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We rightfully fear the internal assault of parasitic worms and feel disgusted by mosquitoes, leeches, and mites. These classic parasites are just a glimpse of the true horrors out there. Much worse creatures lurk in search of a host. These are the macroparasites: fully grown animals that latch onto other species, including humans. Prepare to witness the shark that behaves like a leech, the bloodthirsty starling, and the surprisingly perilous lamprey.
10. Castrator Barnacle
Barnacles on ships and the painful cuts from barnacle-laden beaches are unpleasant enough, but the Sacculina is the most grotesque macroparasite imaginable with its strange attacks on crabs. The female Sacculina larva locates a crab and begins walking on its surface until it finds a joint. Then, it molts and injects its soft body into the crab, causing the crab's shell to fall off. The Sacculina develops inside the crab, eventually forming a sac on the underside of the crab's rear thorax, the area where its eggs would normally be carried. Once fertilized, the female castrates the male crab and transforms it into a female by injecting potent hormones. The now-transformed crab will care for the newly emerged barnacles as they take on crab-like forms. The toxic hormones also stunt the crab's growth and prevent it from regenerating lost claws.
9. Sea Lamprey
The Sea Lamprey is a jawless fish with an eerie, nightmarish look. Growing up to six feet long, this cartilaginous creature features a circular mouth lined with razor-sharp rasps that tear into the flesh of its host fish. The Lamprey patiently waits for large fish like salmon, perch, or bass, then strikes quickly, attaching itself with a powerful sucker and scraping at the flesh. It may remain latched on for several days before detaching, behaving much like an enormous leech. The wounds inflicted by the Lamprey can lead to secondary parasite infestations and fungal infections. Disturbingly, there have been cases where swimmers in lakes have been treated for painful body scrapes after becoming unwitting hosts to these creatures.
8. Sharp-beaked Ground Finch
In nature, the most unexpected creatures can offer startling revelations as evolutionary forces turn the tables and upend expected roles. The Sharp-beaked Ground Finch is a cousin of the colorful tanagers and sparrows commonly found in North American gardens. However, this South American songbird serves as a remarkable example of evolution's flexibility, transforming an innocent creature into a sinister parasite. Measuring just 4 inches long, the Ground Finch approaches resting petrels, gulls, and marine iguanas, using its large bill—initially designed for cracking seeds—to slash blood vessels and remove surface tissue. The tiny bird then feeds on the blood before moving on to its next victim, often before the host has a chance to react. The gaping wounds caused by the bird’s beak are highly susceptible to infection under the scorching tropical sun.
7. Oxpecker
The Oxpecker is a tropical bird measuring about 8 inches, native to the grasslands of Africa. If you observe a giraffe, elephant, or rhinoceros, you’ll often spot a group of Oxpeckers clustered around the animal’s vulnerable facial areas. For a long time, scientists believed this behavior was an example of mutualism, with the birds removing lice and ticks from the animals. However, it has now become clear that this once-praised bird is far more sinister. Nietzsche's warning, 'to take care when fighting monsters lest we become monsters ourselves,' resonates as we learn that the Oxpecker has evolved into a parasite in its own right. Not only do they remove insects, but they also use their bills to enlarge the wounds they create, feeding on the host's skin, blood, and plasma.
6. Cigar Shark
When we think of a shark attack, we typically picture a massive predator from the surface ripping off limbs or tearing flesh. However, there is a much stranger and more disturbing reality. Scientists were perplexed by mysterious circular wounds on sharks, whales, and fish until they discovered a 15-inch long shark with a round mouth and oversized teeth. The Cigar Shark is a type of dogfish that inhabits the dark depths of the ocean and rises as much as a mile during the evening to parasitize larger prey, attaching itself to remove chunks of flesh before detaching. Human encounters are rare due to the shark’s deep-sea habitat, but when they do occur, they lead to painful, unsettling wounds from this bizarre parasite.
5. Pea Crab
Let’s now explore a case where the crab is not the host, but the parasite. We often picture crabs as independent, agile predators and scavengers, but the Pea Crab leads a far more grotesque existence. Measuring up to 1 inch (2 centimeters) in size, Pea Crabs invade their filter-feeding oyster hosts in their juvenile plankton form. Once swallowed, they avoid digestion and grow into fully developed crabs within the shell, pushing aside internal organs and moving around while siphoning oxygen and nutrients from the host. The oyster suffers minimal harm, but the Pea Crab pays for its parasitic lifestyle with a lifetime spent imprisoned within the shell.
4. White-Winged Vampire
We are all familiar with the terrifying tales of Vampire Bats that swoop down to feed on the blood of goats and even humans, spreading the deadly rabies virus. However, there exists a much more obscure and unnerving species of blood-sucking bat with a truly unsettling lifestyle. The White-winged Vampire is a parasitic bat that has evolved to specifically target birds as its hosts. Waiting patiently in the treetops, this vampire bat descends upon unsuspecting parrots, toucans, and even eagles, feeding on their rich, protein-laden blood before moving on to its next victim. Unable to defend themselves due to the lack of arms, these birds are helpless as the monstrous bat drains them of blood.
3. Human
WARNING: The video clip above may be considered disturbing by some. Yes, it's true. As a human, you are technically the largest parasitic species on Earth. This is due to the cultural practices of the Masai tribe of Central Africa, who engage in a unique form of parasitism. Rather than becoming full-fledged predators like most of humanity, the Masai cattle herders make an incision into the carotid artery of their cattle, draining several quarts of blood before the precision wound naturally closes. The extracted blood is collected in hollow gourds and mixed with cow's milk, which is then consumed by the herders. Apart from the Vampire bat, this practice makes humans the only mammals known to parasitize another species in this manner.
2. Red-breasted Sapsucker
The Red-breasted Sapsucker is a bird that evokes both admiration and disdain, as it stands as the most stunning yet one of the most destructive parasites on Earth. This distinctive parasite is native to North American woodlands. Unlike other woodpeckers, the Sapsucker creates hundreds of tiny holes in the bark of its host tree, feeding on the continuous sap flow. After several years, the tree succumbs to death, but not before it nurtures an entire family of parasitic birds, which make their nests within the tree. These sap holes also serve as crucial sources of food for hummingbirds and insects, and the resulting dead tree provides valuable habitat for various wildlife. However, in orchards, the presence of sapsuckers can lead to catastrophe, as they invade prized fruit trees, leaving behind hundreds of sap-draining holes that eventually kill the trees.
1. Pearlshell
While a shellfish may seem harmless and innocent, the reality is far more devious. During the breeding season, large freshwater clams, known as Pearlshells, which can grow up to 7 inches in diameter, release thousands of tiny larvae. These minute larvae, called Glochidae, are parasitic and aggressive toward salmon and trout. Weighing only a fraction of a nanogram, the larvae would normally be swept downstream. However, armed with razor-sharp hooks, the Glochidae latch onto the flesh of salmon and trout, attracted by the foot ornamentation of the parent clam as the fish swim upstream. Once the young clams reach the headwaters, they are sufficiently developed and detach from the fish, sinking to the riverbed where they will spend the next 50 to 100 years growing to full size. The damage they inflict on the fish includes painful lesions, but the adult clams, which filter feed, ultimately contribute to the ecosystem by enhancing water quality.
