Posted by: Rob Viens | May 20, 2012

Darwin and the Shining Ones

Today, May 20th, Darwin spent another leisurely day with his friends, noting:

“Mr Derbyshire, who after leaving the Beagle has remained in the city, paid us a visit. — In the evening Earl (who is nearly well) & we two walked round the Botofogo bay.” (May 20)

I have no doubt, given his interests, that he noticed a beetle or two on the walk about.  So I’ll take this opportunity to wrap up:

Beetle Mania logo

OK – I know it is actually day eight, but one extra day of “Beetle Mania Week! ” seems appropriate. I mean, considering that beetles make up about 20% of all identified species on Earth, one more day only seems fair. Plus, if I am being true to the Beetles, then “Eight Days a Week” is right on target!

Today – an introduction (mostly in Darwin’s own voice) to that most elegant of beetles – the firefly. In the scientific lingo these little lanterns of the night make up the Lampyridae Family.  What a great name –Lampyridae.  It means “shining ones” in Greek, and seems to fit their fairy-like nature.

Firefly species from the eastern US (from Wikipedia Commons)

firefly species

Even Darwin is awed by this beautiful beetle and describes it in far more detail than any other in the “Rio” section of Voyage of the Beagle .  Here are a few of his thoughts:

“In the early part of the night of April & beginning of May. the marshy fields were illuminated by this beautiful insect” (Zoological Notebook)

“At these times the fireflies are seen flitting about from hedge to hedge. On a dark night the light can be seen at about two hundred paces distant. It is remarkable that in all the different kinds of glowworms, shining elaters, and various marine animals (such as the crustacea, medusæ, nereidæ, a coralline of the genus Clytia, and Pyrosoma), which I have observed, the light has been of a well-marked green colour. All the fireflies, which I caught here, belonged to the Lampyridæ (in which family the English glowworm is included), and the greater number of specimens were of Lampyris occidentalis. I found that this insect emitted the most brilliant flashes when irritated: in the intervals, the abdominal rings were obscured. The flash was almost co-instantaneous in the two rings, but it was just perceptible first in the anterior one. The shining matter was fluid and very adhesive: little spots, where the skin had been torn, continued bright with a slight scintillation, whilst the uninjured parts were obscured.” (Voyage of the Beagle)

Fireflies near NYC – a few hours from where I grew up catching them (posted to YouTube by yes18325) –a video doesn’t really do them justice, but if you’ve never seen them it is a start:

Ever the scientists, Darwin experiments on his specimens, too:

“When the insect was decapitated the rings remained uninterruptedly bright, but not so brilliant as before: local irritation with a needle always increased the vividness of the light. The rings in one instance retained their luminous property nearly twenty-four hours after the death of the insect. From these facts it would appear probable, that the animal has only the power of concealing or extinguishing the light for short intervals, and that at other times the display is involuntary.” (Voyage of the Beagle)

Did you also know that glow worms are basically the larvae of fireflies? Darwin also has a few things to say about these guys, too. He even suspected the relationship between the larva and the adult:

“Larva of the above Lampyrus (I suppose) luminous not quite so strong as our glow worm.— I have no descriptions to recognise for certain the female from the larva of Lampyrus. I never however saw the winged ones near to where the apterous ones were crawling” (Zoological Notebook)

Glow worm (from Wikipedia Commons)
glow worm species

Back home in England he has his suspicions confirmed and writes confidently in Voyage:

“On the muddy and wet gravel-walks I found the larvæ of this lampyris in great numbers: they resembled in general form the female of the English glowworm. These larvæ possessed but feeble luminous powers; very differently from their parents, on the slightest touch they feigned death, and ceased to shine; nor did irritation excite any fresh display. I kept several of them alive for some time: their tails are very singular organs, for they act, by a well-fitted contrivance, as suckers or organs of attachment, and likewise as reservoirs for saliva, or some such fluid. I repeatedly fed them on raw meat; and I invariably observed, that every now and then the extremity of the tail was applied to the mouth, and a drop of fluid exuded on the meat, which was then in the act of being consumed. The tail, notwithstanding so much practice, does not seem to be able to find its way to the mouth; at least the neck was always touched first, and apparently as a guide.” (Voyage of the Beagle)

Both fireflies and glow worms glow due to a chemical reaction in a special bioluminescent organ in their abdomen (more on this in a different post).  The adults primarily flash in order to attract mates, while the larvae glow as a warning to predators (they taste pretty bad). Either way, it is truly a sight to see and a wonderful adaptation.

Well, that wraps up “Beetle Mania Week!” for now. I’ve only had time to scratch the surface, but I do hope it was fun.  I know Darwin will come across many more beetles in the coming months, so really, Beetle Mania is just on hold for now :).

One last image to summarize all the beetle families discussed this week:

beetle phylogeny



  1. I miss all the little bits of light I’ve left behind–
    Above all, I wish I’d never been taken away from the Hudson River Valley.

  2. I know – I like the Pacific Northwest, but I do miss the fireflies and thunderstorms (hmm… a theme).

    Great posts on Secret Gardener recently!

  3. […] I don’t think he was ever able to fully answer this question in his lifetime, but we now know a bit more about the chemical reaction that leads to bioluminescence.  Basically it is the result of a chemical reaction that releases energy in the visible spectrum of light.  An organism (a plant, animal, fungi, bacteria – there are all types of bioluminescent organisms) releases the chemical luciferin which reacts with oxygen to release energy.  This reaction would be relatively slow, and not very “bright” if it were not for an enzyme called luciferase. Luciferase acts as a catalyst speeding up the chemical reaction (thereby resulting in more energy released, i.e., a brighter glow).  There are some slight modifications, but this is also the reaction that occurs in fireflies (see Darwin and the Shining Ones). […]

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