Zoologist, media consultant, and science writer, Dr Karl Shuker is also one of the best known cryptozoologists in the world. Author of such seminal works as Mystery Cats of the World (1989), The Lost Ark: New and Rediscovered Animals of the 20th Century (1993; greatly expanded in 2012 as The Encyclopaedia of New and Rediscovered Animals), In Search of Prehistoric Survivors (1995), The Unexplained (1996), Mysteries of Planet Earth (1999), The Beasts That Hide From Man (2003), and more recently Extraordinary Animals Revisited (2007), Dr Shuker's Casebook (2008), Karl Shuker's Alien Zoo: From the Pages of Fortean Times (2010), Cats of Magic, Mythology, and Mystery (2012), Mirabilis: A Carnival of Cryptozoology and Unnatural History (2013), Dragons in Zoology, Cryptozoology, and Culture (2013), A Manifestation of Monsters (2015), Here's Nessie! (2016), and what is already considered to be his magnum opus, Still In Search Of Prehistoric Survivors (2016), his many fans have been badgering him to join the blogosphere for years. The CFZ Blog Network is proud to have finally persuaded him to do so.

Dr Karl Shuker's Official Website - http://www.karlshuker.com/index.htm

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Thursday, 8 June 2017


The prince meeting his lindorm brother, from Folk Tales of the World, written by Roger Lancelyn Green, illustrated by Janet and Anne Grahame Johnstone, and published in 1966 by Purnell and Sons Ltd (© Roger Lancelyn Green/ Janet and Anne Grahame Johnstone/Purnell and Sons Ltd – reproduced here on a strictly non-commercial Fair Use basis only)

I owe much of my lifelong love of mythology to the wonderful works of Roger Lancelyn Green that my mother Mary Shuker bought for me when I was a child, in which he retold countless famous and little-known myths, legends, folktales, and fables from all around the world. Moreover, it was within these works that I first encountered many enthralling fabulous beasts and other folkloric entities, including the Japanese tanuki, the Mexican kuil kaax (click here for my ShukerNature coverage of this magical woodland spirit), the Australian kurreah (click here), and – in Green's delightful book Folk Tales of the World, exquisitely illustrated throughout in full colour by Janet and Anne Grahame Johnstone, which I still treasure to this day – the Swedish lindorm.

Lindorms are semi-dragons inasmuch as they occupy an intermediate echelon in the evolution of the dragon from the serpent. Typically (but not invariably) two-legged and wingless, lindorms have greater affinities with the serpents than with the classical dragons (in contrast, wyverns, which are also semi-dragons, possess not only a pair of legs but also a pair of wings, so they are closer to the classical dragons than to the serpents).

A sturdy typical two-limbed lindorm readily demonstrating its semi-dragon status, intermediate between a limbless serpent dragon and a quadrupedal classical dragon (public domain)

Incidentally, the term 'lindorm' should not be (but often is) confused with 'lindworm' – which technically should only be applied to wingless four-limbed classical dragons. In heraldry, however, it is commonly applied to lindorms.

Lindorms were commonly met with in churchyards, where they ghoulishly devoured human corpses, and would sometimes invade churches too. They occurred in great numbers amid the mountainous peaks of central Europe - indeed, the elaborate dragon-shaped fountain in Klagenfurt, Austria, was inspired by the discovery in 1335 of a supposed lindorm skull (it later proved to be from a woolly rhinoceros!).

A limbless Swedish lindorm, resembling a gigantic snake (© Richard Svensson)

Their favourite land, however, was Sweden, which contained quite a variety of versions, including legless lindorms and even one that sported a small pair of fore-wings instead of a pair of legs. But most Swedish lindorms were of the typical two-limbed variety. There are many traditional tales from this Scandinavian country concerning these particular semi-dragons, but perhaps the most celebrated example is the one that I shall now retell here.

A rare winged Swedish lindorm (© Richard Svensson)

Untold centuries ago, the Swedish monarch's queen lay in her bedchamber, about to give birth to twins - the fulfilment of many years of empty longing for the children that she seemed destined never to conceive. She smiled, as she remembered how, in final desperation, she had consulted a soothsayer who had assured her that in less than a year's time she would be granted two handsome sons - provided that she ate two fresh onions as soon as she returned home to the palace.

The advice seemed quite bizarre, but the queen was so aroused by the chance, however slim, that it offered to her that she made her way back to the palace at once, anxious to seek out the necessary vegetables without delay. Recalling this scene, she also remembered hearing the soothsayer calling after her, but as she had already told her about the onions, the soothsayer's message clearly couldn't have been of much importance, and so the queen hadn't wasted time turning back. Instead, she had continued her journey home, and upon arriving had ordered two crisp, mature onions to be brought to her immediately.

When she received them, the queen was so excited by the promise that these innocuous vegetables held that she ate the first one whole, without even stopping to peel the skins from it. Not surprisingly, however, it tasted quite revolting - and so in spite of her enthusiasm she spent time carefully peeling the second one, stripping away every layer of skin, before finally eating it. Nine months had passed since then, and now, precisely as prophesied by the soothsayer, she was about to bear her greatly-desired children.

'The Serpent of Arabia' – a lindorm sumptuously depicted in the Ripley Scroll, a 15th-Century alchemical manuscript of emblematic symbolism, and of unknown origin but named after Sir George Ripley, a famous English alchemist (public domain)

The palace courtiers and staff eagerly clamoured outside the royal bedchamber, awaiting the official announcement of the new princes' births. Suddenly, an ear-splitting scream echoed within the chamber - but it was not the lusty cry of a newborn baby. It was, instead, a shriek of horror - an eldritch wail that leapt unbidden from the throat of the royal midwife when she set eyes upon the queen's firstborn. It was male - but it was not human.

The queen had given birth to a lindorm - a hideous snake-like dragon, whose wingless elongate body thrashed upon the marble floor in innumerable scaly coils, and from whose shoulders sprang a pair of powerful limbs with taloned feet. Deathly pale and so repulsed by the creature that she was unable even to whisper, let alone scream, it was the queen, still in labour with her second child, who leaned down, took the young lindorm in her arms - and hurled it, with all the power that her loathing could summon, through a nearby window, from where the creature plummeted into the dense forest surrounding the palace.

Weakened from the exertion, she sank back upon the bed, and gave birth again - but this time to a perfectly healthy, fresh-faced boy, with golden hair and sparkling blue eyes.

Encountering a traditional two-limbed lindorm in Switzerland, from Itinera per Helvetiae Alpinas Regiones Facta Annis 1702-1711 by Swiss scholar Johann Jakob Scheuchzer, 1723 (public domain)

Years passed by, and the boy became a youthful prince in search of a bride - but what he found was his brother, the lindorm. The prince had been riding around the perimeter of the vast forest encompassing the palace when, without warning, a huge ophidian head had emerged from a thorny bush directly ahead. Rearing up until its green-scaled body resembled a towering tree, the lindorm gazed down at the youth with unblinking eyes of amber that effortlessly penetrated his innermost thoughts. And as the prince stared back, mesmerised and motionless before this monstrous entity, he heard its voice, intoning deep within his mind - a voice that assured him with cold, reptilian detachment and certainty that he would never find a wife until he, his elder brother, had obtained the true love of a willing bride.

Accordingly, over the next few months a succession of village maidens were given to the lindorm, in the hope of overcoming this barrier to the young prince's quest for a bride. Needless to say, however, none of the maidens were thrilled at the prospect of marriage to a lindorm, so none came willingly - and, inevitably therefore, none was accepted by the monster. The situation seemed irreconcilable - until one day, that is, when the next maiden selected to be the lindorm's bride had the good fortune to encounter beforehand the soothsayer whom the queen had consulted all those years ago. After listening sympathetically as the maiden spoke of her impending plight, the soothsayer whispered into her ear some words of advice that swiftly replaced her sadness with a smile of joy.

The maiden instructing the lindorm to shed its first skin, as portrayed by Arthur Rackham (public domain)

That night, the maiden was presented to the lindorm, who gruffly told her to take off her dresses - of which she seemed to be wearing a surprising number. She agreed to do this - but only after extracting from the lindorm the promise that for every dress she took off, it would shed a layer of skin. This it did, until only a single layer remained - and until the maiden was clothed in just a single robe.

The maiden removing her first dress, watched closely by the lindorm after shedding its first skin as demanded by her - illustrated by Henry Justice Ford (public domain)

Despite remembering the soothsayer's words, it was not without a degree of nervousness that she then removed this final gown and stood still, and naked, before the great dragon.

The lindorm moved towards her, and the maiden tensed - fearing yet desiring what was to come, for if the soothsayer had spoken truthfully to her there would be great happiness, and great love, ahead. And so she stood erect, motionless, as the serpentine monster leisurely, almost tenderly, enveloped her body in its scaly coils. She had expected them to feel cold and slimy, and was therefore pleasantly surprised by their warmth and softness - embracing and caressing her in their muscular folds.

Even so, she felt a flicker of terror rising within her - a desire to close her eyes, to scream, to flee, to do anything rather than remain here. Then the words of the wise old soothsayer came back to her, calming her mind, and she relaxed again.

Gazing about her, she noticed that the lindorm's last layer of skin was so thin as to be almost translucent, and was beginning to peel away, folding back upon itself like a cluster of withered leaves. At the same time, a strange green mist manifested all around, bathing the lindorm in a viridescent haze until she was aware of the creature's continuing presence only from the embrace of its sinuous body.

Gradually, however, the mist dispersed - and revealed that she was no longer wrapped within the serpentine coils of a lindorm after all, but within the firm arms of the most handsome man she had ever seen!

A somewhat Oriental-looking lindorm (public domain)

The soothsayer had indeed spoken truthfully - by following her instructions, the enchantment that had incarcerated him within the guise of a lindorm had been dispelled, and here was the elder prince, heir to the country's throne, and for whom the maiden would indeed be a very willing bride. The joyful marriage took place without delay, and after the old queen had given her blessing to the newly-weds, who were now the new king and queen, she felt someone lightly tap her shoulder.

It was the soothsayer, who revealed to her the information that she had not stayed to hear all those years ago - namely, make sure that she peeled both onions before eating them!

This ShukerNature blog article is excerpted from my book Dragons: A Natural History (1995). See also my more recent book, Dragons in Zoology, Cryptozoology, and Culture (2013), for detailed coverage of lindorms in mythology, cryptozoology, and natural history.

Tuesday, 6 June 2017


The ching shih (© Andy Paciorek)

In China, bloodsuckers are both plentiful and petrifying, but few are feared as greatly as the ching shih...

After another back-breaking day planting rice in the water-logged paddy fields near his village, the young peasant boy was looking forward to returning home, where he would stand before the fire until he felt warm and dry again. Cheered by these thoughts, he failed to notice at first that he was not alone as he walked away from the fields and on towards his village.

Just a little way behind him, a strange luminous orb, roughly the same size as his own head, was floating above the ground, but not in a passive, directionless manner. Had anyone been watching, they would have seen that this odd sphere was purposefully following the boy, drawing ever nearer, and glowing ever brighter, casting an eerie, unholy light upon his back.

Call it instinct, a sixth sense, or whatever you will, but suddenly the boy ‘felt’ that something evil was approaching. In panic he whirled around - and then he saw it!

Instinctively, he pulled back, gasping in terror as the mysterious sphere, now floating directly before him, rapidly expanded until it matched him in size. And as he gazed at it, almost mesmerised by its weird, uncanny light, the sphere took form and shape, metamorphosing into what the boy would have discounted as a horrific creature of nightmare – had he not been wide awake.

The sphere was now a grotesque humanoid figure, its tall thin body as shrivelled as an animate corpse, and covered in long green fur imbued with the lurid flickering pallor of decay and death. Thick strands of lifeless hair fell down upon its shoulders, and a wispy straggling beard hung from its chin. But all that the boy saw were its eyes – blazing like twin coals of hellfire.

He knew only too well the identity of this monstrous entity – like every child, he had been warned many times that such demons lay in wait beyond the safety of his village’s perimeter – but he had prayed that he would never encounter one. It was a ching shih – the deadliest form of Chinese vampire. And despite its emaciated appearance, it was also the strongest.

Sure of its power over the boy, the vile creature grinned malevolently, revealing an array of small but razor-sharp teeth that would soon pierce the boy’s body to drain it of blood, but first he needed to be killed. And so the ching shih opened its mouth wide, sucking in a deep intake of air. Moments later, it would blow it back out, directly into the boy’s face, to suffocate him with its toxic, foetid breath.

But in those few moments, a voice spoke to the boy deep inside his mind – the voice of his mother, urging him to flee back to the paddy fields, flee and never look behind him, not even for an instant, until he had reached them.

Immediately, the boy turned and raced away, so rapidly that the ching shih was startled, not expecting his sudden burst of activity. But then it began to chase after him, and as the boy ran on, he could hear the pounding of the ching shih’s feet close behind, and feel the heat of its foul breath upon the back of his neck.

The paddy fields lay just ahead, separated from him only by a stream, and as the boy’s pace slackened, exhausted from his headlong flight, he heard his mother’s voice again, telling him to leap over the stream into the fields. And then he remembered – like all Chinese vampires, the ching shih cannot cross running water. Summoning up his last atom of strength, the boy leapt, half-stumbling from weariness, but somehow he succeeded in clearing the stream, almost as if his mother had been there beside him, lifting him over its flowing water.

Standing partly submerged in the paddy fields, only then did the boy finally look back, and there stood the ching shih, on the stream’s far side, unable to cross, its eyes phosphorescent with malice. It opened its mouth, letting forth a deafening roar of impotent rage, then its form shivered and diminished, transforming once more into a glowing sphere that bobbed in the air before the stream but dared not float above it.

Suddenly, the sphere moved back, and sped swiftly away, soon vanishing into the distance. Only then, very cautiously, did the boy set off for home again, but keeping the stream beside him, not recrossing it until he saw his village’s friendly welcoming lights - very different indeed from the loathsome orb of evil that had so nearly claimed him as its latest victim.

This ShukerNature blog article is excerpted from Creatures of Shadow and Night, a book-in-progress written by me and illustrated by fantasy artist Andy Paciorek.

Saturday, 3 June 2017


Artistic representation of the Trinidad luminous lizard's possible appearance when glowing, as based upon Ivan T. Sanderson's claim (© Philippa Foster)

Among the fishes and several different taxonomic groups of invertebrate (including comb jellies, cnidarians, molluscs, insects, centipedes, millipedes, crustaceans, and annelid worms) are many bioluminescent species. That is, living creatures which actively carry out chemical processes to produce and emit light.

Officially, however, there are no bioluminescent species among the terrestrial vertebrates - but claims have been made that there may in fact be a notable exception of the reptilian kind.

I first learnt about, and then duly investigated, this fascinating yet surprisingly little-known case back in the mid-1990s, and here is what I uncovered at that time, followed by the extraordinary revelations that have occurred since then – yielding in this present ShukerNature blog article of mine the most comprehensive account ever published online.

A selection of fully-confirmed bioluminescent creatures depicted in a vintage illustration from 1890 (public domain)

In March 1937, during an animal collecting trip to the West Indies, American zoologist and cryptozoologist Ivan T. Sanderson visited Mount Aripo (aka El Cerro del Aripo), at 3,084 ft high the loftiest peak in Trinidad and part of this island's Northern Range. He had been capturing some freshwater crabs in a series of dark subterranean pools there when he suddenly spied a faint light in a crevice beneath a ledge. The light promptly went out, but Sanderson was curious to discover its source, so he flashed his torch into the crevice - and was most surprised to find a small lizard.

Attempting to coax it into his net, Sanderson gently tickled the lizard, but instead of running out it turned its head away - and as it did so, Sanderson was very startled to see both of its flanks momentarily lighting up "...like the portholes on a ship". When he finally succeeded in capturing it, this remarkable reptile lit up again, glowing brightly in his hand with a pale greenish hue that Sanderson subsequently likened to the glow produced by the hands and figures of a luminous watch.

As zoologists were previously unaware of any bioluminescent lizards, Sanderson was very thrilled by his discovery, which he documented in his book Caribbean Treasure (1939). Ironically, however, apart from its unique glowing ability the lizard, which was a male, seemed relatively nondescript in general appearance - with a long tail but short legs, a sharply-pointed muzzle, dark brown upperparts, and rosy salmon-pink underparts (turning yellow under its head) surfaced with large rectangular scales of plate-like form.

Ivan T. Sanderson's book Caribbean Treasure (© Viking Press, reproduced here on a strictly non-commercial Fair Use basis only)

Its only distinctive features were its body's lateral eyespots or 'portholes', constituting a series of large circular black blots running from the neck to the groin on both flanks, because each of these blots contained a vivid white bead-like spot. And it was these spots that were the source of the lizard's apparent luminescence, as determined by Sanderson during some basic experiments:

We made it [the lizard] hot and cold, and moist and dry alternately; we blew a loud whistle in its ear, we tickled it, and we subjected it to flashes of bright light...This creature seemed to produce its light in response to sudden emotional disturbance, rather than through actual physical reactions...The loud whistle, sudden winds, and flashes of light greatly agitated our lizard, causing it to switch on its 'portholes'. We noticed that this light was much brighter the first time it was switched on after the animal had been quiescent for a period, and more especially after it had previously been subjected to intense illumination.

Eventually, Sanderson shipped off his amazing little lizard to the British Museum (Natural History) in London, where it was studied in detail by fellow zoologist H.W. Parker. It was found to belong to a species already known to science (indeed, Parker himself had formally named and described it in 1935), but only just. An exceedingly rare member of the tejid (aka tegu) family Teiidae, and normally measuring 11-15 cm long, it was called Proctoporus (=Oreosaurus) shrevei (in honour of the very gifted American amateur herpetologist Benjamin Shreve), and had hitherto been represented in scientific collections only by a single preserved juvenile and one preserved adult female. Sanderson's specimen was therefore the first male of this species to have been brought to scientific attention, and until now no-one had suspected that it may be bioluminescent when alive.

Proctoporus shrevei (copyright holder presently unknown to me despite my having made considerable efforts to discover this; reproduced here on a strictly non-commercial Fair Use basis only)

During his visit to Trinidad, Sanderson collected seven more individuals of this species, and as preserved specimens these too were examined by Parker. In a paper published by the zoological journal of London's Linnaean Society in 1939, Parker revealed that it was sexually dimorphic, with only the males sporting the distinctive 'porthole' markings (a further reason why no bioluminescence had been reported from the specimens procured prior to Sanderson's), and that in every porthole the epidermis of the white bead at the centre was less than half the thickness of the epidermis of the black ring surrounding it. In addition, the white bead's epidermis was transparent, lacking any form of pigment. In other words, each porthole literally constituted a black-edged circular window.

How the portholes functioned, however, remained a mystery, because Parker found no associated nerve endings or an increased blood supply, thereby eliminating any likelihood that they were directly connected with the sensory or circulatory systems. Nor did he find any ducts connecting them with the exterior, or any complex lenses or reflecting structures.

Whatever they were, therefore, these portholes were clearly very simple in structure, and Parker offered three possible explanations for their luminosity. In life, the portholes may contain some substance that either glows when it breaks down (the principle of bioluminescence in various fishes), or glows when exposed to light (as with the paint used in luminous watches). The third option is that the transparent central beads of the portholes are underlain with reflective tissue. (A fourth possibility, that the portholes contain glowing bacteria which create their luminosity, can be rejected, because Parker did not report the presence of any bacteria within them.)

Ivan T. Sanderson as a young man (copyright owner presently unknown to me despite considerable searches made; reproduced here on a strictly non-commercial Fair Use basis only)

Inevitably, the prospect of a luminous lizard duly attracted attention from several other zoologists, who studied specimens of P. shrevei and various related tejids to find out whether any of them really did glow - but none of them did! And so in 1960, reporting at some length in the journal Breviora their own negative findings with P. achlyens from Venezuela and Neusticurus [now Potamites] ecpleopus ocellatus from Peru (both of which possess porthole markings resembling those of P. shrevei), American biologists Drs Willard Roth and Carl Gans rejected Sanderson's claims regarding P. shrevei's bioluminescence.

Yet Sanderson was an extremely experienced field zoologist, and Parker's histological studies convinced him that the portholes were genuine luminous organs. So who was correct? If P. shrevei were the only bioluminescent species, this would of course render worthless any comparative studies with related species. Moreover, at the time of my own initial examination of this case, only one zoologist other than Sanderson had actually investigated luminosity with living P. shrevei specimens, and he may simply not have stimulated them sufficiently for them to light up. (I subsequently found out that this latter zoologist was Prof. Julian S. Kelly – see later.)

My above account presents the situation concerning Trinidad's intriguing 'glowing lizard' that I had uncovered during my mid-1990s investigations. Since then, however, much additional information has come to light (pun intended!), and, as I discovered after unearthing it, this extra data includes some very significant new insights into P. shrevei and its alleged bioluminescent capabilities.

Map of Trinidad, highlighting its Northern Range, where Mt Aripo is (public domain)

First of all, it is nowadays deemed not to be a true tejid, so it is housed within a separate taxonomic family, Gymnophthalmidae, which contains many species. These are sometimes referred to as microtejids, because they are smaller than true tejids. Also, they tend to be quite skink-like in appearance, with certain species possessing reduced limbs.

I was pleased to learn that following further field studies, P. shrevei is no longer considered to be as rare as previously claimed. Indeed, the IUCN officially categorises it as being of Least Concern, and the IUCN Red List website states: "...although the distribution [of this species] is limited (with an extent of occurrence of 210 km2), the population trend appears to be stable, there are no current threats, and it occurs in at least two protected areas".

In addition, the IUCN assigns this species to the genus Riama, although quite a few other authoritative sources checked by me retain it within Proctoporus (so I shall do the same here for text consistency purposes), and refers to it via a very memorable common name that ties in with its supposed abilities – Shreve's lightbulb lizard. But is this name warranted?

Mark O'Shea lecturing at West Midlands Safari Park (© Ghaly-Wikipedia – CC BY-SA 3.0 licence)

During my original investigations of Shreve's lightbulb lizard in the mid-1990s, I communicated with the West Midlands Safari Park's internationally-renowned herpetological expert Mark O'Shea, famed not only for his numerous scholarly publications but also for his fascinating TV show O'Shea's Big Adventure in which he travelled the world seeking rare or unusual reptiles and amphibians. Mark was very interested in this mystifying lizard species, and I was delighted when he subsequently visited Trinidad to look for it. His search featured in 'Exotic Island', the tenth episode of his show's first series, screened in 1999.

After arriving in Trinidad, Mark and his camera crew teamed up with Caesar, a local guide, and with Dr Victor Quesnel (named as Quinnel in some reports), a retired Trinidad-based economic botanist who was also a very knowledgeable all-round naturalist (he died in 2014). But before they set off on their arduous trek in the hope of emulating Sanderson's original success in encountering this island's luminous enigma in 1937, they were able to chat with Javrien Capriata (aka Capriata Dickson), who had been Sanderson's guide back then, and was now over 80 years old (Sanderson himself had died in 1973). Happily, Mark's search proved successful too, as the team found two specimens, a male and a female. (Moreover, during a much later expedition in 2008, Dr Quesnel actually rediscovered the specific cave where Sanderson had captured his lizard in 1937 but which had not been found since then; it is now known as Sanderson's Cave.)

These two lizards were duly videoed in a dark room by Mark's cameraman while they were being illuminated artificially and for a time after the artificial illumination had been turned off. The video was then viewed closely to see whether there were any signs of luminescence from them. Not surprisingly, the female lizard did not glow, as it lacked the all-important porthole markings. Conversely, the male did indeed appear to glow for a short time after the illumination had been turned off. Unfortunately, however, it was not possible to determine whether this constituted bona fide glowing from the lizard, or whether it was merely a trick of the light caused by filming and the camera adjusting to the darkness after the illumination had been extinguished.

Ivan T. Sanderson in later years (© Dr Bernard Heuvelmans)

During the first half of the year 2000, I exchanged a series of letters with herpetological specialist Hans E.A. Boos from Port of Spain, Trinidad's capital, who is extremely knowledgeable concerning the reptilian fauna of this island. Needless to say, therefore, one of the subjects that we discussed was P. shrevei and its alleged bioluminescence. Hans was very sceptical about this, and even more so concerning the reliability of Sanderson's eyewitness testimony (it has to be said here that Sanderson was well known for exaggerating claims at times, although this behaviour may have been caused by a brain tumour that developed over time and apparently contributed to his relatively early death, aged just 62).

In one of his letters to me, dated 22 January 200, Hans revealed that he had kept specimens of this lizard species in captivity for a considerable time but had never seen them light up. He also noted that both Dr Quesnel and Trinidad-based zoologist/newspaper columnist Prof. Julian S. Kenny had attempted to repeat the conditions reported by Sanderson but again had failed to achieve any success in stimulating the lizards to illuminate. In a subsequent letter, dated 14 April 2000, Hans mentioned to me that during the previous evening he'd had dinner with Dr Quesnel and had discussed fully with him the subject of P. shrevei. Quesnel had announced that he planned to try to collect a couple more specimens and this time arrange for high-quality histological sections to be prepared, with the tissues of the portholes properly fixed, in the hope of deducing something new regarding their supposed luminosity.

On 3 October 2004, the Trinidad Express newspaper published a short article written by Prof. Kenny that expanded upon Hans's comment concerning his investigations of Shreve's perplexing little lightbulb lizard. After referring to Sanderson's capture and claims regarding this species, Kenny revealed that American zoologist Prof. E. Newton Harvey (died 1959), a leading authority on bioluminescence, had once asked him to conduct an experiment to confirm his belief that Sanderson's claims were unfounded. The Harvey/Kelly experiment involved injecting some living specimens of P. shrevei with 1:10000, and 1:1000 doses of adrenalin. This treatment had already been shown to trigger light production in bioluminescent fishes, but it did not induce any reaction in the lizards.

Prof. E. Newton Harvey (public domain)

Also in 2004, what is acknowledged to be the defining scientific paper dealing with this contentious species' reputed glowing behaviour was published in the Caribbean Journal of Science. One of its three authors was Dr Quesnel, who revealed that, in fulfilment of his hopes expressed to Hans Boos in 2000, he had indeed succeeded in conducting further field investigations of P. shrevei, in May 2001 and again in May 2002.

Two male specimens were captured in rock crevices near to a cave entrance at the summit of Mount Aripo – i.e. the same general locality as Sanderson's own discovery. After examining them in the field, Quesnel took them to a field station for further investigation, where they were studied under light and dark conditions at different times of the day. Yet no observations, either in the field or at the field station, revealed any light emission from the portholes. The same was true with a third specimen that had been captured and studied previously by Quesnel. Clearly, therefore, they did not appear capable of bona fide bioluminescence, i.e. the active generation of light by living organisms via chemical means.

But what about the prospect that the portholes were highly reflective, or perhaps even phosphorescent? (That is, reflecting incident invisible light as visible light but over a longer time period than in fluorescence and without heat.)

Vintage illustration from 1904 depicting a further selection of known bioluminescent creatures (public domain)

To test this possibility, Quesnel directed high-intensity light from a xenon lamp at the lizards from varying angles. No light was emitted by the lizards, thereby demonstrating that they were not phosphorescent. However, light was readily reflected by their porthole (ocellar) scales. As Quesnel et al. explained in their paper:

...if P. shrevei is observed along the same plane from which light is directed, the normally obvious white ocelli cannot be seen against the reflection from all other scales. But, when viewed from an angle oblique to the light source, the ocelli appear brighter, while surrounding scales show no reflection. By varying the angle of reflected light, an illusion is created that the ocellar scales are intermittently emitting light, thus providing an explanation of Sanderson's original account of the lizard "switch[ing] on its portholes." The illusion produced by the reflective scales also explains recent accounts, as well as Sanderson's description of the white ocelli "remain[ing] plainly discernable in a darkened box when the rest of the animal was invisible." The ocellar scales reflect and intensify ambient light while the darker ground coloration renders the rest of the lizard invisible in a dimly lit environment.

It was also noted that the illusory effect of the reflective porthole scales was enhanced by a varying in intensity of the black pigment surrounding these scales, and that this varying of the black pigment's intensity appeared in turn to be dependent upon the lizards' stress levels - because it became darker when the lizards were first handled, but faded somewhat after several minutes. The black pigment surrounding the porthole scales heightened their reflective effect, making them look a brighter white:

When viewed immediately after handling the lizards, the ocelli appear to pulse or fluctuate in brightness as the surrounding pigment changes intensity. After a quiescent period, the ocelli are still reflective but do not appear as bright as when the surrounding skin pigmentation is darker. Again, this could explain Sanderson's description that light from the lizard "was much brighter the first time it was switched on after the animal had been quiescent for a period of time," and "after one brilliant display... it refused to shine with full brightness." The darker dermal pigmentation, presumably associated with higher stress levels during handling, heightens the reflective appearance of the white ocellar scales. Decreased pigmentation during inactive periods gives the illusion that the lizard is not producing light at full intensity.

In short, these studies appear to have comprehensively refuted Sanderson's claims that Shreve's lightbulb lizard is bioluminescent. Instead:

...the lizard's unique scales act like small parabolic mirrors, reflecting light at oblique angles. The intensity of this reflectivity is, in turn, influenced by the intensity of surrounding dermal pigmentation and by the angle at which a lizard is oriented relative to a light source. Thus, ocellar reflection produces an illusion that light is emitted by P. shrevei at varying intensities, a phenomenon which obviously has confused a number of persons.

Partial view of the Northern Range, Trinidad, whose Mount Aripo is home to Shreve's still-mystifying microtejid (image cropped) (© Sanjiva Persad/Wikipedia – CC BY 2.0 licence)

Even so, one major light-related mystery concerning Shreve's very surprising microtejid still remains unsolved. Namely, why has so remarkable a morphological feature as this lizard's parabolic mirror scales evolved in the first place, and why only in male specimens?

These are questions that the study of Quesnel and his co-workers did not seek to answer, although, as they did point out, P. shrevei is a reclusive nocturnal species that inhabits dark localities and whose behaviour in the wild is unknown – all of which make any attempt at speculation fraught with difficulty. Nevertheless, it occurs to me that in view of their sex-specific and also age-specific occurrence, perhaps these scales' light-reflecting abilities function as a means of visual communication by which adult males attract adult females for mating purposes. An alternative option is that this light-reflection ability is used as a defence mechanism, to startle or ward off potential predators, but if this were true, why do only males possess the necessary scales?

Clearly it is high time that some comprehensive field studies were conducted in relation to this small yet very thought-provoking lizard, neglected by science for far too long, in the hope of finally shedding some much-needed light (in every sense!) upon the currently cryptic purpose(s) of its unique parabolic portholes.

The present ShukerNature blog article is a greatly expanded and fully-updated version of a short account that appears in my book Mysteries of Planet Earth (1999).