Posted by: Rob Viens | August 24, 2013

A Skunk by Any Other Name…

On August 23rd Darwin also encountered some potentially “hazardous” wildlife.  As you read about his encounter with this South American polecat, keep in mind that our traveling friend still only had one pair of clothes – the same one that was covered in muck.  Imagine how much his companions would have wanted him around camp if this particular observation had gone bad…

“In the morning the rain did not cease, so we started on our return. — In our path we saw a fresh track of a Lion & commenced an unsuccessful chace: the dogs seemed to know what we were about & were not eager to find the beast. —

In these plains a very curious animal, the Zorilla or Skunk, is sufficiently common. — Its habits resemble those of fitchet, but it is larger & the body much thicker in proportion. — Conscious of its power, it roams about the open camp by day & fears neither dogs or men. — if a dog is encouraged to attack one. — the fetid oil, which is ejected makes him instantly very sick & run at the nose. — Clothes once touched are for ever useless. — Every other animal makes room for the Zorilla.” (Aug 23)

(For more on the lion (puma) Darwin was tracking see On Naming the Puma.)

Darwin’s encounter today was actually with a skunk, not a zorrila (though it is possible that the names were more interchangeable in his time).  In particular, it was likely that he encountered a Humboldt’s hog-nosed skunk or possibly a Molnia’s hog-nosed skunk.  These are the only two members of the skunk family (Mephitidae) that are found in southern South America.

Humboldt’s Hog-Nosed Skunk (from Mammalwatching.com)

humboldt hog-nosed skunk

There are actually about a dozen species of skunk, most of which are found in the Americas (where they are also called polecats).  Three of the four genus are found only in the New World – these include the hog-nosed skunks (Genus Conepatus), the hooded and striped skunk (Genus Mephistis) and the spotted skunks (Genus Spilogale).  The fourth genus – the stink badgers (really, I would not make that up) – are found in Indonesia (Genus Mydaus).  How they ended up on the opposite side of the world is a bit of a mystery.

Of course, the most distinguishing characteristic of skunks is their ability to spray a foul-smelling liquid, with extreme accuracy, from their rear end. Muscles around the scent glands allow for these fluids to be excreted with extreme accuracy – easily hitting a target 10 feet (~3 m) away. This “skill” is basically a defensive mechanism against predators who find the smell offensive (or worse yet, get it in their eyes or nose). (Skunks do have to use their defense sparingly though, as they can only spray about 5 times before having to synthesize a new batch of “ammunition” – which can take over a week.)

A skunk’s spray is composed of thiols – organic compounds that contain sulfur and hydrogen.  Although not quite so foul, other thiols include chemicals that make natural gas smell like rotten eggs and those that contribute to human BO. Humans are highly sensitive to thiols (which is why they are a great way to detect natural gas).  In fact, it is said that we can detect them at concentrations of just 10 parts per billion!  Here is what Darwin has to say about that:

“Azara says the smell can be perceived at a league distant; more than once, when entering the harbour of Monte Video, the wind being off shore, we have perceived the odour on board the Beagle.” (Voyage of the Beagle)

Not all thiols smell bad though – for example, some contribute to the smell of coffee and grapefruit.

Humboldt’s Hog-Nosed Skunk (by A. Brehm, 1927)

humboldt hog-nosed skunk

The hog-nosed skunks that Darwin likely encountered are insectivores that like to dig for their supper, and often burrow in the ground.  Their name, not surprisingly, comes from their pig-like nose.

So why is the hog-nosed skunk a creature after Darwin’s own heart (aside from being named after his hero – Humboldt)?  Well – this little critter is an insectivore that uses its “hog-nose” and claws to root out beetles and grubs.  Although Darwin doesn’t use his nose, he has been known to be so obsessed with beetles that he has put them in his mouth (see An Inordinate Fondness for Beetles).

Zorilla (from the Mammal Network)

zorilla

As noted, a true zorilla (Ictonyx striatus) is actually not a true skunk at all but a member of the weasel family. I know for certain that Darwin did not encounter one because zorilla are only found in Africa. They do look very much like skunks, and they also excrete a fowl scented spray as a defense against predators, much like their American skunk friends.  In fact, zorilla are listed on some web sites as the “world’s smelliest animals” (backing up Darwin’s claim that, “every other animal makes room for the Zorilla”).

Is there some form or parallel evolution going on here?  Or has the true evolutionary relationship between zorilla and skunks still not fully understood?  For now, all I can say is “quien sabe?” …  (RJV)

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Categories

%d bloggers like this: