I sat down recently with my girlfriend to watch Alien - a movie that I hadn’t seen in a long time. As you might guess from my granny-murdering epic on the flight-or-fight response, when I see a good horror movie I think two words: blog article. The classic chest-bursting, cat-rescuing, android-killing sci-fi horror flick got me thinking about parasites and how there were some I know of that are freaky-as-hell. So, in my typical fashion I began to do some research on some of the most incredibly nasty ones I could find.
This article is, quite fittingly for the time of year, not
for the faint of heart. Join me as we delve into some of the most
stomach-turning little critters that nature has to offer…
Cymothoa exigua
| The tongue-eating louse. You would think the fish would notice... (source) |
‘Ewww’ I hear you say. And right you are. But don’t worry –
it doesn’t chow down on human tongues (as far as we know *scary music*) – it
likes to dine on fish. The louse enters the body of the fish through the gills
and attaches itself to the base of the tongue. This adorable little critter
then begins to drain the blood from the tongue through the claws at the front
of its body. The tongue eventually shrivels up and the louse attaches itself to
the remaining muscles where it actually becomes
the tongue of the fish. Perhaps the strangest fact about this relationship is
that the fish continues to use the louse as its tongue, suffering no ill effect
whatsoever (other than losing their tongue and having it replaced with
something out of a Ridley Scott movie).
Scientists reckon that, despite its horrifying appearance
and habits, this parasite is benign. Though I expect if one were to ask a fish
suffering from this particular affliction, it might offer an alternate opinion.
That somehow brings me on to a worm that can control the behaviour of the host
it infects.
Dracunculus medinensis (Guinea worm)
| The young guinea worm - I mercifully decided not to include a photo of the worm hanging out of some poor dude'sleg. (Source: CDC Public Health Library) |
As with most
parasites, part of the life cycle of this adorable little worm partly takes
place in a second type of host. The parasite larvae are initially eaten by
water fleas which are then ingested by humans drinking unfiltered water. The
fleas are broken down in the stomach acids of the unfortunate host, leaving
behind the Guinea worm larvae. The larvae escape into the stomach lining and intestine
where they mature and develop into an adult worm measuring something like two
or three feet in length (I know – the more you learn about this thing, the less
you like it).
When it comes time
for the young worm to ‘sow its wild oats’, it migrates to the surface of the
skin – usually in the lower portion of the leg. This is where it gets
weird(er). The worm creates a blister on the surface of the skin and induces a
burning sensation which causes the host to seek the comfort of some nice cold
water. When the blister in question is submerged in order to provide some
relieve from the burning sensation, the worm (now poking its wormy little head
out of the host) releases its larvae into the water – thus starting the whole
unpleasant cycle all over again.
Ophiocordyceps unilateralis – zombifying
fungus
| A victim of O. unilateralis - yes, that a mushroom growing out of it's head. (Source: PLoS One) |
Anyway- not much is
known about the life cycle of this fungus, but scientists believe that the
fungal spores enter the ant’s body and begin to develop, all the while
consuming the insect’s soft tissues. During this horrific process, the fungus
produces compounds which alter the ant’s behaviour, turning it into a ‘zombie’.
When this happens, it begins to convulse and falls out of the tree it usually
lives in. After it hits the ground, the ant finds a plant, climbs the stem and
clamps itself to a leaf vein with force far in excess of its usual abilities.
At this point, the ant dies- but the fungus continues its grizzly work.
The fungus continues
to grow throughout the ant corpse, consuming the rest of its soft tissues and
structurally reinforces the exoskeleton of the unfortunate victim. The fungus
also sprouts outside of the ant where it completely anchors the ant to the
plant (hey, look at that – I made a rhyme!). Finally we make it to the nastiest
part – when the fungus is ready, a mushroom (or fruiting body) grows out of the
dead ant’s head where it releases its spores into the environment.
I imagine we are all
too grossed out at this point to enjoy a smart-ass comment, so I won’t make one. Moving
on.
Leocochloridium Paradoxum – zombifying flatworm
| An infected snail. No, it's not a snail who has seen an attractive lady snail to it's left. Photo by Thomas Hahmann |
The flatworm larva
hangs about on the ground until it is hovered up by a passing snail – its
intermediate host. The flatworm is now presented with a new problem – birds
don’t really like to eat snails much either. One thing they do like to eat,
however, is caterpillar (I am going somewhere with this, don’t worry).
Inside the snail the
developing flatworm migrates to the eyestalks (weirdly, they seem to prefer the
left one) where they grow into broodsacs. This process has a dramatic effect on
the antenna of the snail – the broodsac causes the stalk to elongate, swell and
turn bright green and yellow. That’s right – it makes it look like a
caterpillar. Now for the clever part. The infection of the eye changes the
snail’s sensitivity to light, causing it to mindlessly seek out light, open
areas – which is kind of like lighting up an ‘ALL YOU CAN EAT BUFFET!’ sign for
birds flying overhead.
The poor zombified snail is then eaten by a bird which
thinks it has a caterpillar stuck to its head. The flatworm then finishes its
development in the bird with its larvae being excreted back to the earth,
beginning the whole cycle all over
again.
Cotesia Glomerata – the real ‘Xenomorph’
I’ve saved the best
for last – this horrible little creature is the real-life inspiration behind
the iconic scene from Alien you can’t
un-see: the chest-bursting scene. When the writers of Alien were coming up with the scene that would freak out a
generation, they looked to Cotesia glomerata- a parasitic wasp. Now, wasps are scary at the best of times- but this
one takes the cake.
Thankfully Cotesia doesn’t prey on humans, but is
the bane of the white butterfly – giving it its common and vaguely cuddly name
of the White Butterfly Parasite. Don’t let the name fool you – this is one
nasty little bugger.
The whole thing starts when the female wasp injects its eggs into the
caterpillars of the white butterflies using a needle-like organ called an
ovipositor. Over a 14-day period, the wasp embyros consume the caterpillar from
within, developing into larvae inside the body of the wasp with the size of the
brood reaching up to 50-60, with each larva being about the size of a rice
grain. While the larvae develop within the caterpillar its behaviour is altered
– it gorges itself, eating 1.5 times its usual food intake to nurture its unwanted
passengers.
An interesting little side note here is how the eggs survive when
initially injected into their host. Normally when a foreign body enters the
circulation of a living organism it is usually neutralised and cleared by the
host immune response. In order to overcome this threat, the White Butterfly
Parasite eggs are coated in a virus which paralyses the insect’s immune
response. The virus is actually genetically coded in the wasp’s DNA.
Anyway, back to the zombified-caterpillar-wasp-incubator. While the
larvae are growing inside the caterpillar they are careful not to actually kill
the host – only drinking its blood and never damaging the vital organs. This is
a characteristic shared by the most effective parasites – they keep the host alive.
When their two –week development is up, the larvae are ready to emerge and the
scene from Alien begins.
| Someone get Ellen Ripley... and tell her to bring a pulse gun. (source) |
You might think it’s no walk in the park being a human
being - but if you imagine you could instead be a
snail, an ant or caterpillar living in that park, things probably don’t seem
that bad.
Happy Halloween, internet folks! Remember to like the Facebook page to help support and receive updates from ScienceUnplugged!
As much as these parasites are interesting to read about,
parasitic organisms are a huge problem in developing countries where they can
be a leading cause of disease and death in humans. If you would like to know
more about the issue or donate money to help combat tropical diseases please
feel free to check out the Bill and Melinda Gates Foundation, UNICEF and the
World Health Organisation.
As with every article I post here, this one has been thoroughly researched and a list of sources can be provided for anyone who is curious – just check out the contact page
As with every article I post here, this one has been thoroughly researched and a list of sources can be provided for anyone who is curious – just check out the contact page

