Hijackers in Nature

With the fear of COVID-19 haunting the public, many of us have become warier of people coughing and sneezing around us. This sparked some random thoughts in my mind. I understand that our bodies produce mucus to deal with the viral infection. Coughing and sneezing out the mucus are ways for our bodies to get rid of the virus. Wait a minute… what if the virus has a ‘mind’ of its own? Then maybe it has the intention of proliferating by making people cough and sneeze, or by exploiting our bodies’ immune response to spread itself to even more people.

This sounds like something straight out of a zombie apocalypse film where individuals infected with a virus turn into mindless creatures with the sole purpose of biting others to spread the disease. So the question of the day is – will there ever be a zombie apocalypse? Well, the idea of a zombie apocalypse doesn’t sound too absurd when we look at examples of hijackers and brainwashers in nature.


The most famous example is a parasitic flatworm known as the green-banded broodsac (Leucochloridium paradoxum). It is typically found in a genus of land snails. In the larval stage, these tiny worms are accidentally consumed and travel into the digestive system of the snail to develop further, where they invade the snail’s eyestalks.


This turns the snail’s eyestalks into bulging and colourful displays resembling light sticks at concerts. This pair of light sticks also look like juicy caterpillars. Yum! The invasion also “brainwashes” the snail to expose itself to better-lit places, allowing the poor snail to be spotted by predators such as birds. After a bird gobbles down the snail, along with the parasitic worms, the worms will grow within the bird until they reproduce and lay eggs. These eggs will then be passed out together with the bird’s droppings. The next unwary snail then consumes the eggs, completing the parasite’s life cycle.

Land snail with Leucochloridium paradoxum in the left eyestalk
Photograph by: Thomas Hahmann / CC BY-SA 3.0

If you think that is repulsive, then let me introduce Sacculina, the parasitic castrating barnacle! But fret not, this genus of barnacles only parasitises crabs. The female Sacculina larva finds a crab and heads straight for the more vulnerable parts of the crab which are usually the leg joints. From there she injects her soft body into the crab. She slowly nourishes herself and grows in her rental apartment, the crab. As she matures, she emerges as a sac on the underside of the crab, where crab eggs would usually be incubated. The parasite will then lie in wait for her male counterpart to come and mate so that she can produce her own eggs. The invasion of the Sacculina is a nightmare for the crab!

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After the invasion, the crab is now unable to moult, impairing the crab’s overall growth. This is mainly due to a loss of nutrition, as all nutrients are re-directed to the parasite’s eggs. Ultimately, this infestation results in the castration of the crab by destroying its gonads, rendering the crab permanently infertile.

That’s not all! If the invaded crab is a male, the parasite forces a hormonal change in the crab’s body. The effects of this hormonal change are ghastly, as the male crab is manipulated into changing his anatomy and even behaviour to become that of a female crab. This eunuch crab, carrying “her” illegitimate eggs, nurtures the eggs until they hatch. Talk about a surrogate slave!

A parasitical barnacle on a female swimming crab
Photograph by: © Hans Hillewaert / CC BY-SA 4.0

Nature certainly has her ways to shock and fascinate us in a myriad of ways – from mind-controlling fungi to worms that will make snails commit suicide; from castrating barnacles to viral outbreak. So back to the question – will there ever be a virus that can cause something like a zombie apocalypse? Judging from the existing “zombie” examples that we have in nature, it is possible. But one thing is for sure, we can reduce the spread and damage done by a potential viral outbreak like COVID-19, by remaining calm and being responsible for our own actions in such situations. So…start washing those hands and taking your temperature regularly!

Written by See Eng Sheng
Illustrations by Jasreel Tan

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