hi and welcome to facts in motion
Human zombies are still a thing of fiction,
but in the animal world, mind control is actually
more common than you might think.
But unlike in movies where it's usually a virus
that turns people into the walking dead, in the real world
parasites are the most common cause for this phenomenon
one example of this parasitic mind control
is found in spiders, more specificaly in
orb weaving spiders of the genus Cyclosa
one of the biggest threats these spiders face
is a wasp species of the family of scorpion wasps
a parasitoid wasp family
that has adopted a very special strategy for reproduction
while most wasps practice either mass provisioning,
where all the necessary food for each of the offspring is stocked with the eggs in a small chamber,
or a progressive provisioning where the larves are fed directly
and continually during their development
scorpion wasps instead inject the eggs into or on the bodies
of living hosts
this provides the larvae with a continuous supply of food
until they're big enough to pupate a few weeks later
at this point, the hosts usually die
and the larvae emerge, and begin their metamorphosis into adult wasps
While each species of these wasps are usually specialised on a
specific host,
collectively, scorpion wasps use a diversity
of different hosts
with the most common being the larvae and pupae of butterflies, beetles, flies,
and other flying insects.
But what's so special about the case of Cyclosa
it's not that the host is a spider,
but how the spider is manipulated by the wasp larva
and turned into a mind-controlled worker.
After the larva spends a few weeks
living and growing on the spider's body and using its teeth-like structure
to suck the spider's blood,
it is ready to pupate.
At this point, the larva injects a substance into the spider's body.
What exactly the substance is and how it works is still unknown,
but its effects on the spider are drastic.
After the injection, the spider exhibits a significantly-altered behaviour.
Instead of going about spider business, it starts to completely rebuild its web for the wasp like a mindless zombie.
First, it removes all spiraling threads
that makes the webs of orb weavers so appealing
and are normally used to catch the spider's prey.
They won't be of any use for the larva.
The (?) of the webs, however, remain,
and even get reinforced with additional strings
and then decorated with special-fabric silk
that reflects ultraviolet light.
This warns away birds and some large insects from accidently flying into the web and destroying it.
The improved visibility and increased strength of the web
are very important to keep it intact during the larva's two-week metamorphosis.
When the spider's finished building the perfect nest for the larva,
it returns to the center of the web
and sits inert, patiently waiting for its own death.
With no further use for it, the larva kills the spider
and sucks it out completely before throwing its empty shell off the web.
Then, it settles down in the center of the web
to spin itself a cocoon in which it will transform itself
into a wasp within the next 10 to 15 days.
The spider's bespoke creations are,
like researchers from Japan found out,
not a completely new design by the parasites.
Instead, the larvae were corrupting a natural behaviour of the spiders.
Spiders which are about to moult bear a very similar one,
called the "resting web" that is used as a temporary hangout
during its two-day moulting process.
But a web that lasts only two days isn't going to cut it for the larvae,
which explains why the threads the spider uses to construct the larvae webs
were significantly thicker and tougher, requiring 2.7 to 40 times the breaking force to snap
than the threads of a normal web.
From an evolutionary standpoint, this makes it relatively easier for the larva.
Instead of having to mind-control every step of modifying the sticky web for its needs,
it just has to turn on an already existing behaviour program
and slightly alter a few variables.
How exactly the larva does this is, however, still a mystery.
One theory is that the chemicals injected by the larva
are similar to the hormones the spider produces naturally before moulting.
And that this is what motivates the spider to start building the nest for the larva.