Francisco de Amaral Varella's Minhocão on the Rio das Caveiras

The campos of southern Brazil had a monster. Locals called it the Minhocão. A gigantic subterraneous animal, said to tear up the ground, uproot mighty pine trees and divert the courses of streams. Most of the stories were wild. Some made it as big as a house, 60 metres long.

In March 1877 the German naturalist Fritz Müller wrote from Blumenau to Charles Darwin. He had collected Minhocão accounts on an excursion to the Campos dos Curitibanos. Most, he said, were "truly fabulous". Yet he thought it "highly probable, that some very large animal (about 1 mètre in diameter)" lived in the large swamps along tributaries of the Uruguay and Paraná.

One account stood apart. Around 1870, Francisco de Amaral Varella was about ten kilometres from the town of Lages, in Santa Catarina. On the bank of the Rio das Caveiras, he saw "a strange animal of gigantic size, nearly one metre in thickness, not very long, and with a snout like a pig." Whether it had legs or not, he could not tell.

He called his neighbours to his assistance. By the time they came, it had vanished. It did not go without "leaving palpable marks behind it in the shape of a trench". Later retellings say it lumbered off and disappeared into the ground. Eberhart's entry puts the trench in swampy ground.

A few weeks later, a similar trench was found nearly 4 miles away, on the opposite side of Lages. A party of locals followed it. The track led under the roots of a large pine tree. Then it was lost in swampy ground.

The information came from Friedrich Kelling, a German merchant then living in Lages. He saw the trenches himself. George M. Eberhart's encyclopedia counts him as a second witness to the animal. The older wording says only that he saw the trenches.

Müller published "Der Minhocão" in Der Zoologische Garten in 1877. On 21 February 1878, Nature carried an English summary titled "A New Underground Monster". Scientific American Supplement reprinted it that May. In May 1878 Müller reportedly claimed he would bring a dead specimen to Europe. None ever arrived.

Müller had his own answer. A giant cousin of Lepidosiren and Ceratodus, the lungfish, living hidden in the swamps. Other nineteenth century naturalists, struck by the armadillo-like scales of folklore, wondered about a surviving glyptodont. Richard Burton was sceptical and linked the stories to riverbank erosion. Others noted trenches that appeared after heavy rain, with a rumbling sound like thunder, and suggested seismic activity.

Karl Shuker proposed a giant caecilian. These are limbless, burrowing amphibians with head tentacles, which might explain the horns of other Minhocão tales. Shuker also gave the date of about 1870 that most modern accounts follow.

Bernard Heuvelmans included the Minhocão in On the Track of Unknown Animals in 1958. Shuker, Eberhart and Brent Swancer kept it alive for new readers. Of all the stories Müller gathered, Varella's account remains the clearest. One man. One strange animal on a riverbank. And a trench in the earth where it had been.