Scorpion Fluorescence – August 2013

By Kevin Scott

Man’s highly developed color sense is a biological luxury- inestimably precious to him as an intellectual and spiritual being…. -Aldous Huxley inThe Doors of Perception

Aldous Huxley concisely described man’s fascination with things that shimmer and glow. The earliest admiration of the luminous was probably lightning at night, wildfires, the sun or a full moon.

To be sure, these things were revered and their causes unknown to the point that gods and goddesses were invoked, whose attributes described these phenomena.

Fast forward several millennia to the advent of artificial ultraviolet light and another curious phenomenon is observed: the fluorescence of scorpions under a black light. After the initial curiosity one comes to wonder what the purpose of this could be and how works.

Wild california scorpion while illumated with a blacklight

Light in the ultraviolet wavelengths is certainly not abundant at night (although the proportion of ultraviolet to white light is higher at night), so why the glow? The wavelengths in question abound during the day, but scorpions are decisively nocturnal animals that have well developed sensory mechanisms, allowing them to efficiently hunt and mate in low levels of light. The chart below describes some of these adaptations (Blass and Gaffin 2008).

Although all of these adaptations allow scorpions to capture prey, navigate and reproduce in low-light conditions, they do have several photosensory organs as well.

Emperor Scorpion, showing both fluorescing color and normal color

Scorpions have lateral and median eyes that are capable of detecting light magnitude changes and image formations, respectively (Gaffin, et al. 2011).   The median eyes are most sensitive to wavelengths around 500 nm (green) and secondarily sensitive to light in the 350-400 nm (ultraviolet) range (Machan 1968, Fleissner & Fleissner 2011).

In addition, scorpions have a metasomal element that is sensitive to light in the green area of the visible spectrum (Zwicky 1968, 1970; Rao & Rao 1973).

These technical details may at first seem superfluous until one thinks about the fact that when one views a scorpion under a black light, the black light and the green glow are in the same areas of the light spectrum as those to which the scorpion’s eyes are most sensitive; this is probably not a coincidence.

But this still does not explain the function of the fluorescence. Although the exact purpose is not known, there are a few hypotheses. There is the obvious possibility that no function is served at all.

Gary Polis suggested that fluorescence could act as a lure to draw prey in, but subsequent tests of this hypothesis show that insects will actually avoid scorpions that are fluorescing (Polis 1979; Kloock 2005).

One other theory suggests that fluorescence may play a role in courtship behavior, allowing one scorpion to tell whether a near by scorpion is of the same species and/or of the opposite sex (Kloock 2008). This would allow, from a distance, a scorpion to decide to approach (or be approached by) another that is either of the same sex or of a different species – either would be futile in a mating attempt. A negative photoresponse is observed in scorpions suggesting that the cuticle may serve as a photodetection device, however, it is not clear that fluorescence plays any role in this. One study showed that prolonged exposure to ultraviolet light caused a decrease in fluorescence (Kloock 2009).

Although the exact function has yet to be elucidated, mechanism by which fluorescence occurs in scorpions is relatively well understood. The scorpion’s exoskeleton is made from chitin, like other invertebrates. The compounds that fluoresce are found near the surface of the cuticle and relatively recently two molecules (4-methyl-7-hydroxycoumarin and beta carboline) have been isolated, both of which fluoresce in the presence of ultraviolet light (Stachel et al. 1999; Frost et al. 2001). Interestingly, Polis points out in his book The Biology of Scorpions that scorpions that have newly undergone ecdysis do not exhibit total fluorescence until 48 hours thereafter.

Fluorescence is observed in many life forms. Some of their functions are understood and some remain a mystery. Significant progress has been made with respect to that of scorpions, but more work is needed to fully understand the function thereof. For anyone who is interested in a deeper understanding of any of the topics discussed here, please explore some of the books and papers referenced below.

Blass, G. R. C & Gaffin, D. D. 2008. Light wavelength biases of scorpions. Animal Behaviour, 76, 365-73.

Gaffin, D. D., Bumm, L. A., Taylor, M. S., Popokina, N. V., & Mann, S. 2011. Scorpion fluorescence and reaction to light. Animal Behaviour, 83, 429-36.

Fleissner, G. & Fleissner, G. 2001. Night vision in desert scorpions. In: Scorpions 2001; In Memoriam Gary A Polis (Ed. by V. Fet & P. A. Selden), pp. 317-324. Burnham Beeches, Bucks: British Arachnological Society.

Frost, L. M., Butler, D. R., O’Dell, B. & Fet, V. 2001. A coumarin as a fluorescent compound in scorpion cuticle. In: Scorpions 2001; In Memoriam Gary A Polis (Ed. by V. Fet & P. A. Selden), pp. 363-368. Burnham Beeches, Bucks: British

Arachnological Society.

Kloock, C. T. 2005. Aerial insects avoid fluorescing scorpions. Euscorpius, 21, 1-7.

Kloock, C. T. 2009. Reducing scorpion fluorescence via prolonged exposure to ultraviolet light. Journal of Arachnology, 37, 368-370.

Machan, L. 1968. Spectral sensitivity of scorpion eyes and the possible role of shielding pigment effect. Journal of Experimental Biology, 49, 95-105.

Polis, G. A. 1979. Prey and feeding phenology of the desert sand scorpion Paruroctonus mesaensis (Scorpionida: Vaejovidae). Journal of Zoology, 188, 333-346.

Rao, G. & Rao, K. P. 1973. A metasomatic neuronal photoreceptor in the scorpion. Journal of Experimental Biology, 58, 189-196.

Stachel, S. J., Stockwell, S. A. & Van Vranken, D. L. 1999. The fluorescence of scorpions and cataractogenesis. Chemical Biology, 6, 531-539

Zwicky, K. T. 1968. A light response in the tail of Urodacus, a scorpion. Life Sciences, 7, 257-262.

Keeping Androctonus sp. in Captivity – July 2013

By Anthony Neubauer

Androctonus is the genus that contains the commonly called Fat Tail Scorpions. As the name suggests, these scorpions have an enlarged tail that allows them to possess more of their already toxic venom. They are recognized as some of the world’s most dangerous scorpions, and this should be kept in mind when choosing housing and while performing cage maintenance. The two most commonly available species in the U.S. hobby are the Yellow Fat Tail, Androctonus australis, and the Black Fat Tail, Androctonus bicolor. The care for each one is nearly identical as they are both naturally found throughout Africa and the Middle East.

Scorpions naturally have a slow metabolism, as they spend much of their time in burrows and under rocks. Because of this, they don’t require too large of an enclosure. However, they love to burrow and rearrange their cage, so one that allows burrowing is preferred. A cage size similar to a 5-10 gallon tank will be plenty large enough. The 12x12x12 glass reptile tanks offered by Exo Terra and Zoo Med make perfect and secure environments for these scorpions, as a lock can be purchased for added security. Since they are a desert dwelling species, a substrate that is dry and does not retain humidity is a must. I personally use a half-and-half mix of Zoo Med ReptiSand and Excavator clay. This allows your scorpions to dig and burrow as they would in the wild. Sand can also be used by itself, though you will want to offer more places to hide, such as flat rocks and wood. As for temperature, 75-80 degrees Fahrenheit is ideal. This can be achieved by placing a low wattage heat lamp on top, or a heat pad stuck to the side.  No special lighting is required as scorpions are nocturnal. They should be offered one or two appropriately sized crickets or roaches per week. A small water bowl can be offered, or the cage can be sprayed very lightly once or twice a month. They don’t require a lot of water because they get most of it from their food.

All in all, they are an easy-to-keep pet that doesn’t require daily care. If provided with a red nightlight, they can be seen throughout the night digging and rearranging their decor. However, they are a highly venomous animal that should be treated with respect. Their toxicity matched with their defensive personalities makes them a species that should only be kept by the more advanced and responsible hobbyist. Long tongs or hemostats should be purchased for performing maintenance, and under no circumstance should they be handled. If you’ve owned a lot of other scorpions and are ready to take it to the next level, then the Androctonus genus may be a good addition to your collection.

Dangerous Discussions: Part Two – November 2012

The Reptile Times

By Kevin Scott

In Part I of Dangerous Discussions I gave an overview of the definitions of and differences between poisons, toxins and venom. In Part II, I will go into greater detail in describing what toxins and venoms are and where they occur in nature. Of course, it would be impossible to talk about more than a handful of occurrences, so I decided to choose those that I find most interesting.


Toxins are organic molecules that are produced via biological pathways and are often used as defense mechanisms by animals. As mentioned in Part I, amphibians secrete substances that are toxic to bacteria and fungi, as the external part of their immune system. Some amphibians also secrete substances that are toxic to predators in order to prevent becoming prey. Tomato frogs and toads, for example, secrete thick milky substances that serve as irritants to potential predators. Arrow Frogs, as discussed in Part I, also secrete toxic compounds, these often being far more toxic than any produced by other amphibians.

The most potent of these toxins are steroid alkaloids, but nearly all of them are neurotoxic. Batrachotoxin is the most toxic of these, but other common compounds include epibatidine, histrionicotoxin and pumiliotoxin. If you are familiar with the arrow frogs, you can see the names of a few species in the names of these molecules. Batrachotoxin targets sodium ion channels, while epibatidine and histrionicotoxin target nicotinic acetylcholine receptors, and pumiliotoxin targets calcium ion channels.

Some, but not all, of these substances are actually produced by the frogs themselves. Many of the more toxic compounds, however, are actually produced downstream in the food chain. Pyrrolidines like epibatadine, and piperidines that are present in species found in the genera Oophaga and Ranitomeya, and Ameerega, Dendrobates and Ranitomeya (Lötters et al 2007), respectively, come from the ants that they eat.

Being that invertebrates and plants are the sources of these toxins, it is not surprising that it is not only the arrow frogs that possess them. Mantellas, the Arrow Frog’s Malagasy counterpart in terms of parallel evolution, also possess some of these toxins. One advantage of the fact that these frogs get this defense from their food items is that they are not nearly as toxic in captivity as they are in the wild.

Another frog that we commonly see in captivity, the Fire Walking Frog (Phrynomantis bifasciatus), also has toxins that can be used as a defense toward predators. This toxin’s identity is not known, but wild caught specimens can cause a burning sensation on the skin of a human, and it is strong enough to cause cardiovascular arrest in other frogs.

fire walking frog

The fire walking frog secretes a substance that can cause intense burning sensations in humans, and death in other amphibians.


There are many animals that produce venoms, including spiders, scorpions, marine invertebrates, fish, snakes, lizards and even mammals. Of these, a good handful can be found in the reptile industry.

Venoms are made up of mixtures of low-molecular-weight proteins, mucus, salts and organic compounds that include oligopeptides, nucleotides and amino acids (Colis 1990). This mixture can serve a variety of functions that include defense, prey submission and pre-digestion. Some of the types of venom are as they follow: neurotoxins cause neuromuscular paralysis that can result in immobilization and death; presynaptic neurotoxins block the release of the physiological transmitter acetylcholine, destroying the nerve terminal, and postsynaptic neurotoxins competitively inhibit binding of acetylcholine, preventing the transmission of nerve impulses across the synaptic gap; haemotoxins destroy red blood cells, and extreme cases can lead to renal failure; myotoxins damage muscles, especially respiratory muscles; cytotoxins destroy tissue, and these can aid in pre-digestion; nephrotoxins damage the kidneys (O’Shea 2005).

While the toxins that we have discussed in frogs are passively delivered, venom is delivered with an active delivery system. Special apocrine glands are connected to or in the vicinity of specialized hollow teeth or fangs, grooved teeth or a stinger (in the cases of the reptiles, tarantulas and scorpions that are common in the industry) that act as a penetration device that allows the venom to be administered.

vine snake

The fang of this vine snake can be seen within the red patch of gums behind the eye.

The most advanced delivery systems utilize fangs as an application mechanism. These fangs are specialized hollow teeth, through which the venom is delivered. These are used by vipers (including rattlesnakes) and elapids (including cobras, sea-snakes and kraits). Vipers have long, movable fangs that can be used to alternately progress, ‘walking’ a prey item down during feeding. When not in use, these fangs fold inward, allowing the mouth to close. Elapids are also front-fanged, but they generally have shorter, fixed fangs.

Only relatively few colubrids are venomous, but the ones that are have grooved teeth toward the back of the skull, which is known as being rear-fanged. These teeth are located below or behind the eye socket, and below a specialized salivary gland know as a Duvernoy’s gland, which secretes a toxic saliva that is used in subduing prey (O’Shea 2005).

While they may outwardly appear similar, the fangs of a tarantula or centipede are actually not teeth at all. Rather, they are chelicerae. Chelicerae are pointed appendages that are found in all members of the subphylum Chelicerata, that are used for grasping food or for defense. In spiders and venomous myriapods the chelicerae are hollow, and are used to inject venom from the connected venom gland.


The chelicerae of tarantulas, spiders and centipedes can be quite large, and are used for grabbing and envenomating prey items, as well as for defense purposes.

Scorpions have a pretty unique venom delivery system known as a telson, or stinger. At the end of the tail, a specialized anatomical development contains both the venom gland and the sharp point used for injection.


The telson of a scorpion contains the venom gland and delivery system in one specialized evolutionary development.


Although there are many other animals that are capable of delivering venom and the systems with which venom is delivered are far too complex to discuss in any depth here, I hope that the topics discussed here were enlightening. Furthermore, I hope that the content was deep enough to hold the majority of the readers’ attention, but straight forward enough so that no reader was excluded due to complicated writing.

O’Shea, Mark. 2005. Venomous Snakes of the World. Princeton: Princeton University Press.

Polis, Gary A. 1990. The Biology  Of Scorpions. Stanford: Stanford University Press.

Lötters, Stefan, Karl-Heinz Jungfer, Friedrich Wilhelm Henkel and Wolfgang Schmidt. 2007. Poison Frogs: Biology, Species and Captive Care. Frankfurt: Edition Chaimaira.

Bark Scorpions (Centruroides)

Bark Scorpions

By Dean Gramcko

Bark scorpions are a unique and fascinating group of scorpions indigenous to the Americas that are ideally suited to captive care in the vivarium. In America, the term Bark scorpion commonly denotes members of the genus Centruroides, a genus of Buthidae with between 70 and 80 species (different authorities disagree on certain species status). The genus Centuroides is an American taxon spanning the United States, Mexico, and Central America with established populations in South America and the West Indies, and smaller introduced populations in Africa.

The species of this genus are non-burrowing and hide among leaf litter, under stones or wood, among dead or living vegetation, or in the folds of plants or tree bark. Many species find their way into human habitations in their native areas. They are light bodied and agile,0 and able to climb vertical surfaces or cling upside down to rough surfaces as they walk.  A number of Centruroides species have very potent venom. Due to their defensive nature and frequent encounters with humans some Centruroides species are responsible for numerous deaths or dangerous envenomations in their native countries. C. exilicauda, C. sculpturatus, C. limpidus, C. noxius, and  C. suffusus all possess venom documented as having caused humans deaths, other species within the genus may possess medically significant venom. Many species within the genus possess venom capable of inflicting strong pain, but are not considered to have particularly toxic venom. Any species of Centruroides must be kept in an escape proof cage. A tight fitting lid is a must for any enclosure, as small gaps between lids and enclosures can provide perfect opportunities for escape. Some keepers apply a band of petrolium jelly around the upper lip of  the cage to help prevent young or small specimens from escaping.

Bark scorpions, like many Buthids, have a relatively short life cycle when compared to many other species. Specimens of C. guanensis may reach maturity in as little as 6 months, (most groups of scorpions take at least 1 to 2 years to mature, some species take much longer). They, as a group, are generally short lived with reported lifespans of between 1 year (C. insulanus) and over 4 years (C. gracilis). Most species within the genus Centuroides do not have established longevity records, but with maturation taking up to 3 or 4 years in C. vittatus, it is not unlikely that some specimens within the genus might live 6 years or more.

Bark scorpions are well suited to life in a vivarium. They are small in size (many measure less than 3” in length) and are one of few types of scorpions that can be housed communally with minimal chances of cannibalism. They are active hunters and as they do not burrow they are an ideal species to observe in the evenings. Most Centruroides species kept in captivity have proven to be prolific, and usually if males and females are housed together under proper conditions for long enough they will produce offspring. Bark scorpions are iteroparous and may give birth to between 1 and 4 clutches after a single mating, 2 probably being about average.

Bark Scorpion Tank

3 commonly available species are:

Centruroides sculpturatus: commonly called the Arizona Bark Scorpion, C. sculpturatus is generally considered to have the most potent venom of any U.S. scorpion, and while deaths are rare, it is the only U.S. scorpion that is well documented as having caused deaths not related to allergic reactions. It was formerly considered to be the same species as C. exilicauda, a Mexican species of bark scorpion now considered to be a separate species.

Centruroides vittatus: commonly called the Texas Bark Scorpion or Striped Bark Scorpion,  this is a distinctively marked species that is frequently available and common in the U.S.

Centruroides gracilis: This scorpion likely hails from Central America originally but has well established populations in Florida in the United States as well as Islands in the Caribbean. It is among the largest bark scorpions with adults measuring from between 4 and 6 inches.

Most species of bark scorpions kept in captivity do well under relatively similar conditions with varying temperature and humidity depending on species. Most specimens will thrive in a terrarium when given stacks of cork bark or stones to hide under. Care should be taken to ensure that cage furnishings will not shift and crush any scorpions. Live plants such as bromeliads or non-spiny succulents can improve the look of the enclosure (any plant used should be identified and researched to ensure it doesn’t present a threat to the scorpion), and provide hiding places for the scorpions. Water should be provided to any species at all times in a dish shallow enough to ensure scorpions do not become trapped and drown. Adding gravel to smooth bottomed dishes can help to guard against drowning. Most bark scorpion do well under similar temperature ranges (75 – 87 Fahrenheit). Most species do not require high humidity levels. Misting the enclosure lightly once weekly or bi-weekly depending on species is recommended.

Baby bark scorpions can be housed either in the larger enclosure with the adults, (though adult scorpions may sometimes cannibalize the young) or separated and raised up in small deli cups. The author prefers individual deli cups as it allows more precise control of temperature and humidity and eliminates any chance of predation from larger cagemates. Juvenile bark  scorpions development is measured most commonly with the term “instar” (referring to the stage of development present between two molts).

A newborn scorpion is termed “1st instar”. Upon completion of it’s 1st molt it is considered “2nd instar”.  The precise number of molts preceding adulthood varies between species and sometimes between genders of the same species. Generally bark scorpions seem to mature at around their 6th or 7th molt which for most Centruroides species occurs within 1 or 2 years (though some species may take much longer).

Their semi-arboreal nature, ability to live communally, and their readiness to reproduce in captivity make this group of scorpions fascinating to keep and an ideal candidate for observation in a vivarium. While the lifespan of individual scorpions are relatively short, these communal scorpions can be set up in large breeding colonies that will bring satisfaction to their keeper for years.


Francke, O.F.  & Jones, S.K., 1982. The Life History of Centruroides Gracilis (Scorpiones, Buthidae). The Journal of Arachnology, Vol. 10, pp. 223 – 239.

Polis, G. & Sissom, W.D., 1990. Life History. In G. Polis (Ed.), Biology of Scorpions (pp. 161 – 223). Stanford, CA: Stanford University Press.

Rein, J.O. & Teruel, R., 2012. The Scorpion Files. Retrieved from

Sissom, W. D., 1980. Life Histories of Two North American Scorpions: Centruroides vittatus (Say) (Buthidae) and Vaejovis bilineatus Pockock (Vaejovidae). Masters dissertation. Texas Tech University, Lubbock, TX.

Stahnke, H.L., 1971. Some Observations of the Genus Centruroides Marx (Buthidae, Scorpionida) and C. Sculpturatus Ewing. Entomological News, Vol. 82, pp. 281 – 307.

Stahnke, H.L. & Calos, M., 1977. A Key to the Species of the Genus Centruroides Marx (Scorpionida: Buthidae). Entomological News, Vol. 88,  pp. 111 -120.