Posted by: Rob Viens | December 7, 2012

“Snowing Butterflies” in San Blas

December 4th was a day for stories as the crew of the Beagle shared their recent adventures with the men from the schooners.  Although we hear the about the day as experienced through Darwin’s eyes, I’m sure similar stories were being swapped between crewmen at all “social” levels on the ship.  Darwin notes:

“We ran down alongside the Schooners; & all the necessary business between them & the Beagle was carried on with the greatest activity:— The morning passed away most merrily in hearing & relating everything which has happened since we parted.— The coast, however, on which the Schooners have been employed seems to be even more uninteresting than that of Bahia Blanca.” (Dec 4)

Plans were also made for the next leg of the journey, in which the schooners (and their tiny crew) would be left behind to survey the coast for several months, while Darwin and the main crew traveled south to Tierra del Fuego and the Falkland Islands:

“The instructions for the next three months are as follows:— Mr Wickham, after cauking La Lievrè at R. Negro, runs up B. Blanca; returns immediately & joins Mr Stokes, who will be employed in this neighbourhead.— They then in company sail for Port Desire; & from that point, these little vessels will survey the coast up to Rio Negro.— The Beagle will meet them there in March; which month being very boisterous, our whole fleet intend lying snug in the river.— All the Officers dined together in the Gun-room; soon after which the Beagle made sail.— We are now with a rattling breeze & a bright moon scudding for Nassau Bay, behind Cape Horn.” (Dec 4)

This time it would be almost four months before Darwin knew the fate of his friends on the tiny survey boats.

December 4th was also the occasion for another set of visitors on the Beagle. More specifically, I should say millions of visitors – a huge swarm of butterflies.  In his Zoological Notebook Darwin poetically describes the visit:

“About 10 miles off the Bay of San Blas, in the evening, the infinite numbers of Lepidoptera formed a most curious spectacle: They were of various species, but chiefly a yellow sort.— with them were some moths & Hymenoptera.— & even a Calosoma [?] flew with on board.— The men all cried out “it is snowing butterflies”; at a distance it had this appearance.— the butterflies were in bands or flocks of countless myriads, & as far as the telescope reached, they might be seen fluttering over the water.— This took place in the evening.— the morning had been calm & the day before very light variable winds.— it is clear these insects had voluntarily come out to sea.— it was the last day for most of them, for a strong breeze sprung up from the North, which must have destroyed the greater number.— How are we to account for these flights, which others have also observed? Is it an instinct implanted in the animal to find new countries, its own one being overstocked by a particularly favourable year.” (Zoological Notebook)

This is another great example of how Darwin could appreciate the sheer beauty and wonder of nature while still thinking about “why” the butterflies were behaving they way they did.  To me, this is one of the true skills of a naturalist – blending the art and beauty of the natural world with its scientific foundation. (It seems that many butterflies that swarm do so as a form of migration – usually as a result of a climatic (or seasonal) change such as drought.)

Notes by Darwin, and others who analyzed his descriptions after his return to England, suggest that these butterflies belonged to the genus Colias – also known as the “clouded yellows” or “sulfurs”. One source specifically suggests they were representatives of the species Colias lesbia.

Colias lesbia vauthierii – a subspecies found in Argentina (from Butterflies of the Americas)

Colias lesbia vauthierii

Another Peruvian subspecies (shown below) is Colias lesbia meieri (from the Learn About Butterflies Sit by Adrian Hoskins)

Colias lesbia meieri

The event was so spectacular that even FitzRoy noted it in his Narratives:

“At about four the weather was very hot, the sky cloudless, and varying flaws of wind drove quantities of gossamer, and numbers of insects off from the land. The horizon was strangely distorted by refraction, and I anticipated some violent change. Suddenly myriads of white butterflies surrounded the ship, in such multitudes, that the men exclaimed, “it is snowing butterflies.” They were driven before a gust from the north-west, which soon increased to a double-reefed topsail breeze, and were as numerous as flakes of snow in the thickest shower. The space they occupied could not have been less than two hundred yards in height, a mile in width, and several miles in length.” (Narratives, FitzRoy)

Notice that FitzRoy called them “white” butterflies – more fitting to the “snow” metaphor used by the crew.  Several of the species of Colias are  white in color, it is possible that both varieties were present that day.

In any case, it is a perfect image for a cold December day…(RJV)


  1. I want to see this spectacle!!! Butterflies on parade: “…could not have been less than two hundred yards in height, a mile in width, and several miles in length.” Ah, the awe and beauty of nature…

  2. Hi,Rob,
    I’ve just nominated you Blog of the year 2012 award-for I’ve enjoyed reading your interesting posts trough the year (I am happy the journey still lasts 😉 )
    Please visit my site for details!

  3. Tamara – Thank you so much for the honor, I am very touched to be nominated. I agree with you in terms of what to make of these awards. But what is really meaningful is that this award comes from you – someone who’s blog I enjoy reading and have a lot of respect for. You certainly deserved the honor yourself. I’ve really enjoyed being part of the global community that “being a blogger” creates. Thanks so much!

    Beagle Project Readers – Please check out My Botanical Garden for some great reading. I love the way Tamara connects science, art, history and travel with the vast global garden we all live in.

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