This semester I'm taking
Insect Ecology. Our first assignment was to watch a movie or read a story about giant insects and then write about why that scenario is biologically impossible. I had a hard time choosing a movie since most giant bug movies are found in the "Horror" section and I don't watch scary movies. But then I came across this little gem,
Eight Legged Freaks. It was not scary at all... a little gross at times, but not scary. If you're into cheesy movies about giant spiders, this one is for you! If you're not, then you can just read my assessment below. It summarizes the movie and explains why you never need to worry about giant spiders. Enjoy!
-A :-)
2002 was an amazing year. The Patriots won the super bowl, Michael Jackson dangled his
small son over the edge of a balcony, the Enron scandal was just heating up, we
were rocking out to Usher, Jennifer Lopez, and Eminem, and we were cheering for
our favorite winter Olympic athletes in Salt Lake City. But really, what should stand out the
most to all of us looking back on 2002, is the fact that this was the year that
Warner Brothers came out with its arachno-classic, Eight Legged Freaks, starring David Arquette and a young Scarlett
Johansson. Set in the Arizona
desert town of Prosperity, this film is an epic story chronicling the result of
dangerous chemicals falling off a truck to contaminate a pond ironically close
to an exotic spider farm. The
cause of the chemical spill was, of all things, a small rabbit in the
road. The result of the
spill? “Spider steroids,” crickets
that were collected from the pond and subsequently fed to around 200 exotic
spiders, causing them to grow unusually large in very short amounts of time.
First
off, this movie deserves some scientific props. A good variety of spiders were included, and their external
morphology seemed pretty accurate.
Eight legs, two body segments, diognostic eye patterns for different
groups, silk coming out of spinnerettes at the posterior end of the spiders,
and sexual dimorphism were obvious throughout the movie. The tarantulas were
appropriately attacking folks using their fangs in a parallel up-down motion
charactaeristic of the mygalomorphs (as opposed to a scissor motion that the
more common araneomorphs would use).
The orb weavers were subduing their prey in silken cocoons before externally
digesting them using gastric enzymes then ingesting them with their sucking
stomachs. It’s good that most of
the spiders were night hunters since the dark exoskeletons plus the large
surface area exposed to the sun’s radiation would heat those spiders up pretty
quickly. With such small surface
area to volume ratios, it would be easy for the spiders to absorb and retain
heat, and difficult for them to lose heat, possibly reaching a lethal
temperature threshold, which would kill the spiders, if they hunted by day.
Now
let’s talk about why we never truly need to worry about a giant spider
attack. First of all, there’s the
exoskeleton. There is no way that
an arachnid exoskeleton would be able to support a body the size of a small car. If, by some miracle, it could, the
spiders would have to be very slow and clumsy, dragging all that weight
around. They would not be able to
so agilely jump over boulders, cars, and buildings, and travel a city block in
one great leap. The jumping ability
of the giant spiders is in and of itself is an issue as well. Sure, small spiders and other insects
can jump very far distances compared to their body sizes, but when you’re that
tiny, the forces at work on you are very different from what we humans are used
to. Gravity has very little effect,
and smaller intermolecular forces are much more important. Once the spiders’ size is scaled up,
gravity is going to have a much different effect on the body, making the
leaping spiders in the movie impossible.
In addition to less interaction with gravity, normal-sized hunting spiders
have specialized hairs on their legs called scopulae, that help them adhere to
surfaces like walls, ceilings, buildings, people, etc. Again, when the spider
gets scaled up to such a great size, the scopulae are no longer going to be
sufficient for gripping vertical surfaces without falling. So the giant spider climbing up the
man’s back and up and down all sorts of walls and buildings is just impossible.
Most
spiders respire through structures called book lungs, a series of membranes
that together actually look like pages of a book. Oxygen enters the spider’s body through these
membranes. Multiple thin membranes
like this are great for increasing surface area for the diffusion of gases, but
this increased surface area presents a danger of desiccation. This is one of the main reasons that
many spiders are nocturnal, and stay in their burrows during the heat of the
day. However, even though most of the
“eight legged freaks” of the movie restricted their hunting to nighttime, the
book lungs of spiders the size of cars would have to be incredibly huge. With that much surface area exposed to
air, especially air in the arid Arizona desert, these giant spiders should have
died from desiccation very early on.
But let’s say that there was some
mechanism that prevented the spiders’ lungs from drying out. There is still the issue of an open
circulatory system that relies on diffusion for gas exchange. Spiders, like insects, do not have the
complex heart/blood vessel circulatory system that humans are familiar
with. Their “blood” is hemolymph,
and it fills the body cavities without the restriction of blood vessels. (The hemolymph was depicted in the
movie as a nasty green goo that exploded out of the spiders when they were
shot… an accurate enough depiction, I guess.) This hemolymph bathes the internal structures of the spider,
transporting nutrients, wastes, and gases. There are some muscular contractions that can facilitate a
type of hemolymph “flow” around the body, but all the molecules within the
hemolymph get moved around passively via diffusion. It would be impossible for a spider as large as the ones in
this movie to establish a concentration gradient efficient enough to properly
nourish and oxygenate all the body tissues. Without efficient oxygen and nutrient delivery and waste
removal, the spider’s tissues (including organs and muscles) would stop
functioning, most likely have some debilitating muscle cramps, and the spider
would die.
Did
you know that spiders do not have extensor muscles in their legs? It’s true! A spider’s ability to extend and move its legs depends solely
on hemolymph pressure. That is why
when spiders die, their legs almost always curl up so tightly around their
bodies. I can’t imagine the amount
of hemolymph pressure that would be necessary to move the giant legs of the
spiders that attacked the town of Prosperity. There really is no way a sufficient amount of pressure would
be able to be generated in a spider’s open circulatory system.
It
was realistic for the citizens of Prosperity to be finding some molted
exoskeleton pieces around town, but they really should have found a whole lot
more of those discarded exoskeletons.
Spiders, like other arthropods, are unable to grow without shedding the
confines of their current exoskeleton.
Typically, a spider like a tarantula will molt around ten times as it
grows from an immature to an adult.
Each time the spider molts, a newly formed exoskeleton that was formed
below the current one is exposed.
Each new exoskeleton expands to accommodate the spider’s growing body
size before hardening. If the
spiders depicted in the movie really grew from normal size to super-sized in
just a few weeks, there had to have been an unbelievable number of molts! Exoskeletons and pieces of exoskeletons
should have filled up that mine and littered the streets.
One
final point on why this movie is unrealistic doesn’t have to do with the size
of the spiders; it has to do with their life habits. Most spider species are cannibalistic. If you were to have multiple spiders
for pets, you’d need to have separate cages for them unless you want to come
home one day to find out that Billy the Spider had eaten Tommy the Spider. This is why spiderlings disperse after
emerging from their eggs, often using the wind and a bit of silk from their
spinnerettes to up to 100 km. If
they didn’t do this, siblings would pretty quickly start eating each
other. Thus, the vision of a giant
pack of spiders hunting the humans in this movie is pretty silly. Especially since the spiders were of
multiple species. Sure, the humans
maybe seemed like “easy” prey, especially after most of the small pets in town
had already been consumed, but instead of trying to break through doors and
walls and mall gates to chase the humans, real spiders probably would have
started eating each other.
Eight Legged Freaks had classic happy
ending, the guy got the girl, the town listened to the kid, the sketchy mayor’s
mall blew up, and gold was once again discovered in the mines of Prosperity
(despite the fact that the mines exploded at the end of the movie). However, if the gold boom doesn’t last,
and no one thinks to capture, sell, and use the natural gas filling the mine
shafts, the people of Prosperity have another option—collect and sell the
spider silk that was left all over town!
The silk of a normal spider is said to be strong enough to catch and
stop a 747 jet mid-air. Bioengineering research is currently underway to use
spider silk to make fabrics for things like bullet-proof vests, cables, gloves
and parachutes. I would love
the chance to be able to hold and manipulate the silk of such giant spiders,
and a material that strong in such vast amounts has to be worth a lot of money
to someone… certainly enough money to allow the citizens of Prosperity to continue
to thrive in their small town.
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The difference between utility and utility plus beauty is the difference between telephone wires and the spider web.- Edwin Way Teale
