Today's "everything you ever wanted to know about..." is dedicated to the flying snake, a strange creature that has many different appearances, and whose myth is spread all over Chile.
First references to a Flying Snake
Luis de Valdivia, wrote the first Mapuche Language Grammar book and dictionary in 1684, though he does not mention the piwichen [*], he has an entry for “culebra” or non-venomous snake under “bilu” and another for “serpent” as “yhuai”.
[*] Like most words of a non-written language, each author chose his own phonetic system to write them. As we can see below, the name is spelt in a similar, but at the same time different manner by each of the sources that I have used in this post:
In 1765, Father Andrés Febrés, wrote another “Grammar” in which we can find the first printed references to the flying snake, the 1846 edition that I have read, has the following entries:
SERPENT: Vilú: another they say it flies, pihuchen.Rodolfo Lenz, in his Estudios Araucanos, states that Febrés original edition (1765) called the creature pimuychen and wrote that it was “a snake that they say flies when it hisses, and he who sees it, dies”.
[Non-poisonous] SNAKE: Vilu: that they say flies and hisses, pihuchen. 
In the later edition, quoted above, Hernández corrected the entry and changed the name to pihuchen.
Another missionary, Havestadt, is cited by Lenz  ; he wrote a Grammar dated 1777, in Latin, and repeated Febrés entry but called the animal pihuichen:
pihuichen, coluber, angujs, serpens volatilis, quem quie videt, vel audit sibilare, moritur: addo et qui non videt; uti visus est nemini
Snake or mammal?
In the early 1800s the first Chilean naturalist, father Molina in his treaty on the Natural history of Chile, mentioned it in a biological context as follows:
Piguchén, four footed winged or species of great bat, which -if its existence were real- would form one of the links that join birds and mammals. This animal, according to what they say, has the body and size of a domestic rabbit and is covered with a fine cinnamon colored fur: it has a pointed muzzle, large eyes round and shiny, ears barely visible, membranous wings, short five toed legs, a tail that starts round and is then long, similar to that of fish; it hisses like the snakes and flies like a partridge; it lives in the hollows of the trees, which it only leaves at night; it does no harm, only to insects, which it eats. 
Molina’s description is quite unlike the previous ones: this is not a flying snake, it is a hairy, four footed beast. Some kind of long tailed bat. A harmless night creature.
The myth, like most Mapuche traditions extended with their language across the Andes into northern Patagonia, where the Puelche people spread it across the Pampas.
The Puelche were a group of Northern Tehuelche natives (also known as “Pampas”) that adopted the Mapuche language and became “Araucanized” in the mid 1700s.
At the military frontier with the Puelche, Argentine commander, Federico Barbará recorded a Puelche vocabulary, and published it in his 1879 dictionary. He mentions the beast as a Flying snake: Pinuychen and included a footnote that echoes Febrés comment:
The Indians say that he who sees this snake when it flies, falls dead: that is why, when they see it coming, they take off or throw themselves on the ground face down. Despite their explanation, it does not exist. It is a legend of the machis (witches). 
Father Augusta: a Vampire
In 1916, Father Félix de Augusta included the following entry in his Spanish-Mapuche dictionary:
piwichen. Probabl[y] comp[osed] of piwn and ché imaginary animal which is described as follows “Its body has the shape of a elongated cylinder, like a snake. As time goes by, it grows wings and flies, but it lacks feathers. It sucks the blood of people and animals drying the body of its victims. Its hissing, that sounds ‘piurüt piurüt’ announces a sure death if the person that is being approached by the perverse creature does not have a chance to see it before being seen by it. When it infests a house, all of its residents will have to die, their only means of escape is to move to the other side of a stream. There are some who pretend to have caught it in a bowl with wine. It also has an important role in the visions and superstitions of the macis”. It is believed that the vampire bat, that exists in Chile may have originated the myth. – Death of cattle is attributed to it. 
To clarify the origin of the name, his entry for piwun is to dry, to parch. While ché is person. So this creature’s name means: “to dry, to parch a person”, surely from its habit of sucking its victims dry.
According to Augusta it is a vampire-like winged snake.
The real vampire (Desmodus rotundus) a bat which feeds on the blood it sucks from cattle, is found all over South America, including Chile but this creature is too small to be the rabbit-sized Piguchén as it is barely 10 cm (4 in.) long and weighs not more than 50 g (1.8 ounces); it also lacks a tail.
Latcham. Also a vampire.
Latcham (1924) mentions the myth  as the “most common [myth] among the Chilean peasants, it is a fabulous animal, whose shape changes from region to region. This myth is known all across Chile, it is very ancient and of undoubted Indian origin”.
But is it a Mapuche myth? I does not seem so. Mapuche people did not live in northern Chile.
He adds that the piguchén is depicted as a “ feathered culebrón [big snake], sometimes with wings, mostly without. Frequently it lacks feathers and in those cases it carries a row of bristles along its back”.
But most frequently it is depicted as a winged snake (with or without feathers). A blood sucking vampire.
Vicuña Cifuentes. Bird features
Vicuña Cifuentes, in his 1915 book on Chilean myths recorded this creature as being spread throughout Chile: 
At Talagante (in the metropolitan area of Santiago, Chile's capital city) “it is a snake that after a certain period of time, transformed itself into a kind of big sized frog, covered with very fine and short hair with short and wide wings that let it take short flights”.
At Melipilla (also by Santiago) it is a snake that when it grows old turns into a bird the size of a young turkey. It hides in the trees during the day and its red excrement can be seen on the tree trunks.
At Coinco (34°16’S, 70°57’W) it is a “bird the size of a hen whose head ends in a long and thin beak, its eyes are big and of a very pale grey color, it has very small wings, almost rudimentary and rough and strong bristles along its spine” it sucks the blood of mules.
At Vichuquén (112 km - 70 mi. west of Coinco) it is a snake with wings “perfectly covered with feathers”.
In my opinion, a feathered flying creature is a bird. Feathers spell bird. Flying if feathered is a bird. So the myth points at a bird.
Guevara. Vampire but bird-like.
Tomás Guevara,  noted in 1908 its blood thirsty qualities:
on the days of great heat it sticks to the tree’s bark and leaves there a track of blood.
After repeating the see it and die myth and its vampire features, he mentions that “ in its old age it turns into a bird the size of a cock, that causes the same damages as it did in its original shape”.
He also mentions it in the region of Ovalle (1904) close to the cities of Coquimbo and –La Serena: “ Piuchén has the wings and beak of a parrot, the body like a toad and the tail of a big snake.”
Vicuña Cifuentes quotes Guevara (History, I, 231): “Pihuichen was also recognized by the ancient indians , it represents another shady and fearful monster, shaped like a winged snake .”
So it seems to be an old pre-hispanic myth.
Ricardo Latcham in 1923 wrote that “it is a hybrid […] frequently a bird the size of a chickenbut always with some particularity that distinguishes it from the other birds, like bat wings, bristles along it spine, etc.”. 
He adds that at Coquimbo (northern Chile) the farmers make it out as a “winged snake with a head at each tip” motif which he notes is found in the ancient pottery found in the area. 
See my entry on the Culebrón which also mentions a big (though non-flying) snake that was found in the Diaguita native’s culture.
Latcham noted that despite the different representations of the beast, all agreed on the fact that it feeds by sucking human or animal blood.
Latcham and a merging of the Culebrón and Piwichén myths
Latcham wrote that despite the fact that its most common name is piguchén, which is written in many different ways,
it is nevertheless known in some places with another name. That is why in the northern provinces it is known as culebrón; in Chiloé it is called chiued or raiquén.
Cavada,  calls it Puchén or Piguchén. mentions it in Chiloé as follows:
The meaning of that word [Piuchén] in Chiloé is that of a metamorphosis or phisical degeneration of a being […] that is why when a red cock lays a small egg from which the Basilisk is born, it remains Piguchén , a new and strange being […] all Piguchén reach an extraordinary longevity and some never die like a phoenix.
Discussion. Piwichen is not a Patagonian myth.
However, I tend to disagree with Latcham, because, as Cavada notes, the meaning of the word Piguchén in Chiloé is different. It does not refer to a flying snake but to a bizarre or odd event. Furthermore, the raiquén is a bird (most likely an owl) not a bat or a flying snake.
Perhaps the Flying snake myth originated in the northern Andean cultures (i.e. Inca, or even in the Western Argentine natives such as the Diaguita) and was adopted in Northern and Central Chile before (or after) the Inca occupation of Chile (1450-1540). The Mapuche at their northernmost reaches may have been in contact with this myth, and took it south into the Arauco region during the Spanish conquest, while they retreated and entrenched there.
It permeated in a deformed manner south into Chiloé island and into the Pampas as we can see in the following map:
In the map above, you can see the homeland of the Mapuche (in Chile which is centered around Santiago, Chile) and the area which the "Araucanized" Puelche, Pehuenche, Huilliche groups occupied from Mar del Plata on the Atlantic, to Chiloé Island in southern Chile.
The Inca empire is shown in green.
It can be clearly seen that at the area where Mapuche homeland and Inca empire overlap, is the where the "flying snake" myth is most mentioned.
The only two outstanding "points" on the map (one in the Pampas a myth imported by the Puelche from Chile and the other in Chiloé where it has a completely different meaning) are quite distant from the point of origin of the myth (around Santiago) and from other non-Mapuche areas (Coquimbo and Ovalle) closer to the source of the myth either in the Inca empire or the land of the Diaguita (around Tucumán and Salta).
See my next post on the possible Inca origin of Chile's "snake" myths .
Summary: One thing is for sure it is not an aquatic reptile and therefore cannot be used to explain cryptids like Nahuelito.
In my opinion it does not refer to any Patagonian lake monster or cryptid it is a myth referring to a bird.
 Valdivia, Luis de, (1684). Arte y gramatica general de la lengua que corre en todo el Reyno de Chile. Sevilla : Thomás López de Haro.
 Febrés, Andrés (1846). Revised by Antonio Hernández, Santiago Impr. del Progreso, 1846 pp 25 and 93.
 Lenz, R. Op. Cit. pp. 436
 Molina. Op. Cit. pp. 264
 Barbará F., Op. Cit. pp. 56
 Augusta, F. Op. Cit. pp.184.
 Guevara, T., (1908). Psicolojía del Pueblo Araucano. Impr. Cervantes. pp. 321-322.
 Vicuñ Cifuentes, J, (1915) Op. Cit. pp. 80-82 and 339.
 Latcham, R., (1923). La Historia Natural en los mitos Araucanos . Revista Chilena de Historia Natural. v.27. pp. 132. Online:
 Latcham, R. Op. Cit. (1924). pp. 571-573.
 Cavada, F., (1914). Chiloé y los Chilotes. Impr. Universitaria. pp. 102-103.
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia
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