6 Acanthocephala is a parasite that causes some animals to lead themselves to their death because a parasite is “brain-jacking” them. Acanthocephala is one such parasite which infects crustaceans and forces them to swim to the water’s surface so they’re eaten by ducks.

Also known as “thorny-headed worms,” Acanthocephala has spines through which they pierce and hold the gut wall of their host. Their life-cycles are very complex and involve at least two hosts who could be mammals, fishes, birds, or amphibians. They begin their life-cycle by occupying vertebrates who live in marine or freshwater bodies. A small crustacean, Gammarus lacustris, is often preyed upon by the parasite. The crustacean’s innate nature is to avoid light and remain in the depths of the water to avoid being preyed upon by ducks. But once infected, the parasite influences the crustacean’s behavior making it swim on the surface by attracting it to light. It can also make the crustacean latch itself on a rock or plant so that ducks can spot it and eat it. For the Acanthocephala to thrive, it is necessary for the duck (second host) to eat its first host.

Their life cycle goes like this… the host excretes the parasite’s egg through its feces which is then ingested by a crustacean or another arthropod. It develops when in the body of the intermediate host and grows mature and mates in the body of its final host. The process then repeats. There have been a few cases of human infections but they are treatable. (source)

7 Pleistophora mulleri is a parasite that makes shrimp consume much more of their own kind drastically increasing their cannibalism and making them take much less time to consume their prey.

Parasites can be ruthless and Pleistophora mulleri is an example of that. It can make the indigenous shrimp Gammarus duebeni celticus consume its own kind much more than its usual eating patterns. Researchers have found that the parasite drastically increases the indigenous shrimp’s cannibal-like traits and also makes them more voracious leading them to consume their prey in a far shorter time than the uninfected ones.

The parasite relies on the host for food, and millions of them latch themselves in the host’s body. It is because of the increased demand for food that the shrimp become more voracious and cannibalistic. The Irish waterways have seen the shrimp species Gammarus duebeni celticus replaced by the invasive species Gammarus pulex. Researchers have stated that the parasite is responsible for the weakening the resistance of the former. (source)

8 Nycteribiidae and Streblidae are two families of the species of horrifying parasites which are flies that attach themselves to a bat’s head and suck its blood.

If you thought bats were horrifying, wait until you hear about the bat flies. About 275 species in the Nycteribiidae family and 225 in the Streblidae family suck bat blood. The bat flies belonging to the Nycterbiidae family are wingless and have a spider-like appearance, while the ones in the Streblidae family have functional wings. These bat flies who have evolved over millions of years spend their entire life cycle clinging to the bodies of bats, particularly to their fur and wings. Researchers believe that 20 million years ago before these flies evolved, they would have consumed bat’s sweat, feces, and dead skin. Two days after being separated from their host bat, the bat flies die. (1,2)

9 Ribeiroia ondatrae is one of the most horrible parasites on the planet. It forces frogs to have several defects like multiple legs that jut out at weird angles to affect their mobility to put them in danger of predators.

A flatworm parasite, Ribeiroia ondatrae, infects frogs when they are still developing their limbs. It leads to several defects in the amphibians like no legs or multiple legs that pop out at weird places in the body. This makes it difficult for the frogs to move and makes it easy for the predators to feast upon them leading to an early death. This parasite, which is a grave threat because it is constantly moving, can also land in an area where endangered or threatened species form a habitat. Scientists have been trying to predict the places where these malformation-causing parasites could exist to prevent further harm to the animals.

The life-cycle of this parasite begins with a ramshorn snail where it asexually clones itself, converting the snail into a “parasite machine” of a kind. Hundreds of parasites are released by the snail every night looking for their second hosts, the tadpoles. The tadpoles grow up to become a frog with defects which are quickly eaten by birds. The birds are the third host. The parasite reproduces inside the birds, the eggs are released to the feces of the birds, and the cycle repeats. (source)

10 Diplostomum pseudospathaceum is a parasite that lives inside the eyeball of a fish and controls its behavior. When young, the parasite protects the fish. When it grows, it leaves no stone unturned to get the fish eaten by birds.

Imagine a parasite pulling the strings from inside the eyes of a fish! Diplostomum pseudospathaceum is a parasite that changes its host’s behavior to fit its needs. Beginning their life cycle with a snail, the parasite then finds its way into the eyeball of a fish by penetrating the skin of the fish in the water and hiding out until maturity. When young, it protects the fish so that it can grow, but once it is mature, it will do all it can to get the fish eaten by a bird so that its life cycle can continue inside the bird’s body. The parasite mates in the bird’s digestive tract and its eggs are released through its feces like many other parasites. In a 2015 study, it was revealed that fish infected with the immature parasite swam slower than the uninfected ones making them less visible to prey. It was also found that the fish that were infected with the mature parasite swam much more actively than the uninfected ones. (source)