The invisible world
It is well known that nature can be ruthless sometimes. But you don't often see it as colourful as microbes make it. Where predators and carnivorous plants simply devour their prey, some microbes have a more sinister approach. Parasitic fungi turn their victims into mindless zombies by penetrating their nervous systems, drugging them or taking over their muscles. How Halloween can it get ? Header image by © Andreas Kay
Like all life, these fungi have only one goal: to reproduce and spread. But unlike many other species, they have found a unique way to do so. Fungi of the genus Ophiocordyceps are masters at holding their arthropod victims hostage. More than 200 species of Ophiocordyceps fungi infect ten different species of insects and arachnids. The fungus eats the insect from the inside out, makes new spores, and spreads to the next victim. But to increase the chance of successful sports distribution, the fungus causes the insect to do something unnatural. A good example of this is shown in the image on the right.
Ophiocordyceps unilateralis occurs in the Asian tropics where he turns ants into zombies. Once inside the ants body, the fungal threads form a network in and around the muscles. In this way they force the ant to leave the nest and look for it higher up. The bewitched ant climbs into a plant, bites itself at the bottom of a leaf in the vein, and waits for death. After a few days, the ant’s head bursts open, and a fruiting body full of spores grows outwards. And because of the elevated position of the ant carcass, the spores spread extra far.
Some fungi go a step further and influence the behavior of insects by infecting their brains. Entomophthora muscae, literally translated as ‘insect destroyer of the fly’, penetrates the nervous system of a fruit fly (Drosophila melanogaster) and leads it to its death. A few hours before his death, the fungus forces the fruit fly to climb to a higher place. There it bites itself into something, raises its abdomen and spreads its wings. In this way, the fly clears the path for the contagious spores that the fungus spreads after it has broken out of the fly’s abdomen.
However, it can be even stranger. American cicadas spend the first 13 or 17 years of their lives underground. On their way out, some of them come across traces of the Massospora fungus. A week after the infection, the abdomen of the cicada falls off, and a white ball of fungal spores becomes visible. The fungus has grown throughout the insect and has eaten all its organs. Meanwhile, the ‘assless’ insect lives on as if nothing is wrong. The fungus has drugged the cicada with a hallucinating substance. And while the tripping cicada flies around, other cicadas are buried under a deadly rain of spores from its zombie-fungal butt.
But microbes do not only influence the behavior of insects. Large animals are also targeted by them. The single-celled parasite Toxoplasma gondii can only reproduce in felines. And to get there it has developed a bizarre trick. Rodents are no longer afraid of cats after an infection with this microbe. They react slowly to danger and don’t flee when a cat comes near them. In addition, the mouse is brainwashed so he feels attracted to the smell of cat piss. The helpless rodent is devoured, and the parasite can infect the cat.
