South American Cackling Tree Frogs Mistaken for “Singing” Snakes

In forested regions of Central and South America, there lurks a deadly predator: venomous bushmaster pit vipers (genus Lachesis), reaching over 3m in length (almost twice as long as the average S. American man is tall). One species of this snake, L. muta, has long been thought to “sing” by local natives. But now scientists have found evidence that seems to dispel this myth.

Capable of multi-bite attacks and injection of large amounts of venom that can kill a man, the bushmaster’s singing – which sounds like the loud chuckle of a bird – strikes fear into the heart of any native who hears it. It is fitting, then, that their genus name Lachesis refers to one of the Three Fates in Greek mythology who determined the length of the thread of life. In Greek, Lachesis is the second Fate pertaining “to obtain by lot, by fate, or by the will of the gods.”

The Three Fates (Moirai) of Greek Mythology. Image of the Flemish Tapestry, Victoria & Albert Museum, London, by PrioryMan.

The legend of these singing snakes has long been a puzzle to scientists, as snakes are not known to be able to emit such calls. In a recent collaborative effort, scientists have gone a long way to solving this puzzle. Researchers from the Catholic University of Ecuador, the Peruvian Institute of Research of the Amazon, Ecuadorian Museum of Natural Sciences, and Colorado State University, USA, have now discovered that the snakes are actually not at all responsible for the singing.

The study, published in Zookeys last week, analysed DNA sequences, external morphology and advertisement calls of two species of treefrogs, the Canelos treefrog (Ecnomiohyla tuberculosa) and the veined treefrog (Trachycephalus typhonius) in Ecuador and Peru. Setting out to determine their phylogenetic relationships in the region, they found a completely new species of tree frog and have called into question previous taxonomic relationships among these frogs.

Rabb’s fringe-limbed treefrog (Ecnomiohyla rabborum) is one type of marvelous or fringe-limbed treefrog found in Central and South America. They can glide using their webbed hands and feet. Image by Brian Gatwicke.

In describing the advertisement calls of T. typhonius, the authors commented:

“Interestingly, the call of this species is feared by natives in the lower Pastaza basin (Shiwiar, Sapara, Shuar, Achuar people), because it is commonly confused with the “calling” of the bushmaster Lachesis muta (Squamata: Viperidae). This belief is almost certainly incorrect as L. muta cannot vocalize.” (pp. 124).

The researchers measured 14 acoustic parameters of the frogs’ calls, including call duration, note length, and frequency, and describe them as a “cackle of short notes.” They found that the frogs make these calls from tree-holes containing water, where they appear to breed.

It is quite funny imagining natives running for their lives when they hear this call, not knowing that it is actually a harmless tree frog calling for a mate.

Other Fun Facts about Bushmaster Pit Vipers:

  • The bushmaster’s tail ends in a horny spine, which it sometimes vibrates when disturbed. This behaviour has led it to be nicknamed ‘the mute rattlesnake.’
  • They are the longest venomous snake in the New World, growing up to 3 metres long. Large adults can weigh up to 5 kg.  
  • There are three species of bushmaster snakes: L. melanocephala (black-headed bushmaster), L. muta (South American bushmaster) and L. stenophrys (Central American bushmaster).

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