Science
Parasites & Symbiosis Quiz 🦠
Mind-controlling fungi, zombie ants, and the organisms living inside you right now.
Mind-controlling fungi, zombie ants, and the organisms living inside you right now.
Approximately 30–50% of the global human population is infected with Toxoplasma gondii — a mind-altering parasite that reproduces only in cats. From zombie-ant fungi to the trillions of bacteria helping your digestion right now, parasitism and symbiosis are everywhere. This hard quiz covers the science of organisms that live at the expense of others — and those that thrive together.
Each round presents 10 randomized multiple-choice questions drawn from a pool of 50, so every playthrough is different. You get instant feedback with explanations after each answer, plus a shareable score at the end.
You'll explore Ophiocordyceps zombie-ant fungi (the inspiration behind The Last of Us), Toxoplasma gondii's influence on human behaviour, the three types of symbiosis, the human microbiome's 38 trillion bacteria, fecal transplants, Guinea worm eradication, and nature's strangest parasitic plants and animals.
Yes — several parasites manipulate host behaviour to complete their life cycles. Ophiocordyceps fungi force carpenter ants to climb plants and clamp onto leaves before killing them. Toxoplasma gondii makes rodents attracted to cat urine so they are eaten, allowing the parasite to return to its definitive cat host. Leucochloridium flatworms turn snail tentacles into pulsating displays that mimic caterpillars to attract bird predators.
The human gut is home to over 1,000 species of bacteria — roughly 38 trillion microbial cells, slightly outnumbering the 30 trillion human cells in your body. This gut microbiome weighs approximately 2–3 pounds (1–1.5 kg) and produces about 95% of the body's serotonin, playing a major role in digestion, immunity, and even mood through the gut-brain axis.
By deaths per year, Plasmodium falciparum — the malaria parasite — is the most dangerous, killing over 600,000 people annually, predominantly children under five in sub-Saharan Africa. The parasite is transmitted by Anopheles mosquitoes and invades and destroys red blood cells. Guinea worm (Dracunculus medinensis) was once devastating but is close to eradication thanks to the Carter Center.
Last updated: March 2026