a distinctive death grip scars this single fossil leaf is the oldest known evidence of
zombified ants which still exist today modern zombie ants even perform the exact same death
grip behavior something healthy ants never do so we know that this creepy capability to
manipulate behavior is ancient but how and why did it come to exist in the first place well it turns
out the fungus's ability to turn ants into the walking dead may have evolved as a response to
the development of an equally complex behavior of the ants themselves a thing called social immunity
over hundreds of millions of years many fungi have become specialized for infecting insects
and other arthropods generally it happens like this a fungal spore will attach to a host
penetrate its exoskeleton and start growing within its body eventually when the fungus is ready it
erupts from the host and releases spores to find and infect new victims and if you're an old-school
sci-fi fan like i am then i know exactly what you're thinking and you are right these fungi
are basically xenomorphs and the insects that they infect are like human space colonists whose
last moments will be watching parasites explode out of their bodies the insects have it a little
better i guess because they're dead before the xenomorph pops out anyway only some fungi have
worked behavioral manipulation aka zombification into this cycle and none of them infect people so
don't worry probably because they're adapted for infecting arthropods specifically which
makes it really hard for them to jump to other animals in any case the most well known of these
fungal puppet masters are probably the species of ophiocordyceps that infect and manipulate ants and
this manipulation has become incredibly fine-tuned over evolutionary time when the ants are forced to
death grip on the undersides of leaves they do it at a specific height around 25 centimeters
above the ground and at a specific time of day when the sun is highest this is probably to
ensure optimal temperature and humidity for the reproductive part of the fungi to erupt
and spread its spores which fungi often need very particular conditions to do positioning the ants
on the underside of a leaf might also give the growing fungi protection from uv damage and rain
and directing the ants to bite down around noon might ensure that by the time they die hours later
the fungi can begin to emerge at night when it's cooler researchers have even found evidence that
these fungi have tweaked their strategy over millions of years to keep up with their changing
environments see leaf biting is the typical behavior of zombified ants in tropical forests
dominated by evergreen plants but in temperate forests filled with deciduous plants which shed
their leaves zombified ants almost always perform their death grip on twigs and bark instead
to dig into this difference researchers sampled dna from ophiocordyceps fungi that infect ants
from as many locations as they could including both temperate and tropical species then they used
that data to create a family tree for these fungi mapping out the evolutionary relationships between
the different species based on their genetic similarity and this family tree suggested that
while leaf biting is the ancestral trait the shift to biting twigs and bark evolved convergently
at least four times between 20 and 40 million years ago the researchers hypothesized that
this was the result of changes in climate and environment that occurred over that period
because around 47 million years ago in the mid eocene epoch when that fossil leave from germany
dates to the world was a much warmer place and had less seasonal change back then evergreen forests
went from the equator to the far north and south even approaching the poles so it makes sense that
as the study suggested manipulating ants to lock onto leaves would have been the original strategy
but as the climate cooled during the late eocene tropical and subtropical evergreen forests were
gradually replaced by temperate deciduous forests at northern and southern latitudes zombified ants
that only gripped onto leaves in these regions would have fallen to the forest floor when the
leaves were shed and because the fungus seems to have pretty picky requirements when it comes
to temperature and humidity this would have been a major problem one that provided a pretty
strong selective pressure for ensuring that the ants spit onto something a little more secure
okay but why did such a complex ability evolve in the fungi in the first place i mean this seems
like a really complicated way for a little fungus to reproduce why not just release your spores into
the air and call it a day that's what i would do well the fossil record doesn't really give us a
clear answer the oldest known example of a fungus parasitizing ants is an ant trapped in amber dated
to between 45 and 55 million years ago and it clearly shows a fungus erupting from the ants body
specifically from its butt which is probably the most embarrassing way you could be immortalized
for eternity that's high in the list of ways i did not want to go as amazing as this fossil
is though it can't really tell us how or even if the fungus was controlling the ants behavior back
then it might have just infected and killed the ant without manipulating its behavior like many
species do today but we can use dna again to give us insights into the history of ant zombification
this time right back to its origins in a paper published in 2019 a team of researchers analyzed
the dna of over 600 species within the order of fungi to which ophiocordyceps belongs this more
extensive family tree suggested that the modern group of ophir cordyceps that zombifies ants
can trace its origins to an ancestor that infected beetle larvae now ophiocordyceps infect many
species of beetle today but those fungi don't manipulate the behavior of their hosts at all
so the researchers hypothesized that what led to the emergence of zombification
was the fact that the fungi switched hosts from solitary beetles to insects like ants and wasps
because and this is the important part those insects are more social highly social insects
like ants have some impressive group strategies to defend themselves against pathogens and one of
those defenses is what's known as social immunity the collective defenses against disease that have
developed within social groups like ant colonies see ants live in very close quarters and don't
have much genetic diversity within a colony and those are perfect conditions for the spread of
pathogens so a pretty strictly enforced public health system has evolved to keep the colony
safe ants groom each other to clean off spores quickly remove or destroy dead bodies and if an
individual shows signs of infection they're often kicked out of the colony or even killed and this
system of social immunity is pretty effective at stopping the growth of fungus from hosts that die
inside the colony it takes hours to days after the host dies for the fungus to emerge
and disperse its spores and by then the ants have usually destroyed or discarded the corpse but by
manipulating the host to leave the colony and die at a spot nearby instead usually close to a busy
foraging trail the fungi could evade the colony's social immunity and this would ensure that there'd
be enough time and the right conditions to emerge now there are still many mysteries to be solved
surrounding zombie ant fungi like how exactly they take control of their hosts to manipulate their
behavior we just don't know how they do that but this ability clearly has ancient roots stretching
back tens of millions of years over that time it's changed to suit the fungi's changing environment
as well as their changing hosts and it's this ongoing arms race between pathogen and host
that seems to have led to the emergence of zombification in the first place as the perfect
counter to a complex behavioral defense which is pretty messed up when you think about it i mean
all the ants wanted was to keep their colony free of disease and instead they got zombies
okay just to let you know we are going on a quick summer break so this is the last of us
you'll see for about a month but while we're away be sure to check out our episode
when ants domesticated fungi to learn about a much less horrible ant fungus relationship and
I'm "antsy" to thank this month's eontologists annie and eric higgins chase archambault colton
jake hart john davidson melanie lamb carnavale and alex to my become an e-night at patreon.com
eons to get fun perks like submitting a joke for me to read like this one from john
m okay here we go what dinosaur likes classic american muscle cars a camarosaurus
what a camarosaurus oh i get it and as always thanks for joining me in the atom
low studio subscribe at youtube.com eons for more evolutionary escapades
i'm so glad i got to make an alien's reference in an eon script after five years
i actually own a replica flight suit from the nostromo the first
the ship from the first movie i wear it on first date just as a vibe check yeet