Things That Glow Blue in the Night

by Dr. Dave McShaffrey

Even as a kid I was fascinated with flashlights and things that glowed in the dark. There was a toy called the Thingmaker with which you could mold plastic into shapes of animals - it used a lot of heat, way more than those sissy Easy-Bake ovens and their 40-watt light bulbs. The Thingmaker had an electric hotplate and you could really burn yourself with it. Lord only knows what chemicals were in the Plastigoop that you put in the molds, but when they came out with glow-in-the-dark Plastigoop, I was in heaven.

As an adult, my toy budget increased, and when I was investigating developing a forensic science program at Marietta (working from my start in forensic entomology; Dr. Neil Haskell and I were grad students at Purdue at the same time and I helped him on a few of his cases and wrote a couple of papers with him) I bought a UV flashlight. It was all the rage on CSI at the time (some say the character of Grissom on CSI was based in part on Neil). Anyway, for some reason I packed a UV light along on our first trip to Costa Rica in 2005, and there the fun began.


Scorpion - Blacklight (UV)



The first night at Santa Rosa we used the blacklight (which had LED's that emit a near UV light of about 400nm) to look for scorpions in the dorm rooms - and boy did we find them! Scorpions were first known to fluoresce under UV in the early 1950's - coincidentally the time a lot of prospectors were running around the southwestern US with blacklights looking for uranium (which also fluoresces under UV). In any event, this is basically what happens. UV radiation, which has a lot of energy, strikes molecules of beta-carboline in the integument of the scorpion. The structure of beta-carboline is such that it absorbs the UV and some of its electrons are excited to higher energy states. The electrons soon fall back to their normal states, emitting a bluish green light in the process (that's the blue you see in the scorpion above). For more on this see: .

beta carboline

Beta-carboline (Wikipedia)



We had a lot of fun with the scorpions in Costa Rica over the years, along the way learning that baby scorpions (which are carried on their mothers' backs) do not fluoresce; apparently they do not have the beta-carboline yet.

Scorpion with babies

Scorpion with babies; babies do not fluoresce.


We also found out that the ethanol in which we stored the scorpions would gradually become fluorescent itself, presumably as the beta-carboline leached out. Interestingly, just about any arthropod in our collection will leach a fluorescent material into the ethanol over time. Shine a UV light on our vials and they all glow a ghostly green.

We found scorpions in Utah as well at the Marietta College dinosaur fossil site. In Utah, we were able to capture enough scorpions to do a mark-recapture experiment and determine that there were hundreds of scorpions in our campsite. The geologists were a little concerned when, after catching and marking over 50 scorpions in the campsite we turned them all back loose...

Utah Scorpions

Scorpions from the Utah trip in 2008; below, Dr. Brown marking scorpions (carefully) for mark-recapture experiment. Note black UV flashlight.

marking scorpions


We continued to look at scorpions on our trips to Central America and found them in more places in Costa Rica, as well as in Guatemala and Belize. We also took a trip out west in 2010 and found a lot of scorpions there, particularly at the Valley of Fires campsite in New Mexico. Many of the students were intrigued by the experience, and there was a lot of nocturnal scorpion wrangling going on. In addition to the scorpions, we also found out that some lichens fluoresced.



Above: A scorpion from New Mexico and an image of a lichen. The lichen picture is a composite of an image taken with flash and one taken with UV light.

Perhaps the most interested student on the New Mexico trip was Derek Hennen. Derek was getting ready to start his junior year and already very interested in all things biological, but particularly insects and other arthropods. Later that summer he attended a millipede workshop given by Bill Shear and learned that some millipedes fluoresced under UV light. With his trusty UV flashlight in hand, he headed out to the Beiser Field Station with a few friends and the ground lit up.


Derek Hennen

Since then, we have spent a lot of time at the Beiser Field Station (and elsewhere) looking for things that glow blue (and red) in the night. In 2012, Dr. Katy Lustofin, Derek and I presented a poster at the Ohio Naturalists' Conference on the millipedes. Since then, Dr. Lustofin has taken the lead on the fluorescent millipede project. She is actively scouting the field station and the surrounding counties in Ohio looking for additional species that fluoresce, as well as trying to get a better feel for their distribution, habitat requirements, and daily and seasonal activities. Derek is in graduate school and Arkansas, looking for more millipedes and working on an updated key. I am also out looking for fluorescent millipedes, but also trying to find additional things that fluoresce under UV.




Here is what we have found as of Halloween, 2013:

Semionellus placidus visible light

This is where it started. Above, Semionellus placidus as it appears under normal light; below, the same millipede under near UV light (approximately 395nm if the manufacturer of the flashlight is to be trusted).

Semionellus placidus UV

And, below we have an animated GIF showing a transition as the lighting conditions are changed from visible to UV.

Semionellus placidus animation

Semionellus placidus

Above is Semionellus placidus at the field station on October 30th, 3013. Below are two additional images, one in visible and one in UV light, from the same trip.

Semionellus placidus

Finally, an image of Semionellus placidus with a mixture of visible and UV light:

Semionellus placidus

But Semionellus isn't the only species out there. We also have:


Euryurus leachii

Euryurus leachii (above in visible light, below in mixed visible/UV light).

Euryurus leachii mixed light

Euryurus leachii visible and UV

Euryurus leachii UV

Compared to Semionellus placidus, which we usually find on the forest floor, Euryurus leachii spends most of its time on downed logs or dead stumps. A third species of fluorescent millipede is Apheloria virginiensis, which is bigger than the other two and more brightly colored in the daylight. It also gives off a very strong almond or cherry smell when handled, a result of the production of benzaldehyde and HCN (cyanide). The benzaldehyde is very smelly and itself deters many predators; cyanide of course is toxic and these millipedes have enough to kill a small bird or a mouse (and enough to deter, but probably not kill a toad). For more on the millipede's chemical defenses, you might want to read Thomas Eisner's excellent book For the Love of Insects.

Apheloria virginiensis

Not all millipedes fluoresce blue. Derek found Pseudopolydesmus serratus there; it fluoresces red. You can see them in the photo below that Derek took:


Copyright 2012 by Derek Hennen

Millipedes aren't the only thing that fluoresce in the UV at the Beiser Field Station. How about this "daddy-longlegs" (harvestman):

Vonones sayi

Or this hornworm larva? It will grow up to be a large moth and is related to the caterpillars that feed on your tomatoes. This one was probably feeding on our Osage Orange trees.

Ceratomia hageni

Ceratomia hageni UV

In this case, we would never have seen it if it hadn't been for the fluorescence. This cat was on the forest floor in late October and we weren't looking for caterpillars at night.

The same could be said for this fly larva on the forest floor. It glowed bright green under UV, and that was the only reason I saw it. Many insects have a flexible protein, resilin, in their cuticles; resilin is particularly common at the joints and its fluorescence can be masked by thicker and darker areas of the cuticle. I'm not sure it's the resilin fluorescing here, but it was quite bright:

diptera larva

Not everything you might expect to fluoresce actually does. Glowworms are larvae (sometimes larviform females) of the fireflies that bioluminesce throughout the summer. Note that bioluminescence is different than UV fluorescence; bioluminescent organisms actually create light via chemical reactions, and thus can be seen in a completely dark place where there is no other light (I thought I saw a very bioluminescent organism out at the field station last week that turned out to be the green LED's flashing on one of our data loggers placed out there!). UV fluorescence requires a source of light such as a UV light. UV fluorescent organisms also fluoresce to some extent in sunlight, but the other colors reflected from their surfaces are usually brighter than the fluorescence and mask it. In any event, glowworms, like the adult fireflies, can actually produce light from special organs, and at the field station we routinely find them at night by their faint flashes of light. However, under UV light, they don't fluoresce:



Neither did this raccoon:

Racoon Procyon lotor


Back to the Osage Orange. We have noticed a number of plants fluorescing, but usually it appears to be fungi growing on the plant responsible for the fluorescence. I thought the bright green fruits of the Osage Orange might be candidates for UV fluorescence:

Maclura pomifera fruit visible light

But no:

Maclura pomifera fruit UV light

All you see in the image above is the blue glow emitted from the UV flashlight (I think they are purposely designed to give off some blue light so you can tell they are on). It's not that Osage Orange can't produce fluorescence, however - look at what happens when you shine a UV light on a cut stem:

Osage Orange wood UV

The cambium and phloem are full of some material that fluoresces. This is likely to be morin (AKA flavonol):


Flavonol (Wikipedia)


We've had to cut a few downed Osage Orange trees this year, and the wood chips glow a bright yellow - as do the roots of the trees pushed to the side when our road was put in in 2008.

Maclura pomifera wood under UV light



Like the lichens in New Mexico, some of our lichens at the Beiser Field Station also fluoresce:

lichen under UV light



This caterpillar is really strange. It belongs to a group called the slug caterpillars, and we had documented it at the Beiser a few years ago. We just found out that it is fluorescent under UV too:


Lithacodes fasciola under visible and UV

Note that the common name of that caterpillar is very misleading; although called a slug, it is not a mollusc but an insect, and will grow into a moth, believe it or not. Of course the Latin name fasciola reminds scientists of the liver fluke, which this caterpillar also resembles.



We're still looking for more things that glow blue in the night. Dr. Lustofin now has a growing list of millipede species - not all of which glow. One of those may be a species new to science, but we have to collect more specimens. It turns out you can only identify millipedes if they are males (you have to look at the gonopods, which are modified legs used by the male to transfer sperm to the female).

millipede gonopods


In addition, the gonopods of millipedes develop as they do - they may be mere nubbins even in a large, but not fully mature millipede:


So, it's going to take a while to catalog the millipedes. They're secretive, hiding in the leaf litter, under logs, in crevices and in the soil, and you can only identify mature males, which are only a part of the overall population. The fluorescent ones will be a bit easier to find, however. You can stand in one place at night with a UV flashlight and see a dozen or so.


We're also finding other fluorescent stuff - such as old flags we use to mark the trails, bits of shoelaces and paper, etc. As I mentioned earlier, we find a lot of fungi fluorescing, and both the small stream at our stream crossing and puddles elsewhere in the system often have a green fluorescence. The leaf pictured below is fluorescing weakly in the red spectrum, and it has some liquid on it that was fluorescing pure white.

leaf fluorescing under UV

Now, we all know from intro bio that chlorophyll fluoresces red after excitation with normal light; if you pass light through a chlorophyll solution and look at it at the correct angle you can see that. UV light is known to cause the same red fluorescence by chlorophyll, and UV also causes hydroxycinnamic acids and other materials including phenolic compounds in the leaf to fluoresce in the blue-green color spectrum (for more, see this article by Meyer et al.:, or the article by Morales et al. ).


Apparently this blue-green fluorescence (BGF) of leaves is a relatively new phenomenon, having only been reported in 1997, according to Morales et al. in the article linked above. Perhaps the BGF we are seeing in the waters at the field station are a result of these plant compounds leaching out as the leaves fall into the water. Also, it seems that certain plants have more of these compounds than others. There are a few potential capstone projects here!



And then there's this:


I didn't know what to make of this at first, but the more I look at it, I think it is a snail with a broken shell (Dr. Lustofin probably stepped on it!). It has a fair amount of UV-induced BGF, and this adds another phyla to the possible list of fluorescent organisms at the Beiser Field Station.