Luminous Beauty: The Secret World of Fluorescent Arthropods

[tripsis]

Luminous Beauty: The Secret World of Fluorescent Arthropods

By Gwen Pearson 11.20.13 10:12 AM

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  Scorpions (prob. Lychas scutilus) under UV light. This photo shows how UV reflectivity on different parts of the body varies. In fact, those variations have been proposed as a way to examine scorpion morphology without using electron microscopy. Photo © Nicky Bay.

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  Scorpion mother with her young riding on her back. Illuminated with Ultraviolet torch and a red LED. Note that the kids do not glow under UV light! This reflects changes in their exoskeletons as they mature. In this photo the young are a bit older, and you can start to see the reflective pattern develop on their exoskeletons. Photo © Nicky Bay

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  Harvestman (Opiliones) under UV light. In the US, these are also sometimes called Daddy Long Legs. They are not spiders, and do not build webs. They are often scavengers, and will eat pretty much anything. You can see a photo of the same animal in normal light here; it's...well. In a discussion of how to describe the color we came up with "booger"; "snot"; and "Jolly Rancher Green Apple." You should probably never accept candy from that last person. Photo © Nicky Bay.

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  Millipede under UV light (Diplopoda). Millipedes under UV look like a strange tiny train from Studio Ghibli. Photo © Nicky Bay

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  This spider (Paraplectana sp) is a nice example of how fluorescent compounds are not evenly distributed within cuticle. What that means for the spider--or if the glowing is important to spider behavior--is not known. In regular light, this is a pale yellow and white spider. Also, I propose the the common name of the 1-Up spider. Image © Nicky Bay

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  This lovely spider looks quite different during the day--it's known as the Bird Dung Spider (Pasilobus sp.). Yes. It looks like bird poo in normal light. Recent research suggests many spiders may fluoresce, and that some also have fluorescing compounds in their blood. Overall, 41 genera and 19 families of spiders are known to glow under UV light. Photo © Nicky Bay

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  This Crab Spider (Tmarus sp.) has an interesting pattern--its legs and cephalothorax reflect UV, but not its abdomen. Photo © Nicky Bay

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  Scorpion (prob. Liocheles australasiae) Illuminated with a 365nm ultraviolet LED (6s) and ambient light. Photo by Nicky Bay.

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  Another shot of the Harvestman (Opiliones) under UV light. This wasn't one of Nicky Bay's favorite photos, but I love it and asked to include it. It shows what we might see if we were a tiny animal, watching this larger one moving by in the night. Wonderful and unexpected colors and patterns. Photo © Nicky Bay

You might not realize that all around you, an amazing show is going on. Many arthropods (insects, spiders, and relatives) have a secret: They glow under ultraviolet light.

Lightning bugs and other bioluminescent animals produce their glow from a chemical reaction. Scorpions and some relatives produce a blue-green glow via fluorescence. Under ultraviolet light (320-400 nm), molecules in their exoskeleton absorb and re-emit UV as visible light (excited electrons are involved, but let’s skip the details for now).

Photographer Nicky Bay has documented the way in which a wide variety of arthropods glow under UV light. Honestly, I can’t get a decent picture with a regularly lit camera, so I’m in awe of his photos, which he graciously allowed me to reproduce here. I asked Nicky why he started shining UV light on animals he was photographing, and I loved his answer:

Macro photography to me, has been about discovery of nature and opening a special window into a realm surrounding us that is often overlooked. UV expands this spectrum and in a way, exposes unique visuals and beauty normally not visible to the naked eye. Casting UV light on everything we see can sometimes lead to pleasant surprises, and I enjoy opening this “window” to everyone.

 

I could not ask for a better statement about Charismatic Minifauna.

Why do these arthropods glow, anyway?

Arthropod cuticle is non living, and made up of many crosslinked layers. Diagram courtesy BIODIDAC.

Short answer: we don’t really know for a lot of these animals. For non-scorpions, a lot of the literature is pretty much summarized as “Whoa, Dude! It Glows!”

For scorpions, the mechanism of the glow has been studied in more detail. Scorpions have “cuticular fluorescence.” Basically, compounds in their exoskeleton absorb and re-emit ultraviolet light as visible light (light humans can see). The exoskeleton of an arthropod is made from composite materials that are both strong and flexible. It’s the outermost layer, epicuticle, that produces the glow, and it seems to be something that changes chemically as the animals grow.

Two compounds are involved in scorpion UV fluorescence: beta-carboline and 4-methyl, 7-hydroxycoumarin. You might recognize coumarin as a common plant compound, and it’s often used as a perfume or in cinnamon flavors. I do not advise sniffing or licking a scorpion to see if they taste like a Cinnabon, though.

Some interesting ideas have been proposed for why scorpions and other arthropods glow like this. While humans can’t see UV light, most insects can, and much of the world around us looks quite different in UV light. Some experiments show that scorpions may use presence of UV light as a way to detect shelter. (They determined this by putting tiny little goggles on the scorpions that blocked their vision; sadly, no photos of that were in the research paper.) Others have proposed this glow is a leftover from the Early Devonian period when land was first occupied by giant scorpions and millipedes. UV-reflecting compounds might have helped those early ancestors tolerate time in the sun. We do know that coumarins in plants have a sunblock function for young seedlings.

If you’d like to see more amazing UV photos from Nicky Bay, check out his Flickr set of more tiny glowing animals.

Source.

[tarenna]

Another cracker from Tripsis. Respect.

[BreakingBarrett]

Amazing photos!