# Why Scorpions Glow In Black Light.



## pimpin_posey (Feb 21, 2006)

So I may be the last one to know but i figured out why scorpions glow under black lights. They glow because their skin excretes a chemical that keeps moister in their bodies. The scopions themselves dont neccisarily glow its the chemical covering their whole body.


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## Hoosier (Feb 22, 2006)

how did you find out about this?


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## Tony (Feb 22, 2006)

I'll go first-they dont have skin...


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## ScorpDemon (Feb 22, 2006)

be sure to pass that info on to all the herpetologists out there. They still don't know why scorpions glow under UV light. Just give them a heads up, it will save them a lot of time, money and further research and study.


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## pimpin_posey (Feb 22, 2006)

*Hey*

I could be wrong it just seems like a really logical way to think of it. and fine their "exoskeleton" ;P better


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## kahoy (Feb 22, 2006)

*might try this*

try using Black light in a...

newly dead scorp

on 1 day dead scorp

on 2 day dead scorp

3 day

4 day

5 day

1 month (if still whole)

any removed part of a dead scorp

on a sheded exoskeleton

on molting scorp (i mean while a scorp is molting)

sundried scorp

dead/alive scorp body underwater

cut an alive scorp in half and UV it.




this is for experimenting only not for doing such thing.

i would try this if i have any UV.


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## skinheaddave (Feb 22, 2006)

A fair bit is known about how scorpions flouresce and it is actually molecules within the exoskeleton, not secreted.  That being said, there may be a connection with the chemicals and water retention, as mentioned by Cloudsley-Thompson in a brief snippet in a journal article (I'm at work now and can't look it up, but I have the paper at home).  I am curious how you came to this conclusion.

Cheers,
Dave


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## ScorpDude (Feb 22, 2006)

Could their ability to glow be linked with their resistance to radiation? maybe the exoskeleton reflects it as visable light, so none of it is absorbed.


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## reverendsterlin (Feb 22, 2006)

if it is due to molecules in the exoskeleton then why will the spermatafors flouresce as well, due to the liquid in the packet?


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## fusion121 (Feb 22, 2006)

The best theory seems to be that scorpions glow as a result of the natural make up of their cuticle. As their exoskeleton hardens (after a moult) a process of oxidative cross linking occurs. This process produces the chemical that makes scorpion glow; a pretty simple molecule that sits in the cuticle of the scorpion, when it interacts with UV light it emits that characteristic blue/green light that we are all familiar with. The interesting question is whether the fluorescence is simply a serendipitous by-product of the chemistry of the scorpion cuticle, or whether it actually serves a purpose.


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## fusion121 (Feb 22, 2006)

reverendsterlin said:
			
		

> why will the spermatafors flouresce as well?


They don't


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## lucanidae (Feb 22, 2006)

> be sure to pass that info on to all the herpetologists out there. They still don't know why scorpions glow under UV light.


I don't think they ever will.....herpetologists study reptiles and amphibians, I'd say it's the arachnologists who would be interested.

I've always been told the chemical is some ion of phosphorus that is produced by the scorpion and not uptaken.  Many researchers will tell you it's a passive by-product of some other chemical pathway and actually has no purpose.  Scorpions can't see it, and there is not much if any UV radiation at night for anything else to see it.  It seems to serve no biological purpose whatsoever.  

Water retention is accomplished by the wax layer of the epicuticle which is located directly underneath of the cement layer.


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## Ecilious (Feb 22, 2006)

I blame God.


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## skinheaddave (Feb 22, 2006)

fusion121 said:
			
		

> The interesting question is whether the fluorescence is simply a serendipitous by-product of the chemistry of the scorpion cuticle, or whether it actually serves a purpose.


The interesting question indeed.  



			
				lucanidae said:
			
		

> Scorpions can't see it,


Actually, they can see within the range of the emmitted light.  In fact, the peak for sensitivity for the extraoccular light sense of Urodacus sp. as presented by Zwicky (1970) falls right in the green-blue portion of the spectrum.  As for the other biological purpose, there are several theories I've heard proposed or thought of myself -- but none have been tested to the point where they can be supported as causes from an adaptive standpoint.   For the bit about its link to water retention, refer to:  CONSTANTINOU C. & CLOUDSLEY-THOMPSON J.L. (1985) Transpiration in ultra-violet light from the scorpion. News. Brit. Arachnol. Soc., 44: 7.  To summarize, the water loss from a single specimen of A.crassicauda was evaluated over three days.  It was then placed under UV light and evaluated again over fifteen days.  The results were practically significant, though with only one specimen they were obviously not statistically significant.  Regardless, it does raise some interesting questions.  As far as I know, there was no published follow-up to this little experiment.

Cheers,
Dave


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## TRowe (Feb 22, 2006)

Whether this is relevant or not I do not know, but, I've noticed that the edges of silicon wafers fluoresce almost identically to scorpions when exposed to ultraviolet light.  I wonder if the fluorescent chemical is shared between most circuit boards and scorpions?  If that's the case, then it may make it very easy to isolate that chemical in scorpions.  

Just some food for thought, 

Tim


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## skinheaddave (Feb 22, 2006)

http://chem.ps.uci.edu/~dlvanvra/peptides.html

Cheers,
Dave


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## redhourglass (Feb 22, 2006)

Hi all,

This topic is and always will be a great debate.  I concur with Oliver's statement below which in my opinion is more intriquing from an evolutionary standpoint or not...



			
				fusion121 said:
			
		

> The interesting question is whether the fluorescence is simply a serendipitous by-product of the chemistry of the scorpion cuticle, or whether it actually serves a purpose.


Great link Dave !

Sinc. Chad


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## kahoy (Feb 23, 2006)

great link Dave, thanks for added info.


for me,
 better to ask an scorp!!!


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## lucanidae (Feb 23, 2006)

I accessed the study you sent me the citation for.  I don't understand this expieriment, they simply put a scorpion under UV light and it lost more water..... kindof.  In order to make this a good study they would need more scorpions as you mentioned and also need to strip the scorpion of the UV reflecting chemicals and test against a scorpion that did have them.  Or they could do a paired test, test an individual, then strip the chemicals and test the same individual.  With at least 30 individuals they can call it significant. 

The thing of it is, there is zero or almost zero UV light emitted in the desert at night. So even if the scorpions could see the reflections it wouldn't mean anything because their is no UV light to reflect.  Also, water loss dosen't seem to be the issue in terms of light, scopions are noctural and spend the daylight hours out of the sun; once again, we are lacking UV light to reflect.  We should remember that scorpions were orginally acquatic (and HUGE) and perhaps (as suggested by some) the phosphourescent chemicals are a leftover byproduct of from something important to aquatic life.  We do see a most bioilluminescence in ocean fauna.


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## kahoy (Feb 23, 2006)

*yep thats right!!!*

ive seen also those corals that glow under the sea, but when raised to the surface, they become greyish and dull. i did find also some of that statement is some biology books.:? 

probobly in their past life, they use this luminance to interact to each other,:?  or...










...i dont know! :wall: 



better ask kingkong. he got a lot of those giant in his island . or better go to skull island if you didnt understand kingkong.  

i love those gaint crickets, but still hoping not to have me as their FOOD!!!


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## skinheaddave (Feb 23, 2006)

First off, I don't know how practical stripping the chemicals is, as they are an intrinsic part of the exoskeleton.  You can remove the fluorescent properties through continuous exposure to UV light, but I don't imagine that this actually removes the molecules -- likely just damages them and removes their fluorescent capability.  The real key the experiment, beyond the use of more specimens (given a properly designed study and good statistical practices you might get away with less than 30, or might need more -- I'd like to know where you got this number without an experimental design) would be to set up your controls under a similarily powered light that emmitted in a different portion of the spectrum (but do you compensate for the power difference due to wavelength or not ... hmmm).  Alternately, you could expose some to UV light until they lost their fluorescence and then test them in conditions identical to the controls.  

Regardless of the practicality, let us assume that the study is done in full, with adequate statistical power, and a significant (statistical and practial) result is found.  The question then becomes whether the damage to the molecules results in a more porous cuticle, whether the UV has damaged something other than the fluorescing molecules, whether the trait is adaptively significant to primarily nocturnal animals etc. etc. etc.  My point was not that this study provides any answers -- merely that someone else had clearly been thinking about a connection between fluorescence and water retention but had only done a preliminary test and not a proper study.

As for the "no UV light" thing, this is not actually true.  Moonlight is actually just reflected sunlight and has a remarkably similar spectrum.  Furthermore, according to Kloock's study on avoidance by aerial scorpions (Euscorpius #21), there is at least enough UV light out at night to have a detrimental effect on the scorpions due to their fluorescence -- at least on or around a night with a full moon.  While scorpions do tend to prefer moonless nights, they DO come out on lit nights and will occasionally wander around during the day.

It is actually interesting that you mention the aquatic lifestyle, since there are some theories that revolve around that as well.  

Overall, a very interesting subject.

Cheers,
Dave


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## fusion121 (Feb 23, 2006)

lucanidae said:
			
		

> We should remember that scorpions were orginally acquatic (and HUGE) and perhaps (as suggested by some) the phosphourescent chemicals are a leftover byproduct of from something important to aquatic life.  We do see a most bioilluminescence in ocean fauna.


Fluorescence and bioluminescence are fundamentally very different properties, so I don't it as easy as that to draw comparisons to scorpion and other "light using" forms aquatic life. That said this link is very interesting:

http://oceanexplorer.noaa.gov/explorations/05deepscope/background/fluorescence/fluorescence.html



> In contrast, fluorescence in the organisms living on the deep sea bottom in the majority of cases seems to be a mere by-product of particular tissue biochemistry and is unlikely to play any particular adaptive role. Such fluorescence is usually weak, is not localized to particular body regions and has a wide featureless spectrum. The most common example of this is green fluorescence of the exoskeleton in crustaceans and other arthropods such as sea spiders


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## lucanidae (Feb 23, 2006)

The above quote is in perfect agreement with my argument, a by-product of a pathway in aquatic arthropods that produces flourescence for no reason.

Maybe scorpions avoid nights when the moon is out because of visible light....not because of UV light.  Besides, if flourescing actually helped retain water, then why do fossils of aquatic scorpions glow?  No reason for water retention in that case.  Why do rainforest scorpions glow?  Why hasn't flourescence evolved in other animals that need to retain water in the desert?  The point is, there are to many blattant inconsistensies with the water retention hypothesis.

Oh, and 30 is a statistical rule for a good paired test expieriment.


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## Scorpfanatic (Feb 23, 2006)

im all blown away by this thread.. hmm.. ill keep reading...


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## fusion121 (Feb 23, 2006)

lucanidae said:
			
		

> The above quote is in perfect agreement with my argument, a by-product of a pathway in aquatic arthropods that produces flourescence for no reason.


Yes I'm also in the camp that’s merely a quirk of chemical fate, which may have served a purpose earlier in scorpion evolution. I was merely pointing out that you keep changing terms, fluorescence, phosphorescence ( a sub-set of fluorescence) and bioluminescence all mean different things. The only one relevant to scorpions is fluorescence.


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## skinheaddave (Feb 23, 2006)

> Maybe scorpions avoid nights when the moon is out because of visible light


Entirely possible.  That being said, the Kloock study exhibits that there is a cost associated with the fluorescence (purely a function of the UV light) so a scorpion that bypassed whatever pressures are associated with the visible light would still have a cost associated with the UV light.  In other words, UV does have an effect -- doesn't mean it is adaptive, but it does mean you can't use a "no UV at night" argument to dismiss that it may be adaptive.  



			
				lucanidae said:
			
		

> The point is, there are to many blattant inconsistensies with the water retention hypothesis.


Absolutely nothing you have mentioned removes the possibility that the molecules responsible for fluorescence have a function in water retention.  It only speaks to adaptation -- not function.  I don't know the answers to your questions because, as has been mentioned several times already, there are very few studies of such things and it is hard to provide evidence for adaptive arguments.  Perhaps it would be wise to determine if and how fluorescence is linked to water retention (ultimatley probably a doable series of experiments) before we start proposing theories as to the why of it all.    

http://ethomas.web.wesleyan.edu/wescourses/2004s/ees227/01/spandrels.html is an interesting article (from some fairly well known scientists  ) discussing function, adaptation and where scientists go wrong thinking about them as completely linked.  It is entirely possible that scorpion fluorescence has no adaptive function and is simply a byproduct.  It is also possible that it was a byproduct to begin but has been selectively maintained in terrestrial scorpions.  It is entirely possible that it has a selective cost but has not been selected against because suitable mutations have never occured, there is a more pressing selective pressure in favour or, like the spandrels of San Marco, it is merely a necessary byproduct of another function.  It is entirely possible that it was a selective adaption in the first place but has been retained despite the loss of the selective pressure.  Point is, we don't know and it is very hard to establish evidence along these lines.  All of the adaptive/non-adaptive arguments, however, say nothing of function.  It is entirely possible that there is a real and testable reason for scorpions to lose  more water under UV light that is, itself, merely a byproduct.  It is also possible that the Constantinou & Cloudsley-Thompson test was merely a fluke.  You see what I'm getting at here?  There are plenty of possibilities and there is no point in drawing conclusions before testing them.      



> Oh, and 30 is a statistical rule for a good paired test expieriment.


Yeah.  It is in my first year stats textbook as a good rule of thumb for the division line between small samples and big samples too.  That being said, there are plenty of statistical methods that address issues surrounding smaller group sizes.  If we dismissed any group smaller than 30 as insignificant then we'd also have to dismiss an incredible amount of statistically sound studies that have been done to date.       

Cheers,
Dave


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## skinheaddave (Feb 23, 2006)

fusion121 said:
			
		

> Yes I'm also in the camp that’s merely a quirk of chemical fate, which may have served a purpose earlier in scorpion evolution.


And, as you know from our previous discussions, I am of the "you're probably right, but it might be fun to look into" camp. 

Cheers,
Dave


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## Alakdan (Feb 23, 2006)

I'm enjoying this discussion.

Pardon my ignorance guys. 

Are there other arachnids or insects that glow under UV light?  

Just a thought, one of the scorps set of eyes is probably sensitive to this luminescence, and this help them see and identify other scorps or prey.  Do you think there is a difference between the light wavelength reflected by each scorp specie?  Sort of a "signature" glow.


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## skinheaddave (Feb 23, 2006)

Alakdan,

I'm enjoying this too.  Since I graduated, I don't get quite as many opportunities for exchanging ideas with others -- especially those with an academic leaning -- something I always enjoy.

There are other arachnids and insects that fluoresce to some degree.  Some amblypygi fluoresce in certain parts.  Some spiders have high UV reflectivity, though they do not actually fluoresce.  There was one spider (Micrathena sp.) I ran into in Costa Rica that glowed as brightly as any white T-shirt under my UV light -- really not sure what was going on there or how common it is.  There's an early review paper (Lawrence, 1951, I think, but don't quote me on that) that reviewed the matter at the time.

There are a couple theories I've seen surrounding the fluorescence being used as a visual cue etc., but most of them seem poorly supported, especially in light of the scorpion's relatively poor ability to resolve images.  There is a theory that has been presented that they use their own fluorescence to aid in navigation -- but as far as I know this one hasn't been tested.  Regardless, median eyes and lateral eyes have both been shown to be receptive to the emmitted light and, as already mentioned, Zwicky found that the extraoccular light sense of Urodacus was sensitive to this range.

Cheers,
Dave


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## lucanidae (Feb 23, 2006)

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.


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## skinheaddave (Feb 23, 2006)

Do you have the citation?

Cheers,
Dave


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## lucanidae (Feb 24, 2006)

Chittka,Lars. Camouflage of predatory crab spiders on flowers and the colour perception of bees (Aranida: Thomisidae/Hymenoptera: Apidae) Entomologia-Generalis. 2001; 25(3): 181-187


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## skinheaddave (Feb 25, 2006)

Thanks.  I ordered it through interlibrary loan.  In the meantime, since this seems a hot topic, I've posted a short bibliography over here:

http://www.arachnoboards.com/ab/showpost.php?p=613493&postcount=34

Cheers,
Dave


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## cacoseraph (Feb 25, 2006)

lucanidae said:
			
		

> 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.


now that *is* interesting... flowers reflect UV to look like targets to bees... this is just spitballing... but i wonder if a part of the cause has to do with certain feeders being attracted to reflected UV making for better fed scorps.  course, this kind of clashes with the aquatic origins as i doubt there is much UV making it down into the briney deep =P

i expect as in much of life, there is no single cause, but combo of many different influences


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## TTstinger (Feb 25, 2006)

*my thoughts*

:wall: Ok many Ideas/theories and a whole bunch of big words. Good read though. But what if the reason scorp have a glowing talent is just this. Now think about this as if you were a bug such as a moth. Keep in mind to that we humans really have no way to know how any creature see's the world with it's eyes. 

Now a moth flies to light for unknown reasons and no test on earth could ever really tell us why, but they do. does it see that as light or maybe it see's it as dark just maybe the scorp has just developed it's self a lure. Making it's seem like the right place to go when really it will be the death of you.

Basically the scorp has evolved to become a bug attracting light source even with minimal UV not noticeable to the human eye, like the black lights we are so use to. In my mind this make the most sense, being loads of creepy crawlies are attracted to light source's. So in that theory the glowing talent become of some use to the scorp. I just do not think it has to do with keeping moisture. 

And futhermore for example purpose my sperm fluorescence under black uv light does that mean the little guy are trying to stay wet. I really think this topic is great for debate but in thee end I think That is all we will learn it make great debate. Oh and the military will make a great bomb that glows under UV or some rad weapon. they are making bullet proof vests out of spider web kinda cool I guess.

Sorry I could not use big words or drawn out terms and as far as test I can't pass a p test. But thats my thoughts on the whole thing, and I don't think UV has really any effects on scorps and If anyone has a scorp that does not glow because of too much UV I want to see it. Please post a pic of this non-glowing scorp please.

Thats my 2 cents and you can take them to the bank or whatever

P.S. you guys are the best


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## skinheaddave (Feb 25, 2006)

cacoseraph said:
			
		

> fed scorps.  course, this kind of clashes with the aquatic origins as i doubt there is much UV making it down into the briney deep


True.  But in the shallow seas where the aquatic scorps mostly seemed to live, there would be plenty of UV penetrating the first bit of water.  So, as with the "no UV at night" argument, it isn't overly compelling.



			
				cacoseraph said:
			
		

> i wonder if a part of the cause has to do with certain feeders being attracted to reflected UV





			
				TTstinger said:
			
		

> Basically the scorp has evolved to become a bug attracting light source even with minimal UV not noticeable to the human eye


For the theory that it is an attractant to insects, it may be worth your while to read this:

http://www.science.marshall.edu/fet/euscorpius/p2005_21.pdf

kind of throws a monkey wrench in that one.  Plus, remember that we are talking about fluorescence, in which the emmitted light is in the visible blue/green spectrum, not reflected UV.

Cheers,
Dave


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## TTstinger (Feb 25, 2006)

skinheaddave said:
			
		

> remember that we are talking about fluorescence, in which the emmitted light is in the visible blue/green spectrum, not reflected UV.
> 
> Cheers,
> Dave


 how do you know what is reflected to a bug. Somthing that see's in a way humans can never know, what we can't see maybe they can. There is a world that humans will never see nor will the know with science.
Sometime's the answer is the one staring you in the face but you don't see it cause your trying to hard to prove it with science and tests. 

your link did not work, send another.


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## cacoseraph (Feb 25, 2006)

skinheaddave said:
			
		

> True.  But in the shallow seas where the aquatic scorps mostly seemed to live, there would be plenty of UV penetrating the first bit of water.  So, as with the "no UV at night" argument, it isn't overly compelling.
> 
> 
> 
> ...


pretty experiment. does seem to indicate fluoresence has a negative effect on prey capture

i thought the fluoresence *was* reflecting the UV into visible via some crazy electron/photon intereaction, by definition


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## skinheaddave (Feb 25, 2006)

Reflection is when the light basically bounces off something.  So UV goes in, UV comes out.  Fluorescence is when the energy from the light going in (in this case UV) excites the molecules, which then become less excited, returning light of a different wavelength (in this case, somewhere in the  blue-green portion of the spectrum).  



> how do you know what is reflected to a bug


You stick an electrode in the nerves running from the photoreceptive cells and then expose it to various stimuli.  If there is an electric impulse then it senses it, if there is not then it doesn't.  That doesn't tell us how the creature percieves the stimuli -- just that it does or it doesn't.  We actually know quite a bit about insect senses, as they have relativley simple neurological systems which are much easier to study than more complex systems (mammals, for example).  Regardless, the point was that bugs being attracted to reflected UV would be different from bugs being attracted to fluoresced visible light -- you provided a potential explanation to an entirely different thing.

Oh, and the link has been fixed for a while now.  Try clicking on it again.

Cheers,
Dave


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## Metzgermeister (Feb 26, 2006)

*hmm*

I was looking though the scorp gallery, and theres a freshly moulted scorpion under a uv light, and it barely glows at all, while the shedded skin is glowing like crazy.  Perhaps it has something to do with the hardening of the exoskeleton??:? 

(p.s. a glowing scorp would look kinda intimidating to predators, whilst a newly molted one would neatly blend in with the darkness??)

http://www.arachnoboards.com/ab/gallery/showimage.php?i=883&c=502


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## skinheaddave (Feb 26, 2006)

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


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## lucanidae (Feb 26, 2006)

> 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. .


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## pimpin_posey (Feb 26, 2006)

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


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## yuanti (Feb 27, 2006)

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


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## Kugellager (Feb 27, 2006)

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
];')


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## Stylopidae (Feb 27, 2006)

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


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## Stylopidae (Feb 27, 2006)

Kugellager said:
			
		

> 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.*
> 
> ...


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


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## Kugellager (Feb 27, 2006)

Evil Cheshire said:
			
		

> I like the theory, but I have some questions.
> 
> Does the camoflauge serve a purpose today?


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

John
];')


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## skinheaddave (Feb 27, 2006)

Kugellager said:
			
		

> *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


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## fusion121 (Feb 28, 2006)

Kugellager said:
			
		

> 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.


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## skinheaddave (Feb 28, 2006)

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


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## fusion121 (Feb 28, 2006)

skinheaddave said:
			
		

> 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.


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## lucanidae (Feb 28, 2006)

> 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.


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## fusion121 (Feb 28, 2006)

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.


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## fusion121 (Feb 28, 2006)

fusion121 said:
			
		

> *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.


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## Kugellager (Mar 1, 2006)

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
];')


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## Kugellager (Mar 1, 2006)

fusion121 said:
			
		

> 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
];')


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## skinheaddave (Mar 5, 2006)

lucanidae said:
			
		

> 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


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## lucanidae (Mar 5, 2006)

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.


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## xgrafcorex (Mar 5, 2006)

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)"


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## lucanidae (Mar 5, 2006)

> 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)"


This dosen't tell us anything about why the scorpion flouresces, it just seems to be an overall description of the animal from a field guide.  
Most terrestrial arthropods have a waxy covering that prevents water loss.  This is seperate from the cuticle, which is what flouresces in scorpions.


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## kahoy (Mar 7, 2006)

actually complete data is not shown on the web.

base on my instincs(i dont know the spelling) you need money to get the truth, and you will not show that to others becoz they will just get it for free.

by then better have a lot of experiments.

just got a UV now, ill be going on an experiment soon.


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## ManicDan (May 10, 2008)

I hope no one minds me resurrecting this old thread, but I have been thinking about the UV florescence of scorpions a lot on my own, and brought the topic up in a thread and was directed to this one.  I had a theory of my own, that Kugellager previously stated.  

    The fluoresce of the scorpions being used as camouflage in the water has been running through my head lately.  After reading this thread I think that it is either the slight glow in the water to blend in, or the UV protection after they advanced onto land.

   Has anyone come up with any information since this thread passed away through the forum?  I think this is a great topic, and the thread is a great read, and it seems some conclusions were discussed, then it ended.  Any experiments done with this in the last year or two?


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## John Bokma (May 11, 2008)

Kugellager said:


> My sigificant concern regarding that fluorescence is an adaptation for water retention is, why haven't other arthropods not developed this feature?


some pillbugs do. I have somewhere homemade photos of it.

Very interesting read by the way and thanks for the bump


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