Download Scorpionism

Scorpionism, or envenomation caused by a scorpion sting, is a serious national public
health hazard that particularly affects regions like the Middle East, North Africa, West Asia,
South America, and Central America. Each year, an estimated 1.2 million incidents of scorpions’
sting take place around the world, with 3250 of them resulting in instant death. Scorpions use
their poisonous stinging mechanism and pedipalps to catch prey animals and deter predators.
Even though pedipalps and venom are found in all scorpions, the utilization is different across
species, reflecting a trade-off structure. It is a common perception that more venomous scorpion
species have lengthy, narrow chelae, such as several Buthidae species, but scorpion species such
as Opistopthalmus glabrifrons that have a stronger chela, also have a proportionally lessdeveloped stinging mechanism, a shorter metasoma, or less effective toxin overall. Despite the
overall prevalence of scorpionism, which is considerably greater owing to unidentified
envenomation incidents, the morphology and ecological history of scorpions and their toxin are
unexpectedly poorly understood. Thus, Forde and colleagues (2022) conducted a complex
phylogenetic comparative analysis study to determine the association between the
venom potency of the scorpions and their morphology and body size.
The authors explicitly stated the research hypothesis in the article i.e., smaller species of
scorpions with larger telsons and narrower chelae are more potent (indicated by lower LD50)
than larger scorpion species. To test this hypothesis, a thorough literature study was done by the
authors, and data was collected on the morphological characteristics and venom potency of
different scorpion species. The authors did an initial web search for data related to the
morphological characteristics and venom potency using keywords like "scorpion(s)", "scorpion
LD50", "telson measure”, “total body size", "pedipalp measure", and related terms. The median
lethal dose (LD50) was selected as a measure to assess venom potency while the width and the
length of the scorpion telson and chela along with their total body size were used as a measure to
assess scorpion morphological features. Next, for comparatively analyzing the data collected
from a comprehensive literature study, the body size and LD50 values were transformed to log10,
so that the model residuals could show a more normal distribution. Furthermore, the hypothesis
was tested with the help of the Bayesian phylogenetic mixed models (BPMM), using the
MCMCglmm package, which allows the study of the relationship among different explanatory
variables and variant terms. The following figure 1 illustrates the working procedure utilized by
the scientists to test their developed hypothesis.
Hypothesis
Literature Review
Comparative Analysis
Smaller species of scorpions with larger telsons and narrower
chelae are more potent (indicated by lower LD50) than larger
scorpion species
To test the hypothesis, a thorough literature study was done,
and data was collected on the morphological characteristics
and venom potency of different scorpion species
For comparatively analyzing the collected data, the body sized
and LD50 were transformed to Log 10, and then the hypothesis
was tested with the help of Bayesian phylogenetic mixed
models (BPMM), using the MCMCglmm package.
Figure 1: an illustration of the working procedure utilized by the scientists to test their
developed hypothesis
The dataset used by Forde and colleagues (2022) included 36 scorpion species and 62
LD50 measurements, all of which matched their inclusion criteria based on mammalian Mus
musculus models. The dataset lethality values ranged from 0.16 mg/kg (shown by the
deathstalker Leiurus quinquestriatus specie) to 1800 mg/kg (shown by the rock scorpion
Hadogenes granulatus specie). The dataset body size values ranged from 40.5 mm to 200 mm,
depicted by the bark scorpion Scorpion Centruroides noxious and H. granulatus, respectively.
The median body size value of scorpions was found to be 70 mm. Moreover, the chela ratio in
the dataset varied bet ween 0.7 and 6.2. The narrowest chelae were observed in the
deathstalker Leiurus quinquestriatus while the strongest chelae were identified in the red
scorpion Rhopalurus junceus and the large-clawed scorpion Scorpio maurus. Dataset analysis
results (as shown in the following figures) revealed that a positive association exists between the
body length and LD50 values whereas a negative association exists between the chelae ratio
(morphological traits) and LD50 values.
Figure 2: For 62 LD50 measures spanning over 36 scorpion species, the figure shows an
association between log10 total length (mm) and log10 LD50 (mg/kg). The fitted line, corrected for
the median chelae ratio value of 3.7, shows a strong positive connection between log10 total
length and log10 LD50. The hollow yellow circles highlight the following species, which are
indicated from right to left as Hadogenes granulatus; Androctonus crassicauda; Scorpio maurus;
Scorpion Centruroides noxius; Hadogenes granulatus; Parabuthus transvaalicus; Androctonus
crassicauda.
Figure 3: For 62 LD50 measures spanning over 36 scorpion species, the figure shows an
association between chelae and log10 LD50 (mg/kg). The fitted line, corrected for the median
log10 total length value of 70 mm, shows a strong negative association between the chelae ratio
and log10 LD50. The hollow red circles highlight the following species, which are indicated from
right to left as Parabuthus transvaalicus, Scorpion Centruroides noxius, Hadogenes granulatus;
Scorpio maurus.
Thus, the study results significantly support the commonly accepted belief that smaller
scorpion species with narrower chelae are more lethal as compared to bigger scorpions with
stronger chelae. For instance, in the selected data set, the rock scorpion Hadogenes.
granulatus, which is the largest species in the study, has the lowest toxic venom. Likewise,
scorpions with large, robust chelae, including the Israeli gold scorpion Scorpio maurus, were
linked to venoms that were relatively weak. The venoms of scorpions with thin chelae, like the
South African thick-tail scorpion Parabuthus transvaalicus, were found to be more potent.
To sum it all up, the study conducted by Forde and colleagues (2022) significantly
contributes to the field of research by verifying the association between scorpion body size and
venom toxicity. This study assists in recognizing the evolutionary and ecological determinants
of venom potency of scorpions, which along with providing a basic understanding of scorpion
species enables the individuals to handle the widespread scorpionism problem. Thus, this study
empowers future researchers to address the issue of scorpionism based on venom potency and
body size. However, the authors could have improved the study by evaluating the association of
more scorpion morphological features like the metasoma with venom potency. This could have
improved the results and provided a bigger picture as the metasoma thickness is also found to be
associated with venom toxicity. Moreover, this could have also pointed to a link between the
frequency with which a species uses venom and the assertion that organisms that depend on
toxins for preying need more developed metasoma.
Reference
Forde, A., Jacobsen, A., Dugon, M. M., & Healy, K. 2022. Scorpion Species with Smaller Body
Sizes and Narrower Chelae Have the Highest Venom Potency. Toxins. 14(3): 219.