Posted by: Rob Viens | April 18, 2012

Darwin Pickles Pacman

On April 18th Darwin was still exploring the forest around Socêgo.

“I succeded in collecting many insects & reptiles. — The woods are so thick & matted that I found it quite impossible to leave the path. — the greater number of trees, although so lofty, are not more than from 3 to 4 feet in circumference. These are interspersed with others of a much greater size. — Signor Manuel was making a canoe 70 feet long, & on the ground was left 40 feet, so that there were 110 feet of straight solid trunk. ” (Apr 17/18)

On or about that same day, he came across (and collected) at least one amphibian, too.  In his Zoological Journal Darwin writes:

“Ceratophis: My specimen inhabited the dark & moist forest round Socêgo.— Its habits were those of an English toad, than a Frog. All its motions slow & feeble: proceeded by slow short jumps.” (Zoological Journal)

His spelling may be off, or it may have changed in the last 150 years, but what Darwin is referring to is a frog that belongs to the genus Ceratophrys – the South American horned frogs. There are several species of horned frog found throughout South American and several are endemic  to (i.e., only found in) particular parts of the continent.  For example, there is the Surinam horned frog (Ceratophrys cornuta) and the Venezuelan horned frog (Ceratophrys calcarata). A couple of these species are found in Brazil, including the Brazilian horned frog (Ceratophrys aurita) and the Argentine (sometimes called Ornate) horned frog (Ceratophrus ornate).

Surinam and Argentine horned frogs (from Wikipedia Commons):

Horned frogs

These frogs are also called “wide-mouthed frogs” because of their large mouth that takes up most of their face.  This has led to a much more colorful name for these frogs – Pacman frogs (named after the famous video game character).

Of course, the frogs evolved that wide mouth for a reason – they are top carnivores and eat whatever they can fit in their mouth.  That includes insects, as one might expect, but also fish, mice, reptiles and even other frogs.  They are apparently fearless and very aggressive – attacking any potential food or threat with their big mouth. According to Wikipedia, a fully grown female Argentine horned frog can eat a grown rat!

Although they have some sharp “spikes” in the mouth for holding on to prey (like a steel trap), they have no teeth – so prey is swallowed whole. It is said that horned frogs sometimes are a little overambitious and some have been known to choke on prey that is too large to swallow.

“Pacman” frogs from the Funny Pets blog – this is probably also an Argentine horned frog.

Horned frogs

As with all his specimens, Darwin preserved them to bring back to England in “spirits of wine” – a solution of ethanol. Unfortunately the “spirits” had the effect of leaching the color out of the specimens.  This was true of this poor fellow, too, Darwin notes that already, “colours in the Spirits have become rather fainter.— Iris bright copper colour.”

Tomorrow, in the nearby woods, Darwin pickles four multi-colored ghosts, a Centipede, and a large ape named Donkey Kong. (RJV)

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