Like mosquitoes, worms can be terribly harmful critters because of the diseases they spread. Take the pork tapeworm (Taenia solium) for example, which uses humans and pigs to spread its larvae and cause cysticercosis. The cycle begins with a pig, usually in a rural developing country where it's allowed to wander freely. The pig eats something contaminated with the worm's eggs, which then grow in the pig's muscles. The disease is passed to humans when they eat undercooked pork infected with the larvae. The outcome is painful. The larvae can cause lesions in the brain, muscles to swell, epileptic fits and vision problems. Luckily, anti-parasitic drugs combined with anti-inflammatory drugs can help cure the disease.