Looking on the bright side, with brain-altering parasites

 by Anne Munier

It’s been a tough year for many of us. Sometimes looking on the bright side and feeling grateful for all that we have helps. Other times, it can be even more helpful to look on the gruesome side, and be grateful that we are NOT infected with brain-manipulating parasites who take over our bodies and control our behaviour. In that vein, let’s take a moment to explore just how disturbing nature can be….

Zombie Ants

We’ll start in the humid tropics of Brazil, where a carpenter ant is living its best life with thousands of its buddies, foraging and defending the colony. No one would even notice the microscopic fungal spore that lands on it. But spores are like mini seeds, and this one penetrates the ant’s body and starts to grow inside. First the fungus feeds on the ant’s insides, and then it takes over the ant’s behaviour, compelling it to wander away from its colony, which is something that ants never do. The possessed ant climbs up a nearby plant, and clamps on with its jaws. At this point is it more ant or more fungus? Either way, the fungus is clearly in control. After finishing eating the insides of the slowly dying ant, it sends a stalk up through the back of the animal’s head. By making the ant climb up the plant, the fungus is now at a good height to spread its spores. They float out on the breeze, perhaps to infect the poor ant’s relatives, and the cycle starts anew.

 

A zombie ant, in the final stages of serving its fungal master - Photo Credit Bernard Dupont

A game of cat and mouse

Toxoplasmosis is a tiny parasite that infects mammals and birds around the world, but it’s mice that really need to watch out. When the parasite completes the life stage that takes place inside a mouse’s brain, it needs to make its way into cat intestines in order to reproduce. How can this microscopic parasite accomplish that? By encouraging its mouse host to be eaten by a cat! Under the parasite’s influence, mice stop being their usual fearful, cautious selves and start exploring more. They actually become attracted to the smell of cat urine (I know!!). This really increases the chances that a cat and infected mouse will find each other- good news for the cat, bad news for the mouse, and great news for the toxoplasmosis!

 

A parasite that makes mice love cats?

Baby birds taking over the nest

Not all parasites are tiny, and they don’t necessarily need to get into an animal’s brain in order to manipulate them. Some birds, like cuckoos or brown-headed cowbirds, are “brood parasites”; they’ve figured out that sneaking their eggs into the nests of other birds saves them a lot of time and energy on the parenting front. The unwitting foster parents may be suspicious, but very often they accept the egg and raise the chick as their own. The imposters tend to be the first to hatch, beg the loudest, hog most of the food, and grow the most quickly. In the case of some cuckoos things can get really nasty- the cuckoo chick hatches before the others and actually hauls the other eggs out of the nest (effectively killing its foster siblings, and ensuring that it gets all of the parents’ care). These darling babies can grow several times larger than their run-down caregivers, all while intently demanding regular feedings.

Mama warbler feeding her insatiable foster chick, the common cuckoo- Photo credit: Harald Olsen

 

Is anyone else wondering whether we humans could have parasites that, unbeknownst to us, are manipulating our behaviour? Quite possibly! Initial research suggests that people exposed to the flu virus become more social- going to more parties and visiting more friends. No strong conclusions have been reached yet, but some researchers suspect that the virus is influencing its human host’s behaviour in order to expose it to as many people (and potential new hosts!) as possible.

Love ‘em, hate ‘em or just feel grossed out by parasites, but it’s hard not to be impressed by some of the tricks that they’ve come up with. Now doesn’t life seem a bit better, knowing that we’re (most likely) not possessed by parasites controlling our thoughts, actions, and taking over our very being?