Posted by: Rob Viens | July 2, 2012

Darwin Goes “Crackers”

On July 2nd Darwin made the rounds – saying goodbye to some of the friends he’d met in Rio:

“Walked to Botofogo & called on the Admiral, Mr Aston & Mr Price.— The latter I hope we shall again see at Valparaiso: He is afraid 17 years in Chili has quite unfitted him for any other country, & now on his road, he is sorry he ever attempted the change.— It will make Valparaiso very pleasant if we are lucky enough to find him there.” (July 2)

See The Doctor, the Admiral, and the Naturalist and Who’s Who Guide to 19th Century European Diplomats for more on Admiral Thomas Baker and Arthur Aston. Mr. Price, I’m afraid, has been lost to history (at least to me). But he lives on in Darwin’s diary.

In his Zoological Notebook and later in Voyage of the Beagle, Darwin also talks about encountering a “noisy” butterfly, which he identifies as Papilio feronia.

“I was much surprised at the habits of Papilio feronia. This butterfly is not uncommon, and generally frequents the orange-groves. Although a high flier, yet it very frequently alights on the trunks of trees. On these occasions its head is invariably placed downwards; and its wings are expanded in a horizontal plane, instead of being folded vertically, as is commonly the case. This is the only butterfly which I have ever seen, that uses its legs for running. Not being aware of this fact, the insect, more than once, as I cautiously approached with my forceps, shuffled on one side just as the instrument was on the point of closing, and thus escaped. But a far more singular fact is the power which this species possesses of making a noise. Several times when a pair, probably male and female, were chasing each other in an irregular course, they passed within a few yards of me; and I distinctly heard a clicking noise, similar to that produced by a toothed wheel passing under a spring catch. The noise was continued at short intervals, and could be distinguished at about twenty yards’ distance: I am certain there is no error in the observation.” (Voyage of the Beagle)

Darwin’s Papilio Feronia (1833) – called Ageronia Feronia in 1889 by Robert Taylor Pritchett in this image from 1890:

Hamadryas feronia

Sometime in the last 100 years this little butterfly was renamed again and now goes by the name Hamadryas feronia – the Variable Cracker (shown below in an image from Wikipedia):

Hamadryas feronia

Whatever the Latin name might be, Darwin’s butterfly belongs to an interesting genus commonly known as “Cracker Butterflies”.  Why “Cracker”?  Well that name comes from the interesting characteristic of the genus described again here by Darwin:

“Strange as it may sound, they when fluttering about emitted a noise somewhat similar to cocking a small pistol; a sort of a click.— I observed it repeatedly.” (Zoological Notebook)

This sound, made by both sexes, seems to be used for defending territory, warning others of predators, and attracting or courting mates. This is consistent with Darwin’s description of butterflies chasing one another while making the sound.

Interestingly, although the sound mechanism is known to be found on the wings, it is not entirely clear how the butterflies make the clacking sound (though there are several hypotheses).  Sources suggest it is ” percussive, not stridulatory”, i.e., a percussion sound (say like a drum or clicker) rather than a sound made by rubbing two parts together (like a violin string). The most recent papers (I can find online) say it is made by enlarged veins on each of the wings that are “clapped” together.

It is surprising hard to find good footage of a cracker butterfly, but he is one that is not bad and which shows several species (or different sexes of the same species):

I assume the sound they make is too low to capture on a recording, as no one (that could find) has posted a recording of the “cracker” sound that Darwin describes and which give this particular butterfly its name.

Some other interesting info about Crackers:

  • Seeing as they can use sounds, it makes sense that Hamadryas also has the ability to hear – they have ears (which is not quite as common in the butterfly world as one would think).
  •  They primarily use camouflage as a form of defense. Here is a Hamadryas februa resting on a tree (from butterflycorner.net).
    Hamadryas februa
  • Hamadryas have a symbiotic relationship with plants of the Euphorbia genus (spurges).  This is the only plant that they will lay their eggs on – the type of food the young caterpillars eat.

Red Cracker (Hamadryas amphinome) (from the Florida Museum of Natural History)

Hamadryas amphinome
The Florida Museum of Natural History has a beautiful Butterfly Identification Guide – be sure to check out the colorful images.

Starry Night Cracker (Hamadryas laodamia) (from the Florida Museum of Natural History)

Hamadryas laodamia

Interestingly, this species is the only Hamadryas that does not make a sound.  A recent paper suggests that it had the ability but lost it due to a more recent adaptation. Evolution is so cool!

Darwin was surely having a cracking good time! Yeah, I said it… (RJV)

PS – For more on Darwin’s encounters with forest musicians, be sure to see Eine kleine Nachtmusik in the Forest.

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