Readers’ wildlife photos

Today reader Robert Lang, who previously sent us photos from Costa Rica, weighs in with some arthropods:
I realize this is close on the heels of my last set of Costa Rica photos I could not resist passing on a few more photos taken much closer to home (in the East Bay area of California), which I similarly hope you and readers might enjoy.
First, we have a dragonfly, a Flame Skimmer (Libellula saturata), which has been hanging around the goldfish pond (a.k.a. the raccoon feeder) for a week or so. Pretty sure this one is a female, because she repeatedly makes passes over the pond, dipping her abdomen in it. (Sadly for her, I expect that the goldfish make short work of the offspring.) What I love about this picture is that the sunlight casts an orange shadow through her wings, looking for all the world like a fossil impression in the rock.
Next, we have a Darkling Beetle (family Tenebrionidae). There are many species; this looks like it might be genus Eleodes (which have fused elytra); I invite further clarification from readers. This was taken in Mitchell Canyon, on the north side of Mount Diablo.


The reason I was in this particular canyon was not for the beetles, though; it was for this next creature, the California Common Scorpion (Paruoctonus silvestrii), which crawls out of its daytime lairs (typically cracks in cliffs and dirt) after sunset. Like many scorpions, it is fluorescent under UV, and while most scorpions fluoresce in the blue-green, this one is a brilliant chartreuse.
They’re tiny (most that I saw were 2-3 cm in total length), but you can spot even the smallest from several feet away; they stand out like a beacon. This one is a bit washed out (and I’m sure the camera is a wee bit confused by the bimodal color distribution), but by turning down the exposure, quite a bit of detail becomes visible. I’ve tweaked the colors of this next one to approximate what it looks like to the human eye.
Why they fluoresce is a bit of a mystery, but a few years ago Animal Behavior published a paper in which the authors suggested that it served the function of aiding light sensitivity by transmuting the dim level of UV from the night sky into green light that their existing photoreceptors could detect.
Since there are noticeable differences in the peak wavelength of fluorescent emission among species, it would be interesting to see if there were corresponding differences mirrored in the peak photoreceptor sensitivity.


  1. rickflick
    Posted June 20, 2016 at 9:27 am | Permalink

    “Why they fluoresce is a bit of a mystery…”.

    The theory proposed sound plausible. Let me get this straight – they are saying the scorpion collect UV from the sky which makes them glow green. The glow is strong enough so they can see prey in front of them. Amazeballs.
    I wonder why they don’t just emit light at the front end, where all the action is?
    I wonder too, if they can store chemically any UV from the daylight hours to be used as a work light after sunset?

    • Gregory Kusnick
      Posted June 20, 2016 at 11:19 am | Permalink

      “The glow is strong enough so they can see prey in front of them.”

      That’s not how I read it. What the paper’s abstract seems to be saying is that the fluorescence tells the scorpion when to run for cover. It’s not meant to illuminate anything, but serves rather as a sort of dashboard warning light that says “You are visible in UV”. As such it allows the scorpion to distinguish between full dark, when it’s safe to roam about, and UV illumination, when it might be less safe.

      • gravelinspector-Aidan
        Posted June 20, 2016 at 2:14 pm | Permalink

        Speaking as someone who routinely keeps a UV lamp in his rig bag to look for scorpions, they don’t seem to be particularly fazed by being “lit up.”

        • Gregory Kusnick
          Posted June 20, 2016 at 2:52 pm | Permalink

          I can neither confirm nor deny their claim, but here’s what they said in the abstract:

          In our experiments, however, scorpions responded most intensely (abrupt bouts of locomotory activity) to 395 nm and 505 nm.

          • gravelinspector-Aidan
            Posted June 20, 2016 at 3:17 pm | Permalink

            Hmmm, well, having been in the position of squatting in the sand dunes of Arabia (the alternative being a mile walk up-dune to the camp, for not much better toilet facilities), I would watch the scorpions scuttering around by the light of the bank-note checker. And the occasional camel spider stalking me. It’s always disconcerting to realise that an invertebrate sees you in the class “lunch”.
            Maybe different species ; maybe different wavelength ; maybe they were pulsing the light abruptly on (while mine would grow in intensity as I approached, then decline slowly). There are lots of possible confounding factors.
            Quick question (answered from Wikipedia) – are there more species of “scorpions” (about 1750 described species)than “mammals”(5,416 species were known in 2006). But even so, that’s enough phylogenetic room for lots of behavioural variation.

  2. Mark Sturtevant
    Posted June 20, 2016 at 9:49 am | Permalink

    Amazeballs, indeed. The beetle does look like Eleodes.

    I had read that daddy-long-legs also fluoresce under UV light, and so you might want to try that out.

  3. Posted June 20, 2016 at 9:50 am | Permalink

    Wait — is there UV light coming from the night sky?

    As far as why scorpions fluoresce — maybe they just do, for no adaptive reason. My teeth fluoresce. My pallid wintertime skin fluoresces (but my tanned summertime skin does not).

    Going through my little cabinet of natural curiosities, I find that bones fluoresce weakly, teeth moreso, and porcupine quills fluoresce just as brightly as my scorpion preserved in lucite.

    • rickflick
      Posted June 20, 2016 at 10:50 am | Permalink

      I hope your collection will be open to the public soon. It would make quite an attraction.

      • Peter N
        Posted June 20, 2016 at 11:02 am | Permalink

        You can drop in any time!

    • Mark Sturtevant
      Posted June 20, 2016 at 11:23 am | Permalink

      I am also inclined expect that the fluorescence thing is pretty much an accident. A happenstance effect of a peptide or lipid in the cuticle of these animals.

      But I would be happy to be wrong. Many animals can see into the UV, and they use it for a variety of purposes. Perhaps if they recognize a UV-reflective object they think ‘oh, that is something I might eat or mate with’.

      • Gregory Kusnick
        Posted June 20, 2016 at 11:31 am | Permalink

        The authors note that the wavelength emitted by the fluorescence coincides with the peak sensitivity of the scorpion’s eye. That coincidence make sense if it’s adaptive, not so much if it’s just an accident.

  4. Posted June 20, 2016 at 9:58 am | Permalink

    We are still awaking to the facts of UV genes on behaviour. Thank you for keeping things honest and scientific!

  5. Posted June 20, 2016 at 11:08 am | Permalink

    I did not know there were beetles with fused elytra! Thanks for the info, and nice photos.

  6. Mark R.
    Posted June 20, 2016 at 11:11 am | Permalink

    That is a great Flame Skimmer capture. Kudos.

    One of my earliest memories was seeing scorpions at Alum Rock by San Jose, CA. I must have been 4 or 5. I’m sure they were the same species, though I never knew until now that they fluoresce; to echo what others already said- amazeballs!

  7. darrelle
    Posted June 20, 2016 at 12:53 pm | Permalink

    That Flame Skimmer pic is indeed very nice.

    Very interesting that the fluorescent emissions of the scorpion happen to fall into a range that the scorpion’s eye is good at detecting. Or, are these emissions within a range that is common of UV absorption bio-fluorescence?

    • Gregory Kusnick
      Posted June 20, 2016 at 3:05 pm | Permalink

      Fluorescence is the absorption of a short-wavelength photon followed by the emission of a longer wavelength photon. Since the next longer wave band from UV is visible, UV fluorescence pretty much always produces visible light.

      So that accounts for the fact that it’s in a range that the scorpions can see. But if it further turns out to be finely tuned to match the peak sensitivity of the scorpion’s vision, that’s probably not just happenstance.

      • darrelle
        Posted June 21, 2016 at 6:52 am | Permalink

        I agree that it is interesting, but I have doubts. Perhaps the coincidence is a result of adaptation but the hypotheses suggested to explain it are not convincing to me as of yet. For example, the spectrum of sunlight at the Earth’s surface is significantly stronger at 505 nm than at any UV range including 395 nm. After looking a bit I couldn’t find any conditions, sunrise, sunset, direct sun, cloudy conditions, etc. for which that isn’t the case.

        Given that there doesn’t seem to be an advantage to see UVA light transduced to green light when the spectrum available is already significantly stronger in green light than in UVA. Unless there is some advantage to detecting UV specifically rather than just as a source of illumination?

        Even more interesting to me than the eyes are the photosensitive elements in the scorpions tail that are sensitive to green light and the hypothesis that perhaps the scorpion’s entire body is used as a photon collector.

  8. John Harshman
    Posted June 20, 2016 at 2:34 pm | Permalink

    Beautiful flame skimmer and great colored shadow. However, I’m pretty sure that it’s a male. Females are brown.

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