Differences in sprinting performance between burrowing and non-burrowing scorpions

 

Scorpions are different. Some move quickly, others more slowly. Some make burrows and stay there most of the time, while others are more active on the surface and hide under suitable objects during daytime. Eran Gefen and co-workers have recently published a study where they tested the endurance of three Israeli buthids and two scorpionids. 

The study showed that buthids are fast runners, but they tire more quickly. The burrowing scorpionids are slower, but show more endurance. The authors discuss the physiology behind these differences. The faster sprinting speed in buthids are probably an adaption to escaping predators, while the endurance seen in scorpionids is probably an adaption for digging deep burrows over a longer time.

Please note that there is a correction published for this article (it is available on the article's main page). 

Abstract:
Aerobic capacity in arachnids is closely linked with considerable structural variation in their respiratory systems. However, although all scorpions are non-tracheated and possess four pairs of book lungs, they vary greatly in their locomotor activity patterns. Many nonburrowing species express short bursts of activity whereas other species dig deep burrows within hours, suggesting more aerobically fueled exercise.We hypothesized that locomotion in surface dwellers is more dependent on anaerobic ATP synthesis, and that this would be reflected in their exercise performance and functional adaptation to potential disturbance of resting-state homeostasis. We used an experimental design consisting of two surface-dwelling Buthidae species (Hottentotta judaicus and Leiurus hebraeus), a burrowing buthid (Buthus israelis) and two burrowing Scorpionidae (Scorpio fuscus and Scorpio palmatus). Maximum running speeds were higher for buthids, which were also more prone to fatigue than scorpionids. Higher respiratory exchange ratios recorded for buthids during activity and subsequent recovery indicated a higher reliance on anaerobically fueled locomotion compared with scorpionids. Our data show that quicker removal of excess CO2 resulting from anaerobic exercise and hemolymph buffering in buthids is associated with significantly higher carbonic anhydrase activity in their hemolymph, compared with that of scorpionids. Efficient CO2 emission may also contribute to the lower respiratory water losses of buthids, and thus assist in facing both biotic and abiotic challenges of surface existence, from which the scorpionid burrows provide refuge.

Reference:
Gefen E, Atiya S, David LM, Talal S. Sprinting performance is linked to surface activity in scorpions. J Exp Biol. 2026;229:jeb251978. [Open Access]

Thanks to Matt Simon for informing me about this article and for his comments about it. 

Do hot temperatures cause hot tempered scorpions?

 

Scorpions are dependent on the temperatures in its environment to regulate their body temperatures (being ectothermic) and they will probably also have an effect on scorpion behavior. Scorpions use their sting and venom in prey capture and defense. 

Zia Nisani and co-workers have recently published a study looking into if and how different temperatures impact stinging behavior in Hadurus obscurus Williams, 1970 (Hadruridae). They tested how different temperatures impacted the defensive sting response and also the prey capture behavior at three different temperatures.

Scorpions with higher temperatures were faster to sting and required less provocation before stinging. In addition, "hotter" scorpions were quicker to catch prey and succeed with it. A physiological explanation for these results is probably that increased temperatures will increase muscle performance and metabolic rate. 

Abstract:
Scorpions employ their stinging mechanism both for defense and predation, and being ectothermic, temperature influences their physiology and behavior. As such, we hypothesized that temperature both affects defensive stinging and prey-capture behavior in scorpions. We tested the effects of body temperature on these behaviors in the desert hairy scorpion, Hadrurus obscurus Williams, 1970. In the first experiment, scorpions were placed in temperature-controlled chambers with either high (26-28°C) or low (21-22°C) temperatures and probed to elicit a defensive sting. We recorded the reaction time and the number of probes needed to elicit a sting. In the second experiment, we observed and recorded prey capture behavior at three different temperatures (21, 29, and 33°C). Scorpions with higher body temperatures had faster defensive reaction times and required fewer probes to elicit a sting. Furthermore, at a higher temperature, scorpions were more likely to attempt and succeed in prey capture, but temperature did not seem to affect post-capture stinging behavior. As the temperature rises, increasing muscle performance and metabolic rate in ectotherms, it may cause an increase in prey capture attempts and faster reaction times, as observed in our experiment. These results support our hypothesis that both defensive and predatory behavior in H. obscurus is affected by temperature, allowing more insight into scorpion thermal ecology.

Reference:
Nisani Z, Bennett M, Enriquez A, Iniquez M, Martinez Rios E, Stone B. Effect of temperature on the defensive and predatory behavior of the scorpion Hadrurus obscurus (Scorpiones: Hadruridae). Euscorpius. 2026;2026(433):1–9. [Open Access]

Physiological adaptions in winter active species of Urophonius

 

Scorpions are mainly known from warm regions and their adaptions to arid habitats are well studied. Less known and studied are scorpions that inhabit high altitudes or other habitats that experience sub-zero temperatures during the year. A special case among these are the two species Urophonius achalensis Abalos & Hominal, 1974 and U. brachycentrus (Thorell, 1876) (Bothriuridae) from Argentina that are unusual in that they actually are active during the winter (in periods with sub-zero temperatures).

C.Fernando Garcia and co-workers published last year a study investigating the possible physiological adaptations to different temperatures in the two winter active bothriurids. Their main conclusion is that the acclimatization to cold generates important lipidic metabolic variations in different organs and tissues.

Abstract:
Different organisms (mainly poikilotherms) are subject to environmental fluctuations that could affect their normal physiological functioning (e.g., by destabilization of biomembranes and rupture of biomolecules). As a result, animals regulate their body temperature and adapt to different environmental conditions through various physiological strategies. These adaptations are crucial in all organisms, although they are more relevant in those that have reached a great adaptive diversity such as scorpions. Within scorpions, the genus Urophonius presents species with winter activity, being this a peculiarity within the Order and an opportunity to study the strategies deployed by these organisms when facing different temperatures. Here, we explore three basic issues of lipid remodeling under high and low temperatures, using adults and juveniles of Urophonius achalensis and U. brachycentrus. First, as an indicator of metabolic state, we analyzed the lipidic changes in different tissues observing that low temperatures generate higher quantities of triacylglycerols and fewer amount of structural lipids and sphyngomielin. Furthermore, we studied the participation of fatty acids in adaptive homeoviscosity, showing that there are changes in the quantity of saturated and unsaturated fatty acids at low temperature (mainly 16:0, 18:0, 18:1 and 18:2). Finally, we observe that there are quantitative and qualitative variations in the cuticular hydrocarbons (with possible water barrier and chemical recognition function). These fluctuations are in some cases species-specific, metabolic-specific, tissue-specific and in others depend on the ontogenetic state.

Reference:
Garcia CF, Oviedo-Diego M, Laino A, Peterson G, Mattoni CI, Peretti AV, et al. Low temperatures induce physiological changes in lipids, fatty acids and hydrocarbons, in two rare winter scorpions of genus Urophonius (Scorpiones, Bothriuridae). J Therm Biol. 2021;96. [Sunscription required for full text]

Thanks to Andres Ojanguren-Affilastro for sending me their article!

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!

 

Tityus serrulatus - A natural born killer

A very tabloid headline for this post, but I felt I couldn't plagiarize the nice original article title "Selected to survive and kill". Scorpion stings in Brazil have increased in the last decade and the main culprit has been Tityus serrulatus Lutz and Mello, 1922 (Buthidae). This very invasive species has spread in Brazil in the last decades and has adapted very well to urban habitat. In addition, the species can reproduce by parthenogenesis, making this species a very expanding taxa.

Ricardo Jose Gonzaga Pimenta and co-workers have recently published a study on how well Tityus serrulatus handles food and water deprivation. The authors found that this medical important scorpion has an impressive capacity to survive starvation for long periods. Lack of water, on the other hand, caused a large decrease in survival rates. Reproduction occurred throughout the year for food-deprived scorpions and controls, but not in the water-deprived groups.

The results of this study have implications for how scorpion control should be conducted for this expanding, hard to kill, dangerous species in urban areas.

Abstract:
Annually, more than 1.2 million scorpion stings and more than 3,000 deaths occur worldwide. Tityus serrulatus Lutz and Mello, 1922 (Scorpiones, Buthidae) is the most medically relevant species in Brazil where it is spreading rapidly and causing over 90,000 cases of envenomation yearly. We monitored T. serrulatus longevity and ability to reproduce under conditions of food and/or water deprivation. We found that T. serrulatus is highly tolerant to food deprivation, with individuals enduring up to 400 days without food. On the other hand, access to water played a pivotal role in T. serrulatus survival. Food and water deprived scorpions showed weight reduction. Reproduction occurred throughout the year for fooddeprived scorpions and controls, but not in the water-deprived groups. Remarkably, fooddeprived animals were able to give birth after 209 days of starvation. Tityus serrulatus resistance to food and water deprivation is likely to be an additional factor underlying this species’ geographic expansion and the difficulties encountered in controlling it.

Reference:
Pimenta RJG, Brandao-Dias PFP, Leal HG, Carmo AOD, Oliveira-Mendes BBR, Chavez-Olortegui C, et al. Selected to survive and kill: Tityus serrulatus, the Brazilian yellow scorpion. PLoS One. 2019;14(4):e0214075. [Open Access]

Thanks to Matt Simon for informing me about this article!

A new review on scorpion envenomation

Pathophysiological and clinical effects of systemic scorpion envenomation. Isbister & Bawaskar/New England Journal of Medicine, 2014 (C).

With more than one million cases of scorpion envenomation each year worldwide with substantial morbidity and even death in children, scorpions pose a health challenge in many countries. Geoffrey Isbister and Himmatrao Bawaskar have recently published a updated review on the effects of scorpion envenomation and the current treatment knowledge in the top medical journal New England Journal of Medicine.

This article is essential for health personnel dealing with scorpion envenomation patients, scorpion researchers and others interested in scorpions as it sums up symptoms, pathophysiology, clinical manifestations and treatment for scorpion envenomations.

Abstract:
Scorpion stings and envenomation are of clinical importance worldwide, and although most stings cause only local effects, severe envenomation that causes either excessive autonomic activity and cardiovascular toxic effects or neuromuscular toxic effects results in illness and, in the case of children, in death. The specific treatment is the administration of antivenom combined with symptomatic and supportive treatment, including prazosin and dobutamine in patients with cardiovascular toxic effects and benzodiazepines when there is neuromuscular involvement.

Reference:
Isbister GK, Bawaskar HS. Scorpion Envenomation. N Engl J Med. 2014;371(5):457-63. [Subscription required for full text]

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!

Metabolic cost of venom regeneration and venom complexity in Parabuthus transvaalicus

It has previously has been showed that venom use is costly, both in terms of metabolic and ecological costs (Nisani et al, 2007; Nisani, 2008), that some scorpions have two types of venom with different composition (and different "production costs") (Inceoglu et al., 2003) and that Parabuthus transvaalicus Purcell, 1899 (Buthidae) are able to regulate venom use at different levels (Click here for more information).

Zia Nisani and co-workers have now further confirmed the relatively high cost of venom regeneration and also have shown that greater venom complexity can be associated with higher cost of venom production.

Abstract:
We investigated the biochemical profile of regenerated venom of the scorpion Parabuthus transvaalicus in relation to its metabolic cost and toxicity. Using a closed-system respirometer, we compared oxygen consumption between milked and unmilked scorpions to determine the metabolic costs associated with the first 192 h of subsequent venom synthesis. Milked scorpions had a substantially (21%) higher mean metabolic rate than unmilked scorpions, with the largest increases in oxygen consumption occurring at approximately 120 h, 162 h, and 186 h post-milking. Lethality tests in crickets indicated that toxicity of the regenerated venom returned to normal levels within 4 d after milking. However, the chemical profile of the regenerated venom, as evaluated by FPLC and MALDITOF mass spectrometry, suggested that regeneration of different venom components was asynchronous. Some peptides regenerated quickly, particularly those associated with the scorpion’s “prevenom,” whereas others required much or all of this time period for regeneration. This asynchrony could explain the different spikes detected in oxygen consumption of milked scorpions as various peptides and other venom components were resynthesized. These observations confirm the relatively high metabolic cost of venom regeneration and suggest that greater venom complexity can be associated with higher costs of venom production.

Reference:
Nisani Z, Boskovic DS, Dunbar SG, Kelln W, Hayes WK. Investigating the chemical profile of regenerated scorpion (Parabuthus transvaalicus) venom in relation to metabolic cost and toxicity. Toxicon. 2012;60(3):315-23. [Subscription required for full text]

Sting use, risk assessment and control of venom used in Parabuthus transvaalicus

One of the conclusions from my master thesis many years ago was that sting use is probably costly for scorpions and because of this they will only use their stinger if the prey is large and/or the prey resists capture. My study was based on an assumption that use of venom in scorpions was costly and also that scorpions were able to control both the use of the stinger and of the venom. And now it seems that my assumptions were correct :)

Since then, it has been showed that venom use is costly, both in terms of metabolic and ecological costs (Nisani et al, 2007; Nisani, 2008). It has also been demonstrated that some scorpions have two types of venom with different composition (and different "production costs") (Inceoglu et al., 2003).

Now Zia Nisani and Wlliam Hayes have shown that Parabuthus transvaalicus Purcell, 1899 (Buthidae) are able to regulate venom use at three levels:

• They can choose between a dry and a wet sting (use of venom).
• When using when om they can control the volum of venom expended, delivering more venom under hight threat and less volum under low threat conditions.
• They can vary the composition of the venom injected, either using "cheap" prevenom or the more potent protein rich venom.

All of the above results support the hypothesis that scorpions display a venom optimization strategy by regulating venom expenditure based on the level of perceived threat.

This is a great paper that I reccomend to all that are interested in scorpion behavior and scorpion's adaption to their environment!

Abstract:
Venom is a metabolically expensive commodity that animals should use judiciously. The venommetering hypothesis proposes that venomous animals control, or meter, the quantity of venom they deploy during predatory or defensive situations.We sought to clarify experimentally whether the buthid scorpion Parabuthus transvaalicus can regulate defensive venom expenditure based on perceived risk. Scorpions were tested under two threat conditions by inducing them to sting repeatedly a parafilmcovered cup. The high-threat condition involved five sting presentations at 5 s intervals, and the lowthreat condition comprised five sting presentations at 5 min intervals. Venom metering appeared to be modulated at three levels: wet versus dry sting, composition of venom injected and volume of venom delivered. Scorpions delivered dry stings more often under the low-threat condition, but in both conditions were more likely to employ wet stings as the threat persisted. Venom appearance changed during successive stings from clear (potassium-rich ‘prevenom’), to opalescent, to milky (protein-rich ‘venom’), with biochemical analyses (protein assay and MALDI-TOF) confirming the compositional changes. However, progression through this sequence depended on quantity of venom expended, with milky secretion appearing only after the limited quantity of clear secretion was exhausted (i.e. composition and volume covaried). Scorpions injected approximately two-fold more venom per sting during the high-threat compared to the low-threat condition, with milky venom appearing more quickly within the sequence of five stings for the high-threat condition. Thus, these scorpions perceive risk and regulate venom expenditure during stinging according to level of threat, providing further support for the venommetering hypothesis.

Reference:
Nisani Z, Hayes WK. Defensive stinging by Parabuthus transvaalicus scorpions: risk assessment and venom metering. Anim Behav. 2011;81(3):627-33. [Subscription required for fulltext]

Other references mentioned:
Inceoglu B, Lango J, Jing J, Chen L, Doymaz F, Pessah IN, et al. One scorpion, two venoms: Prevenom of Parabuthus transvaalicus acts as an alternative type of venom with distinct mechanism of action. Proc Natl Acad Sci U S A. 2003;100(3):922-7.

Nisani Z, Dunbar SG, Hayes WK. Cost of venom regeneration in Parabuthus transvaalicus (Arachnida: Buthidae). Comp Biochem Physiol A Mol Integr Physiol. 2007 Jun;147(2):509-13.

Nisani Z. Behavioral and physiological ecology of scorpion venom expenditure: stinging, spraying, and venom regeneration: Loma Linda University; 2008 (Ph.D. thesis).

Water loss in scorpions

Scorpions are known for low metabolic rates and low water loss rates. Previously, we have learned that mesic and/or burrowing species have had lower water loss rates than xeric species due to a life in a "better" microclimate. A new study shows that it ain't necessarily so.

Eran Gefen have now published a very interesting study investigating how the relative importance of respiratory water loss is correlated with species habitat type and activity pattern, using both xeric and mesic and burrowing and non-burrowing species. Also, Gefen's study has an improved experimental design placing the scorpions in a more realistic situation during experiments and thereby getting more realistic data for water loss and metabolic rates.

A summery of the results and conclusions can be seen in the abstract below.

Abstract:
Scorpions exhibit some of the lowest recorded water loss rates compared with those of other terrestrial arthropods of similar body size. Evaporative water loss (EWL) includes cuticular transpiration and respiratory water loss (RWL) from gas exchange surfaces, that is, book lung lamellae. Estimated fractions of cuticular and respiratory losses currently available from the literature show considerable variation, at least partly as a result of differences in methodology. This study reports RWL rates and their relative importance in scorpions from two families (Buthidae and Scorpionidae), including both xeric and mesic species (or subspecies). Two of the included Buthidae were surface-dwelling species, and another inhabits empty burrows of other terrestrial arthropods. This experimental design enabled correlating RWL importance with scorpion phylogeny, habitat type, and/or homing behavior. Buthidae species exhibited significantly lower EWL rates compared with those of Scorpionidae, whereas effects of habitat type and homing behavior were not significant. Resting RWL rates were not significantly affected by scorpion phylogeny, but rates for the xeric species (totaling ∼10% of EWL rates at 30 C) were significantly lower compared with those of mesic species. These lower RWL values
were correlated with significantly lowerH2O/CO2 emission rates in xeric species. The experimental setup and ∼24-h duration of each individual recording allowed estimating the effect of interspecific variation in activity on RWL proportions. The high respiratory losses in active hydrated Scorpio maurus fuscus, totaling 30% of EWL, suggest that behavioral discretion in this species is a more likely mechanism for body water conservation under stressful conditions when compared with the responses of other studied species.

Reference:
Gefen E. The Relative Importance of Respiratory Water Loss in Scorpions Is Correlated with Species Habitat Type and Activity Pattern. Physiol Biochem Zool. 2010 Nov 19. [Published ahead of print] [Subscription required for fulltext]

Thanks to Dr. Gefen for sending me 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]

Water loss in scorpions living in arid environments

Scorpions are very common in many arid areas and many species are well adapted to a life in areas with high temperatures and low precipitation. One of the main adaptions to life in such harsh environments is to reduce loss of body water. Body water is lost to the environment mainly through the skin (cuticular water loss) and through respiration (respiratory water loss). In scorpions, the main loss of body water is through the respiration.

A recent study by Gefen, Ung & Gibbs (2009) looks into water loss in the North American species Hadrurus arizonensis (Caraboctonidae). See abstract for details about the study and its results.

Abstract:
Terrestrial arthropods lose body water to the environment mainly through transpiration. The aim of this study was to determine the fraction of respiratory losses from total transpiratory water loss in scorpions, as relatively high respiratory losses would indicate a fitness benefit from regulation of gas-exchange rate under stressful desiccating conditions. We measured metabolic rates and water-loss rates of Hadrurus arizonensis (Iuridae) at a range of ecologically-relevant temperatures. Calculation of respiratory water losses was based on increased metabolic and water-loss rates during nocturnal activity (assuming no change in cuticular resistance at a given constant experimental temperature). Respiratory losses accounted for 9.0 ± 1.7% of total transpiratory losses at 25 °C, doubled to 17.9 ± 1.8% at 30 °C and increased to 31.0 ± 2.0% at 35 °C (n = 5, 15 and 15, respectively). Furthermore, the relative importance of respiratory transpiration is likely to be higher at temperatures above 35 °C, which have been recorded even within the burrows of H. arizonensis. Measurements of cuticular lipid melting points do not provide evidence for increased cuticular resistance to water loss at higher temperatures. However, the relatively high fraction of respiratory water losses reported here for H. arizonensis supports the notion of respiratory regulation as an evolved mechanism for conserving scorpion body water stores under stressful conditions.

Reference:
Gefen E, Ung C, Gibbs AG. Partitioning of transpiratory water loss of the desert scorpion, Hadrurus arizonensis (Iuridae). J Insect Physiol. 2009 Jun;55 (6):544-8. [Subscription required for fulltext]

Family Caraboctonidae

Are female scorpions better desert survivors than males?

It is well known that desert scorpions are among the best adapted arthropods inhabiting the warm and dry deserts of the world. Scorpions exhibit some of the lowest water-loss rates recorded for arthropods, and also have strategies for either tolerating increased haemolymph osmolarity or regulating the volum and consentration of the body fluid.

In a recent paper, Gefen (2008) shows that female Smeringurus mesaensis (Vaejovidae) actually is better than males in handling the though conditions in a desert environment. The females had larger hepatopancreas compared to males, and showed a considerably better osmoregulatory capacity. Females had higher hepatopancreas water content and higher mobilization rates of water from the hepatopancreas to the haemolymph during deccication.

Here is the abstract from the article:

The osmoregulatory and respiratory responses of male and female Smeringurus mesaensis (Vaejovidae) to prolonged desiccation were measured. No significant effect of sex on mass-loss rates (MLRs) was found. Still, females maintained their haemolymph osmolality when desiccated to 10% mass loss, whereas that of males increased significantly after loss of as little as 5% of initial mass. Females had a 3-fold larger hepatopancreas, significantly higher hepatopancreas water content and higher metabolic rates when adjusted to hepatopancreas-free dry mass. Thus, females not only store more water in the hepatopancreas but also mobilise it to the haemolymph at a higher rate during desiccation, thus maintaining haemolymph osmolality.

Gas exchange rates of both males and females decrease as desiccation progresses. An initial respiratory exchange ratio (RER) of 0.9 is followed by a significant increase at mass loss levels of 7.5% and higher. RER values greater than 1.0 may result from partial shift to anaerobic catabolism, which allows closure of the book lung spiracles for longer duration, thus minimising respiratory water loss.

The effects of gas exchange rates on rates of water mobilisation between body compartments and water loss to the environment suggest a trade-off between maintaining osmotic stability and conserving body water stores under stressful conditions.

Reference:
Gefen E. Sexual dimorphism in desiccation responses of the sand scorpion Smeringurus mesaensis (Vaejovidae). J Insect Physiol. 2008;54(5):798-805. [Subscription required for fulltext]