Why Scorpions Glow In Black Light.

[skinheaddave]

Yeah, that's one of my pics. And in terms of the how, it is definitely related to the hardening of the skeleton. "Cuticular sclerotization" would be the technical term, as used here: http://chem.ps.uci.edu/~dlvanvra/peptides.html

A lot more detail on this can be found in this article:
Stachel, S.J., S. Stockwell & D.L. Van Vranken. (1999) The fluorescence of scorpions and cataractogenesis. Chemistry & Biology 6:531-539.



Cheers,
Dave

 

[lucanidae]

Now a moth flies to light for unknown reasons and no test on earth could ever really tell us why, but they do.

We actually know a LOT more about insect vision than people on this forum tend to think. Check out the work of Dr. Cole Gilbert of Cornell if you want to know more.

We know why insects fly to light. Nocturnal flying insects use star and moonlight to navigate at night and bright lights throw off this navigation. The aren't attracted to the light at all. It would take one extremely bright scorpion to throw off the navigation of flying insects, and if you've ever seen a scorpion in the wild at night, they are not glowing. Plus, we know that scorpions are active hunters, no need for lures, and most of our U.S. species eat ground dwelling insects or each other. Intraguild Predation in scorpions is a huge topic. If they could see each other glowing, they most likely wouldn't get eaten by one another so much.

This is the article that started it all on intraguild predation in scorpions.

INTRAGUILD PREDATION AND COMPETITION AMONG DESERT SCORPIONS
POLIS-G-A and MCCORMICK-S-J
Ecology-(Washington-D-C). 1987; 68(2): 332-343
Abstract: Interactions among four species of desert scorpion were analyzed over a 9-yr period at two sites in the Coachella Valley, California [USA]. Although potential competitors that feed on similar arthropoid prey, these species also eat one another (i.e, engage in intraguild predation); heterospecific scorpions were found to form 8-21.9% of the diet. .

 

[pimpin_posey]

Well I'm glad i started a good discusion here and im glad to see so many experts on this.

 

[yuanti]

There was a small paper I found on a museum page:
http://www.museum.vic.gov.au/infosheets/10265.pdf

I dont know if this was already covered but just thought I'd add it in.

just states that: "due to the presence of a mixture of complex sugars and waxes that act as waterproofing compounds in the exoskeleton"

Just a very basic info sheet though

 

[Kugellager]

Here is my theory of why scorpions fluoresce. It is by no means a scientific study but one that I believe that should be studied. I neither have the resources or the inclination to study this theory further; although the right person might be able to persuade me to do so. Dave is also aware of this idea I came up with over a year ago.

Anyway, my theory is this: The blue-green fluorescence of the exoskeleton seen in nearly all members of the family Scorpionidae is a camouflage mechanism remnant from their former shallow-water near-shore aquatic origins.

Preliminary Points:
1) -The cuticles of nearly all species of scorpions fluoresces under UV light (Lawrence 1954 and Pavon & Vachon 1954)

2) -The metosoma of scorpions is sensitive to light i.e. Urodacus (480nm peak)/Heterometrus (568 & 440nm peaks) (Zwicky 1968 & 1970a)

3) -The fluorescent peak emission of all scorpions is 472nm (Koehler 1979)

4) -The best fluorescence is from UV light in the 320-400nm (3200-4000 Angstrom) range (Polis? not sure where I got this fact from, sorry)

5) -The UV absorption in sea water is lowest in the 350-500nm range ( http://oceanworld.tamu.edu/resources/ocng_textbook/chapter06/chapter06_10.htm & http://www.seafriends.org.nz/phgraph/water.htm#colour )

6) -The peak wavelengths of light leaving the water (reflected + re-emitted) is in the 430-500nm range. (http://www.soc.soton.ac.uk/JRD/SCHOOL/mt/mt001a_4.html )

So what does all this mean as I theorize it?

Fact: It is established that nearly all species of Scorpionidae, with the exceptions of a few troglodytic species, fluoresce near a peak emission of 472nm. Inferred: This fluorescence peak is right near the middle of the color of the light leaving seawater.

Fact: In addition, seawater is least absorptive of light in the upper UV range. Inferred: The upper UV range is where the cuticle of scorpions responds to UV light causing fluorescence.

My reasoning based on these established facts and inferences is that if the formerly aquatic scorpions were seen in the relatively shallow sunlit sea water of their origins, they would be nearly invisible due to fluorescence of their cuticle…At least to most creatures that would be attempting to eat them such as lizards, dinosaurs, early mammals or whatever was around during their aquatic existence. Today scorpions have evolved adapt to their terrestrial lifestyles and have developed various colorations depending on their environments. Theory: The fluorescence of Scorpionidae was evolved as camouflage and today is nothing more than a remnant of their former aquatic existence.

I have obviously not even attempted to put this idea up for any sort of review or publication other than here; but if anyone does wish to research/study this further please cite me in at least some minimal way.

John
];')

 

[Stylopidae]

I don't know if this has already been mentioned, but maybe it has something to do with attracting prey...

...some types of flowers glow under a UV light and quite a few reflect wavelengths of light that can't be seen with human eyes. Same with spiderwebs.

Edit: Just read page three. God, I look dumb

 

[Stylopidae]

Here is my theory of why scorpions fluoresce. It is by no means a scientific study but one that I believe that should be studied. I neither have the resources or the inclination to study this theory further; although the right person might be able to persuade me to do so. Dave is also aware of this idea I came up with over a year ago.

Anyway, my theory is this: The blue-green fluorescence of the exoskeleton seen in nearly all members of the family Scorpionidae is a camouflage mechanism remnant from their former shallow-water near-shore aquatic origins.

Preliminary Points:
1) -The cuticles of nearly all species of scorpions fluoresces under UV light (Lawrence 1954 and Pavon & Vachon 1954)

2) -The metosoma of scorpions is sensitive to light i.e. Urodacus (480nm peak)/Heterometrus (568 & 440nm peaks) (Zwicky 1968 & 1970a)

3) -The fluorescent peak emission of all scorpions is 472nm (Koehler 1979)

4) -The best fluorescence is from UV light in the 320-400nm (3200-4000 Angstrom) range (Polis? not sure where I got this fact from, sorry)

5) -The UV absorption in sea water is lowest in the 350-500nm range ( http://oceanworld.tamu.edu/resources/ocng_textbook/chapter06/chapter06_10.htm & http://www.seafriends.org.nz/phgraph/water.htm#colour )

6) -The peak wavelengths of light leaving the water (reflected + re-emitted) is in the 430-500nm range. (http://www.soc.soton.ac.uk/JRD/SCHOOL/mt/mt001a_4.html )

So what does all this mean as I theorize it?

Fact: It is established that nearly all species of Scorpionidae, with the exceptions of a few troglodytic species, fluoresce near a peak emission of 472nm. Inferred: This fluorescence peak is right near the middle of the color of the light leaving seawater.

Fact: In addition, seawater is least absorptive of light in the upper UV range. Inferred: The upper UV range is where the cuticle of scorpions responds to UV light causing fluorescence.

My reasoning based on these established facts and inferences is that if the formerly aquatic scorpions were seen in the relatively shallow sunlit sea water of their origins, they would be nearly invisible due to fluorescence of their cuticle…At least to most creatures that would be attempting to eat them such as lizards, dinosaurs, early mammals or whatever was around during their aquatic existence. Today scorpions have evolved adapt to their terrestrial lifestyles and have developed various colorations depending on their environments. Theory: The fluorescence of Scorpionidae was evolved as camouflage and today is nothing more than a remnant of their former aquatic existence.

I have obviously not even attempted to put this idea up for any sort of review or publication other than here; but if anyone does wish to research/study this further please cite me in at least some minimal way.

John
];')

I like the theory, but I have some questions.

Does the camoflauge serve a purpose today? I'd think it would make them fodder to parasitic wasps and such

 

[Kugellager]

I like the theory, but I have some questions.

Does the camoflauge serve a purpose today?

In my theory ...No it doesn't.

John
];')

 

[skinheaddave]

Fact: It is established that nearly all species of Scorpionidae, with the exceptions of a few troglodytic species, fluoresce

John,

As a preliminary step to looking into such matters, I tried to track down the source of the info on some species not glowing. So far, no luck. It seems to track back to a "vague idea that someone might have had" sort of thing.

Cheers,
Dave

 

[fusion121]

Here is my theory of why scorpions fluoresce.....

Hi
It’s an interesting theory but I don’t think it explains scorpion fluorescence. The main problem, I think, is that you are seeing adaptation where there is only coincidence. As I see it, it doesn’t work because:

This fluorescence peak is extremely broad (Scorpions fluoresce in range: 440-560nm, excitation occurs over a very broad range as well 275-600nm (Stachel et al., 1999)) and is exactly what you would expect from general delocalised organic systems, which occur in numerous places in nature. The molecules responsible (b-carbolines and coumarin) for fluorescence are not produced by any special cell/organ/gland etc. but is created by the process of cuticular sclerotization, a process vital to the scorpion’s survival. The fact that the fluorescence data seems to match up loosely with the properties of water is extremely weak evidence, the fluorescent properties of lots of things could be found to correlate with the same data.

During the day the intensity of fluorescence is relatively inconsequential when compared to the visible reflectance/emission spectrum (i.e. normal visible light coming off the scorpion), hence any camouflaging effect is going to non to very small (though it still could be a tiny selective pressure). Hence during the day fluorescence has virtually none/no bearing on the ability of a scorpion to be seen by predators, it’s simply too weak an effect.

We have no evidence that the aquatic/amphibious ancestors of scorpions fluoresced; fossil remains do not display fluorescence/ neither do the preserved cuticles of ancient scorpions (Fet et al. 2004). Indeed the adaptations theories of fluorescence tend to say that fluorescence may have evolved to protect the first terrestrial scorpions from the effects of UV light (Frost et al., 2001), after scorpions left the water.


Personally I think there are only 2 sensible explanations for scorpion fluorescence.

1.That it is an unintended consequence of the chemistry of the scorpion cuticle that serves no particular purpose. It seems of course that florescence can act as a deterrent to prey, but due to the way that scorpions regulate their activity I think this is a relatively minor negative factor and may well be compensated for by the advantages that the scorpions gain from their cuticular biochemistry.

2.That florescence in scorpions is a form of UV defence, all scorpions seem to fluoresce (as far as I can see there is zilch evidence that troglobitic scorpions don’t fluoresce). It interesting to note that scorpions seem to have evolved particularly strong defence against ionising radiation (perhaps again due the nature of their cuticle and its incorporation of metals), perhaps their early terrestrial ancestors had to cope with particularly harsh environmental conditions. It also interesting to note (purely from personal experience) that the intensity of fluorescence varies form species to species. Desert species universally seem to have relatively intense fluorescence, whereas some species inhabiting dark rainforest floors seem to display a much lesser level of fluorescence (e.g. T. paraensis). Could this be to do with the amount of UV protection they need? Of course this theory seems strange when one considers the habits of scorpions who generally avoid the sun, but then we know very little about the life histories of the first terrestial scorpions.

 

[skinheaddave]

In the ongoing saga of the x-linked threads, I detailed a little test confirming what is considered common knowledge here:
http://www.arachnoboards.com/ab/showpost.php?p=615639&postcount=35

We have no evidence that the aquatic/amphibious ancestors of scorpions fluoresced

I'm short of a source right now, but I'm pretty sure that at least some have been found that do. What is (Fet et al. 2004) or can you provide a quote?

any camouflaging effect is going to non to very small

I disagree that we should take this as the case without investigation. Matched with a suitable colouration, I envision fluorescence as having a potentially strong effect. Consider, if you will, P.imperator. It is a black scorpion which in sunlight will sometimes take on a greenish appearance. What do you think would stand out more at the bottom of a swimming pool? What about a shallow reef? I think this is one of the elements of the hypothesis that is most easily tested and ought to be before being dismissed.

Cheers,
Dave

 

[fusion121]

ht now, but I'm pretty sure that at least some have been found that do. What is (Fet et al. 2004) or can you provide a quote?

I can imagine that some specimens preserved in amber may well, but I looked through the literature I have and could find no reference to aquatic ancestors (look at Selden's works) displaying fluorescence. I'd be interested to hear if there are any examples of this that you can find reference to. The Fet quote is pretty general, he only toches on the subject:

The exceptional and excellent preservation of scorpion cuticle in Carboniferous assemblages is unique among arthropods, and has been described for a number of sites in Europe and North America (Bartram et al., 1987; Jeram, 2001). In some assemblages, only scorpion cuticles are present. Such preservation could be related to the unusual stability against biodegradation of the socalled hyaline cuticle—the upper layer of scorpion cuticle (Jeram, 2001), which has other unique properties such as fluorescence under UV light in all modern scorpions (i.e., fossil cuticles do not fluoresce).

I disagree that we should take this as the case without investigation. Matched with a suitable colouration, I envision fluorescence as having a potentially strong effect. Consider, if you will, P.imperator. It is a black scorpion which in sunlight will sometimes take on a greenish appearance. What do you think would stand out more at the bottom of a swimming pool? What about a shallow reef? I think this is one of the elements of the hypothesis that is most easily tested and ought to be before being dismissed.

I'm not denying that there is an effect; I simply think that it is negligible one and I'm pretty confident (well relatively )that any testing would bear out my assumption. I've seen the green sheen that P. imperator takes on (of course this is only obvious is particularly dark species) and it’s not a large effect (especially in most natural situations where UV intensity is often very low), and certainly when viewed from a distance effects such as contrast, colouration, shininess etc. etc. predominate when it comes to predatory identification.

 

[lucanidae]

I can imagine that some specimens preserved in amber may well, but I looked through the literature I have and could find no reference to aquatic ancestors (look at Selden's works) displaying fluorescence. I'd be interested to hear if there are any examples of this that you can find reference to

I was told by Dr. Linda Rayor that fossil scorpions that were aquatic still flouresce today. I'm looking into finding a written reference for this.

 

[fusion121]

I have read that scorpion cuticles found in coal deposits still fluoresce today but from what I gleaned they were from species that came after the migration to land.

 

[fusion121]

2.That florescence in scorpions is a form of UV defence...

Along that line it’s also interesting to note that the colonisation of the land by the "scorpions" began after the ordovician-silurian extinction events (about 450 million years ago). A postulate for at least one of these extinction events is the cosmological gamma ray burst, an effect of which would be to destroy a large percentage of earth’s protective ozone layer resulting is huge increase in dangerous UV light intensity. Could of course be completely irrelevant (and the date match ups aren't perfect), but it is interesting to consider.

 

[Kugellager]

My sigificant concern regarding that fluorescence is an adaptation for water retention is, why haven't other arthropods not developed this feature?...Actually that question applys for just about anything...why do no other arthropods fluoresce? Either way it is interesting.

John
];')

 

[Kugellager]

I have read that scorpion cuticles found in coal deposits still fluoresce today but from what I gleaned they were from species that came after the migration to land.

Yes but coal is usually created in a peaty/boggy/swampy habitat.

John
];')

 

[skinheaddave]

On the topic of arachnid UV reflectance; there is a really cool study on thomisid crab spiders of australia whose reflectence effects pollinator choice of flowers, really cool paper.

Okay, this is getting a bit off topic, but I finally had a chance to read this paper. I think you may have given me the wrong reference, as this paper deals with German spiders and does not actually test the choice of polinators. Plus, while it did have its merits, it was a little weak.

The author does a good job of justifying the study and explaining the methodology. To the end, he makes a good case for this sort of study. That being said, after presenting his results, the bulk of the discussion is attempting to backtrack and downplay the importance of the deviations from the sort of "perfect scenario" of a matched spectrum of reflectance across the board. Case in point -- he is sure to mention that to the eyes of a bee, the green component of the yellow spider matches well to the green component of the yellow flower. Since humans can detect light in the green portion of the spectrum, this is equivelent of me stating that my black car does not reflect light well in the red portion of the spectrum, and neither does my black hat I stuck on top of it. Still, point taken -- they blend in well. What he fails to mention is that the contrast in the greens between the spider and the center of the flower is actaully greater than the difference in the UV spectrum between the petals and the spider. The latter he deemed a significant deviation, the former he did not bring up.

Which brings us to the UV portion. Basically the only thing to note here is that the spider does not match the spike of reflectance in the UV portion of the yellow periphary. In other words, it has not adapted to match the flower in that portion of the spectrum (possibly for reasons that the author brings up himself).

In the end, what he has done is tested our intuitive grasp of the situation we have using our own senses (yellow spider blends in on yellow flowers, white spider blends in on white flowers), tested it beyond the bounds of our own vision and found out where the one surprise is (there may be some strong contrasts on the yellow flowers) and then come up with some (untested) theories on why this might be and why it might not matter so much.

I'm not saying this sort of science isn't important -- it is definitely critical that we escape the bounds of our own senses and this is the sort of study that lays the foundation for future studies and helps prevent errors due to oversight. The data is good, even if the discussion is not. If you have the reference to the paper that actually discusses predator preference and Australian Thomisidae, I'd love to get it.

Cheers,
Dave

 

[lucanidae]

Sorry about the bad reference for the crab spiders, my buddy did a research project on it and when I asked him for the reference he thought I was talking about a different paper. I believe this will be a little more helpful.


Heiling, A.M., Cheng, K. And Herberstein, M.E. (2004). Exploitation of
flower signals by crab spiders. Behav. Ecol. 15, 321-326.

Heiling, A.M. And Herberstein, M.E. (2004a). Floral quality signals lure
pollinators and their predators. Ann. Zool. Fennici 41, 421-428.

Heiling, A.M. And Herberstein, M.E. (2004b). Predator-prey co-evolution:
Australian native bees avoid their spider predators. Proc. R. Soc. Lond.
B 271, 196-198.

Heiling, A.M., Chittka, L., Cheng, K. And Herberstein, M.E. (2005).
Colouration in crab spider: substrate choice and prey attraction. J.
Exp. Biol. 208, 1785-1792.

 

[xgrafcorex]

found this while roaming around online..

http://animaldiversity.ummz.umich.edu/site/accounts/information/Centruroides_vittatus.html

"Other Comments

The striped scorpions body is covered with a waxy cuticle that helps prevent dessication. The scorpion cuticle flouresces under ultraviolet light, which helps when collecting or observing them at night. (Drees & Jackman 1998)"