Rich in all kinds of animal life as is Paraguay, the average inhabitant or traveller sees but few specimens. Perhaps there is no country in the world where the wild game is so shy, or where its natural haunts are so impenetrable. Curious and fearful indeed are some of these rare animals, according to the stories told by the Indians and Paraguayans of the more remote parts.
     Perhaps the most celebrated of these creatures is the "Mboya Jagwa," or dog-snake, a huge water-serpeant which is said to attain a length of from 60 to 100 feet. So far this monster is unknown to science, though one white man now living in Paraguay is said to have discovered a huge skeleton on the banks of a Riacho in the Choco; unfornately, he did not realise the value of his find, and took no steps to preserve this interesting trophy. The Indians describe the creature as having a head like a dog, and as carrying that similarity still further by yelping like a puppy.
     I have heard the story of an Indian who was attacked by one in crossing a little river in the central (arid quite populated) part of Paraguay. The serpeant swam swiftly towards the frightened man, and swirling in the water attempted to envelop his victim in the coils of his tail. The old man escaped this fate only by diving and escaping to the shore.
     All the Indians, the Paraguayans, and the Correntinos of the North of Argentina vouch for the existence of this horrible animal, and agree down to the smallest details in their descriptions of the creature and its habits. I have known an Indian village to be moved to another part of the country on account of the terror inspired by an "Mboya Jagwa" which had taken up its abode at the river crossing in front of their "toldos."
     In the Cordilleras, stretching from Villa Rica to the Rio Parand, people describe a probably extinct monster called the Tiger Jaguar (Iguana-Dog)—a creature with the head and tail of an alligator and the body of a dog. Now, these people have never had access to words of geology, so cannot know that they are giving a fairly accurate description of the "Dinosaurus," which existed in Colorado and Nebraska in immense numbers during other geological periods. If the animal is really extinct—although all sorts of things might be found in the forest-clad fiills of this range of mountains—it is evident on the face of things that the tradition has been carried down from father to son from a period during which the terror actually did exist.
     The natives of these parts also believe in the old myth of a huge dragon being chained up in a cavern in the hills. Indeed, fantastic legends are so interwoven with the life and speech of these primitive people that it is hard to know where to allow scepticism to yield to credence. Yet the fact remains that strange, untoward animals and reptiles do exist in the savage parts of Paraguay, and of these it is not at all improbable that some may have so far escaped scientific observation.

This article was taken directly from Alexander K. Macdonald's (1911) Picturesque Paraguay, sport, pioneering, travel: a land of promise, stock-raising, plantation industries, forest products, commercial possibilities.

Anne, S. Peck's (1913) The South American Tour also mentions the legendary snake:

With some poor land there is more with rich vegetation, immense forests, wild animals of many kinds, including boa constrictors. And there is a tale of a creature called Mboya Jagwa, dog snake, a water serpent unknown to science, 60 or 70 feet long with a head like a dog and a hooked tail. The Indians all agree in their description of it, and one village moved to another part of the country because one of these creatures had settled near by.

Australian interest in Paraguay was stimulated by the formation of a Utopian society by the New Australia Movement.

Paraguayan Barking Snake

Dubious SNAKE of South America.

Variant name: Mboi-yagua (“tiger snake”), probably Guaraní (Tupí), although alleged to be Paraguayan Spanish (yagua comes close to the Spanish yaguar, “jaguar”).

Physical description: Length, 10 feet. Doglike head. Swollen abdomen. Four needle-sharp hooks on its tail.

Behavior: Barks like a dog.

Distribution: Upper Río Parana, Paraguay.

Significant sighting: In February 1972, government surveyors brought a specimen of this snake from the jungle to the Botanical and Zoological Garden in Asuncion, where it was kept.

Probable explanation: Journalistic misunderstanding and mistranslation of the term Mboiyagua as “dog snake” instead of “tiger snake,” the Guaraní Indian name for the Anaconda (Eunectes murinus). The specimen caught was pregnant, hence the swollen abdomen.

Sources: “The Paraguayan Monster,” Pursuit,

20 (October 1972): 86–87; “The

Curiosity for the Australian Utopia landed me by the side of the great east-west road, Ruta Dos, at the dead of night. The bus dropped me at the sign for the Nueva Londres.

‘It’s up there,’ said the driver. ‘Eleven kilometres.’

Up where? The road leached away into the darkness. There was a mercanta hurriedly packing up her stall.

‘No,’ she said, ‘there are no hotels, no taxis, no buses. At this time, the only people out on the ruta dos are bad ones.’

Faced with conspicuously bleak options, I shouldered my pack and groped my way towards the junction. I stepped into the black. I could just feel the camber of the road beneath my feet – so at least I could distinguish forward from ditchwards. These were grasslands. I could tell by the seething of the straw. There were frogs, too, chuckling and sucking and (I soon decided) groaning in horror. Nightjars added their own texture to my burgeoning apprehension. The locals described the noise (aptly I now realised) as the dying screams of the Old Lady of the forest. Then, the last streaks of light from Ruta Dos flickered out, depriving me of every sense except hearing and, of course, terror.

Robbers, snakes, rabid dogs and wounded jaguars contributed the outlines of my anxieties. Paraguayan mythology contributed some unnecessary embellishments. This was not the time to be thinking of the mboya-jagwa, the huge dog-snake that eats travellers, ravishes women and yelps like a puppy. Or the carbuncalo, a revolting carnivorous hog that disguises itself as a trough to engulf the unwary drinker. To the Australian settlers of 1893, these creatures all seemed real enough. Macdonald added to the list with a bird that shone in the dark, a giant bi-sexual ant-bear and a sabre-toothed sheep of uncommon ferocity named – a little ineptly perhaps – the ow-ow.

At The Tomb Of The Inflatable Pig: Travels through Paraguay