Existence

It clings to your mind

Like a phantasmal leech

Nesting itself deep within

The substance of your soul

Demanding every second

Of your prying attention

In the continual search

For the methods to reveal

The ultimate secrets

Of existence

Infests in your blood

It's magnificent seed

Preparing the symbiose union

It feeds you to grow

It crawls along the surface

Of your reality's cocoon

Impatiently awaiting

The miracle of birth

The parasite completes its cyclus of life

Cymothoa exigua, or the tongue-eating louse, is a parasitic crustacean of the family Cymothoidae. This parasite enters fish through the gills, and then attaches itself at the base of the fish's tongue. The female attaches to the tongue and the male attaches on the gill arches beneath and behind the female. Females are 8–29 millimetres (0.3–1.1 in) long and 4–14 mm (0.16–0.55 in) in maximum width. Males are approximately 7.5–15 mm (0.3–0.6 in) long and 3–7 mm (0.12–0.28 in) wide.The parasite destroys the fish's tongue, and then attaches itself to the stub of what was once its tongue and becomes the fish's new tongue.

Cymothoa exigua extracts blood through the claws on its front, causing the tongue to atrophy from lack of blood. The parasite then replaces the fish's tongue by attaching its own body to the muscles of the tongue stub. The fish is able to use the parasite just like a normal tongue. It appears that the parasite does not cause any other damage to the host fish.Once C. exigua replaces the tongue, some feed on the host's blood and many others feed on fish mucus. This is the only known case of a parasite functionally replacing a host organ.There are many species of Cymothoa,but only C. exigua is known to consume and replace its host's tongue.

Not much is known about the life cycle of C. exigua. It exhibits sexual reproduction. It is likely that juveniles first attach to the gills of a fish and become males. As they mature, they become females, with mating likely occurring on the gills. If there is no female present, within a pair of two males, one male can turn into a female(!) after it grows to 10mm in length.The female then makes its way to the fish's mouth where it uses its front claws to attach to the fish’s tongue.

Cymothoa exigua is quite widespread. It can be found from the Gulf of California south to north of the Gulf of Guayaquil, Ecuador. Two host records were also recently discovered in Costa Rica.

It is currently believed that C. exigua are not harmful to humans unless picked up alive, in which case they can bite.

(source:Wikipedia)

When i first heard the song Existence, the opening track of Thorns masterful debut album, i thought that it had to do with the alien from the Alien films.However, according to Snorre W Ruch, the guitarist, main composer and mainman of Thorns the song's lyrics speak about humanity..But apart from the human parasite, you have to agree that Cymothoa exigua was far too awesome to be ignored  when talking about parasites, right?

The album Thorns was released in 2001 and it's the debut album(and the only album up to this day) of the homonymous one-man band.
It is also one of the best metal albums ever regardless of subgenres, an avant-garde masterpiece and the 
pinnacle of the Moonfog sound that dominated(artistically,not commercially) black metal in the late 90's/early 00's.

                                                                         Nesting itself deep within