A review of the members of the genus Chaerilus in China with the description of one new species

 

Recently, Victoria Tang has published an extensive review of the species of Chaerilus Simon, 1877(Chaerilidae) from China. One new species is described.

Chaerilus herta Tang, 2025

The paper reviews the species found in China and discuss taxonomical challenges for the family and for scorpions in general. Also, the presence and level of UV fluorescence in this genus is discussed.  

Abstract:
The genus Chaerilus Simon, 1877 in China is preliminarily revised on a morphological basis, derived from the available literature and newly examined specimens. The robustness of several commonly applied species-level diagnostic criteria are evaluated. Ten species are provisionally recognized for China, including one new morphospecies, Chaerilus herta sp. n., described from 9 females, 40 males, and 2 juvenile females collected in Mêdog County. The current study only reveals and resolves several most elementary issues in the taxonomy of Chinese Chaerilus. Further molecular investigations are warranted until topotypes of certain species become available.

Reference:
Tang V. Current challenges and preliminary morphological reassessment of the genus Chaerilus Simon, 1877 in China (Scorpiones: Chaerilidae). Euscorpius. 2025(406):1-89. [Open Access]

Family Chaerilidae

A study of the fluorescent sensilla on the scorpion aculeus (stinger)

 

It is well-known that scorpions fluorescence under UV light. This also apply for the scorpion's stinger (aculeus), but previous studies has shown a lack of fluorescence in the distal aculeus. Graeme Lowe has recently published an article where he used SEM imaging to study UV fluorescence in the acuelus of many species.

He observed numerous brightly fluorescent punctae in the non-fluorescent distal aculeus. These punctae were identified as aculear sensilla coeloconica (ASC). The ASC probably have a chemoreceptive function.

The author suggests that the ASC are playing an important role in the sensory coordination of telson function when the scorpions are trying to sting their prey and inject venom.

Abstract:
The aculeus of the scorpion telson was studied by UV fluorescence microscopy. Numerous brightly fluorescent punctae were observed on the non-fluorescent distal aculeus, including the tip region. The punctae were identified as aculear sensilla coeloconica (ASC), and were connected to fluorescent canals running through the cuticle. ASC were present in both sexes, and in adults and immatures as early as the second instar juvenile, but were absent from the first instar. The distal aculeus was found to be encased in a thick, non-fluorescent dark exocuticle (DX), covering an underlying thin, fluorescent hyaline exocuticle (HX). Fluorescent ASC were recorded from 183 species belonging to 97 genera in 19 families, encompassing all major scorpion lineages. The number of ASC in the tip region, the width of ASC canals, and the depth of the tip region, all exhibited positive correlation and allometric scaling with respect to carapace length. Higher tip densities of ASC occurred in some buthids, and in Scorpionoidea. The ASC are probably ubiquitous across the Order Scorpiones, playing an essential role in the sensory coordination of telson function during prey envenomation.

Reference:
Lowe G. Star-studded stingers: fluorescent sensilla on the scorpion aculeus (Arachnida: Scorpiones). Euscorpius. 2024;2024(402):1-39. [Open Access]

Albinism in the buthid Olivierus martensii and review of albinism in scorpions in general

 

Albinism is known in many animals, but it is rare in scorpions. Victoria Tang and Zhenbang Liu has now published a very thorough article on this fascinating topic using albinism in Olivierus martensii (Karsch, 1879) (Buthidae) from China as an example.

The authors thoroughly describe and discuss all aspects of albinism in this species (origin of this phenotype, manifestation, and behavioral and ecological consequences of having this phenotype). Scorpion coloration in general is also discussed in relation to albinism.

Abstract:
This is a formal case report for the albinism in Olivierus martensii (Karsch, 1879). Albino phenotype is compared with its normal counterpart in terms of their morphology and behavior by cursory experiments. The examined 7 albino individuals (5 of which were adults) were smaller and more slender than their normal counterparts. However, these quantitative differences were not statistically significant and should be treated with caution due to the low sample size. Their abilities to detect both white light and UV light or UV-excited fluorescence were not significantly undermined, although their tendency to ensure a clear vision through self-cleaning behavior appeared to be reduced. Their heightened visibility on dark, leafmould substrate and greater crypticity on yellowish gravels may play a significant role in their natural survival. Additional evidence is required to substantiate this hypothesis as the function of scorpion coloration has been hardly studied. Several theoretical assumptions were proposed following a literature review on scorpion coloration and fluorescence, and this paper also serves as a brief synopsis of those aspects. Other three rare phenotypes in this species are also reported, defined here as piebaldism, hypomelanism and leucism. Given their existence, it is suggested that the loss of melanin in the epidermis beneath the ocelli is diagnostic for albinism in scorpions.

Reference:
Tang V, Liu Z. Albinism in Olivierus martensii (Karsch, 1879) (Scorpiones: Buthidae). Euscorpius. 2024(396):1-33. [Open Access]

Scorpion biology and folklore in Durango City, Mexico

 

Mexico is a hot spot for scorpion diversity and also hosts many of the worlds most venomous species in the genus Centruroides Marx, 1890 (Buthidae).  One of the most famous scorpion places in Mexico is "The City of Scorpions" Durango, where the infamous and very venomous species Centruroides suffusus Pocock, 1902 is very common.

 Eduardo Gonzalez-Ponce and several co-workers have recently published an interesting article about different aspects of the biology of the Durango scorpion including the scorpions' response to light, medical importance and the use of its venom for research and medicine. Of special interest is the description of how the peoples of Durango utilize the scorpions as souvenirs for tourists and as an exotic food source.

Abstract:
Scorpions are incredible venomous animals found on almost every continent. According to fossil data, these animals have been able to adapt to the different environments from the Cambrian period until today with minimal anatomical changes. Scorpions are mostly nocturnal animals, and their ability to detect and tolerate light stimuli seems to be an essential tool for their subsistence, homing and mating. Centruroides suffuses is the most predominant specie of scorpions in Durango City, Mexico. Interestingly, and despite their life-threatening venom, these predatory arthropod animals have been adopted by locals as part of the landscape and daily life, by including them as part of their folklore and their economic resources, and learning how to take advantage of their abundance. In addition, the venom of scorpions possesses potential for therapeutic uses, while the scorpions themselves represent a nutritional food resource rich in protein, which has been poorly explored so far. Therefore, they are an excellent model for exploring the interplay between light sensibilities, survival and therapeutic–medicinal uses. Here, we review some of the potential benefits of scorpions and share the ways people in Durango City, Mexico, use UV light devices to detect and avoid or catch them for business and research purposes.

Reference:
Gonzalez-Ponce E, Rodríguez-Rangel S, Martinez R, Alvarado A, Ruiz-Baca E, Miranda P, et al. Scorpions, Science and Folklore in Durango City. Diversity. 2023;15(6):743. [Open Access]

Characterization of aspects of fluorescence in the exoskeleton of scorpions

Scorpions glow (fluorescence) when exposed to ultraviolet (UV) radiation. At present, the biological functionality –if any– of this intriguing fluorescence is unknown and awaits further investigation.

Daniel López-Cabreraa and co-workers recently published an article investigating some aspects of fluorescence in the exoskeleton of 24 species of scorpions. The study suggests that the intensity of fluorescence is heterogeneous throughout the scorpion's exoskeleton (some parts fluoresce more intensely than other). Also, they conclude that fluorescence may correlate directly to the ecomorphotype of the scorpions.

Abstract:
Scorpions are a mesodiverse and nocturnal group of arachnids inhabiting most biomes worldwide. Different species of scorpions have divergent adaptations to the substrate they live in, but most of them share an intriguing characteristic: their exoskeleton contains fluorophores that emit blue-greenish fluorescence under ultraviolet radiation. Although there are some reports in the literature on the study of fluorescence in scorpions, the biological functionality of this light emission is currently unknown and is under debate. In this work, the properties of emission from the scorpion's exoskeleton are studied by means of digitally processed photographs taken of living specimens under ultraviolet illumination and complemented with standard spectroscopic measurements of emission and excitation spectra. With the aim of identifying possible correlations between the fluorescence, the characteristics color of the exoskeleton and the biology of the scorpions, 4 families, 9 genera and 24 species were studied. Our results suggest that the intensity of fluorescence is heterogeneous throughout the scorpion's exoskeleton studied here in such a way that pedipalps and metasomal segments fluoresce more intensely than the mesosomal segments. The spectrum of fluorescence across species is practically identical, suggesting that the same fluorophores are present in their exoskeletons. However, the fluorescence intensity emitted by each species varies according to their characteristic color (associated with the exoskeleton optical reflectance). Since the coloration of the exoskeleton is determined by the concentration of melanin and other pigments according to the substrate where scorpions live in, we conclude by suggesting that fluorescence may correlate directly to the ecomorphotype of the scorpions.

Reference:
López-Cabrera D, Ramos-Ortiz G, González-Santillán E, Espinosa-Luna R. Characterization of the fluorescence intensity and color tonality in the exoskeleton of scorpions. Journal of Photochemistry and Photobiology B: Biology. 2020;209:111945. [Subscription required for full text]

Thanks to Edmundo González Santillán for sending me their article!

 

More on scorpion fluorescence

Is scorpion fluorescence just an evolutionary accident or a genius adaption to scorpion life?

The mystery of scorpion fluorescence under UV-light have been under research in the last decade. Theories range from having no behavioral purpose to causing scorpions to be "living eyes". I have written several posts on the blog in the last couple of years on these theories.

This time Douglas Gaffin and Tristan Barker present a study on how scorpions react to different levels of UV irradiance. The study demonstrates that scorpions respond differently to different UV levels experienced during normal activity time and that locomotor activity was strongest when at UV irradiance levels that corresponded to sunset (the time scorpions move to the threshold of their burrows).

This study does indicate that scorpions are able to detect UV-levels, but more research is needed to demonstrate whether scorpion fluorescence has an adaptive function in UV-detection.

Abstract:
Scorpions are nocturnal arachnids that fluoresce a bright cyan-green when exposed to UV light. Although the function of this fluorescence remains unknown, some authors have suggested that it may aid the scorpions’ light detection. Taking advantage of scorpions’ negatively phototactic behavior, we tested the responses of desert grassland scorpions, Paruroctonus utahensis (Williams 1968), to 395 nm UV light at irradiances corresponding to an hour before sunset (0.15 mW/ cm2), sunset (0.01 mW/cm2), and moonlight (0.0001 mW/cm2), as well as no light. We found that animals showed the strongest responses to UV light levels equivalent to sunset. The animals moved more quickly and sporadically under the higher light levels. In addition, animals were less likely to complete a trial under highest light conditions, suggesting that UV light may inhibit normal scorpion locomotion. Finally, this study resulted in several methodological refinements, including automated tracking of the subjects’ movements that should prove useful in future behavioral studies of scorpion phototactic behavior.

Reference:
Barker TN, Gaffin DD. Comparison of scorpion behavioral responses to UV under sunset and nighttime irradiances. Journal of Arachnology. 2014;42(1):111-8. [Free Open Access Article]

Scorpions in the family Chaerilidae do not fluorescence under UV light

Scorpions fluorescence when they are exposed to ultraviolet light (in the range 320 - 400 nm). Several authors have discussed possible functions for this phenomena or if it has no function at all (previous blog posts on fluorescence).

Wilson Lourenco now reports that species in the family Chaerilidae do not fluorescence when exposed to UV light (Nine species were tested). This surprise finding is very interesting in the quest for any function of the fluorescence in scorpions. Interestingly, professor Lourenco also tested four species in the enigmatic family Pseudochactidae and they all did fluorescence. Pseudochactidae is considered to be the oldest and most primitive scorpion family and the presence of fluorescence may indicate that this is an early adaption in scorpions.

Abstract:
The fluorescence of scorpions in ultraviolet light, a well-known phenomenon, was discovered more than 60 years ago. Its possible function remains, however, a matter of discussion. Even during very recent studies, no conclusion has been reached. As suggested in these recent publications, the lack of or reduction of fluorescence could be a useful tool to explain the phenomenon. It is suggested here that, in at least some species of the family Chaerilidae Simon, this phenomenon is absent. This new discovery may initiate important comparative eco-physiological studies.

Reference:
Lourenço WR. Fluorescence in scorpions under UV light; can haerilids be a possible exception? Comptes Rendus - Biologies. 2012;335:731-4. [Subscritpion required for full text]

Thanks to professor Wilson Lourenco for sending me his paper!

Scorpions - Walking eyes?

Happy New year to you all!

The reason for the cryptic title of this post is a recent paper by Douglas Gaffin and co-workers in Animal Behaviour on the mystery of scorpion fluorescence.

There have been many theories on why scorpions fluorescence when exposed to UV-light. One theory is that this phenomena has no behavioral function and that the fluorescing components are just metabolic byproducts. Alternatively, scorpion fluorescence has a function (e.g. as a prey lure, as an aposematic signal or as an aid in the recognition of conspecifics (mate finding)). Some theories has been tested and rejected, but fluorescence in scorpions is still a mystery.

Gaffin and co-workers have tested scorpion activity under different light wavelengths (including UV-light) with eyes covered or not. The results suggest that scorpion cuticular fluorescence actually may be involved in their perception of light and contributes to orientation and light-avoidance behavior (e.g. helps the decision to stay in their burrow until outside light conditions are optimal for avoiding predators etc.).

This paper says that in addition to medial and lateral eyes, the metasomal elements that are sensitive to green light, the skin of the scorpion actaully works as an extra gigant eye helping in sensing light and detecting shadows. More studies are of course necessary before this theory is confirmed, but this is another proof of how fantastic animals scorpions are.

Abstract:
Scorpions are largely solitary, nocturnal arachnids that glow a bright cyan-green under UV light. The function of this fluorescence is a mystery. Previous studies of four species from three families have shown that scorpion lateral and medial eyes are maximally sensitive to green light (around 500 nm) and secondarily to UV (350e400 nm). Scorpions are negatively phototactic, and we used this behaviour to assay the responses of desert grassland scorpions, Paruroctonus utahensis, to 395 nm UV light, 505 nm cyan-green light, 565 nm green light and no light within small, circular arenas. Based on the eye sensitivity data, we predicted maximal response to 505 nm, followed by lower responses to 395 and 565 nm. In our experiments, however, scorpions responded most intensely (abrupt bouts of locomotory activity) to 395 nm and 505 nm. Next, we ran trials under 395 and 505 nm on scorpions with their eyes blocked. Scorpions with blocked eyes were much less likely to move under 505 nm than under 395 nm and were much less likely to move under 505 nm than were control animals (those without their eyes blocked). These results suggest an active role for fluorescence in scorpion light detection. Other studies indicate that photosensitive elements in scorpion tails are sensitive to green light. We therefore propose that the cuticle may function as a whole-body photon collector, transducing UV light to cyan-green before relaying this information to the central nervous system. Scorpions may use this information to detect shelter, as blocking any part of the cuticle could diminish the signal.

Reference:
Gaffin DD, Bumm LA, Taylor MS, Popokina NV, Mann S. Scorpion fluorescence and reaction to light. Anim Behav. 2012. 83(2):429-436. Doi: 10.1016/j.anbehav.2011.11.014. [Subscription required for fulltext]

An interview with first author Douglas Gaffin about the paper can be found in Wired Magazine.

Thanks to Graeme Lowe for telling me about this paper!

Scorpion fluorescence - a way to avoid moonlight?

Scorpions fluorescence under UV-light. This is a great phenomenon for scorpion scientists and enthusiasts wanting to find and study scorpions, but its function has not been known so far. Suggested functions have been uv-light detection, mate identification, species identification, luring of prey, light amplification and that the fluorescence has no fuction at all.

Carl Kloock has written several papers on scorpion fluorescence (previous blog post), and in his latest paper (authored together with Abraham Kubli and Ricco Reynolds) it is concluded that their experimental data support the hypothesis that scorpion fluorescence serves as a means for the detection of UV-light at very low levels. Further, it is suggested that the UV-light acts as a cue for moonlight avoidance (fluorescence is a way to detect the presence of uv-light which is correlated to a moonlit night and this cause the scorpions to stay hidden in their hidings).

This is the first experimental evidence for a potential function for scorpion fluorescence, but further studies are necessary before final conclusion can be made on this phenomenon.

Abstract:
The hypothesis that fluorescence in scorpions functions in the detection of ultraviolet light was tested. We reduced the fluorescence of scorpions by prolonged exposure to ultraviolet light on a 16:8 h light:dark cycle and compared their activity levels and light environment choices to unmodified scorpions in simple arenas that were half in shadow and half exposed to light. Three different lighting conditions were tested: infrared (IR) light only, IR + ultraviolet light and IR + white light. Treatments were illuminated by infrared light for videotaping. Activity level was measured by the number of transitions from the exposed to shadowed regions, and choice was measured by the percentage of time spent in the shadowed portion of the arena. Under IR + ultraviolet light, fluorescent scorpions reduced their activity levels and the variance in habitat choice increased, compared with reduced-fluorescence scorpions. There were no differences between fluorescent and non-fluorescent scorpions in the IR only condition or in the IR + white light condition. This is interpreted as evidence that fluorescence aids in the detection of and response to ultraviolet light, and possible implications of this result in natural habitats are discussed. This is the first experimental demonstration of a possible function for scorpion fluorescence.

Reference:
Kloock CT, Kubli A, Reynolds R. Ultraviolet light detection: A function of scorpion fluorescence. Journal of Arachnology. 2010;38(3):441-5. [Subscription required for fulltext, but free fulltext after 12 months]

Prolonged exposure to uv light reduces scorpion fluorescence

It is well known that scorpions fluorescence under ultraviolet light exposure. No function for this phenomena has yet been proven. It is possible that there is no biological function and that the fluorescence is a byproduct of a molecule whose primary function is unrelated to fluorescence. More research is necessary to unravel the mystery of scorpion fluorescence.

Anecdontal reports have suggested that long-term exposure to uv light may reduce scorpion fluorescence. Carl Kloock has recently published a paper showing that this is indeed true. Interestingly, Kloock's work also show that fluorescence in live specimens recovered after one week without uv exposure. This is an indication that active metabolic processes are responsible for the recovery. Preserved specimens with reduced fluorescence showed no recovery after termination of uv exposure.

Abstract:
No abstract available

Reference:
Kloock CT. Reducing scorpion fluorescence via prolonged exposure to ultraviolet light. Journal of Arachnology. 2009;37(3):368-70. [Free fulltext - Open Access article]