Sex differences in morphology cause sex differences in stridulation in the buthid Jaguajir rochae

 

It is not that well known that scorpions can produce sound that probably is meant to function defensively as an anti-predator defense. The sound is often called stridulation, and in scorpions it can be produced by morphological structures on the chelicera, legs, cauda or pectines.

Welton Dionisio-da-Silva and co-workers have recently published a study on stridulation Jaguajir rochae (Borelli, 1910) (Buthidae) and any sex-differences in the morphology of the sound producing structures and the acoustic output.

They found that there were several differences in the morphology of the sound producing structures of the pectins between the sexes, and they also found that females produced longer and more intense signals while the males exhibited slightly higher peak frequencies.

Abstract:
Stridulation, acoustic communication produced by friction between specialized body structures, is a poorly studied antipredator mechanism. Scorpions may display multiple defensive responses, yet acoustic signaling in such defensive context remains poorly studied. Given the sexual dimorphism commonly observed in scorpion body size and pectines, the latter, which may be involved in sound production, could vary morphologically and result in acoustic differences. We hypothesized that (1) stridulatory apparatus of the scorpion Jaguajir rochae (Borelli, 1910) is sexually dimorphic, (2) sexual dimorphism in stridulatory structures affects acoustic parameters, and (3) stridulatory responses vary with stress, tested via (2.1) mechanical and (2.2) mechano-chemical stimulation. Sound-producing structures and acoustic parameters were measured and stridulation was tested under high/low mechanical stress and mechano-chemical stress, the latter using chemical cues from a mammalian predator. Females exhibited larger pectinal structures, whereas males showed a higher allometric ratio relative to body size. Stridulatory signals in J. rochae showed sexual differentiation primarily in delta time, dB Sound Pressure Level, and low frequency, as revealed by Principal Component Analysis, what explains 38.7% of acoustic variance. Females produced longer and more intense signals, whereas males exhibited slightly higher peak frequencies. Yet, the occurrence of stridulatory responses was similar across different stress treatments. These findings reveal that sexual dimorphism in stridulatory apparatus influences acoustic parameters and that stridulation in J. rochae can be triggered by mechanical stimulation, supporting its role as a defensive behavior. This study provides the first evidence of sex specific acoustic variation in scorpion stridulation and elucidates its function as an antipredator strategy.

Reference:
Dionisio-da-Silva W, Luna NMC, da Rocha PA, Willemart RH, daSilva MB. She Doesn't Whisper: Female-Prominent Stridulation Shaped by Morphology in a Buthid Scorpion and Insights on Its Function. Ethology. 2026;First published 25.05.26. [Open Access]

Using chemical cues to avoid intraguild predators and to find potential mates

 

It is well known that scorpions can detect and use chemical cues thanks to chemosensitive hairs on the pectins and on part of the pedipalps. Chemical cues can be used to discover and seek out conspecifics for mating, but also to avoid conspecifics or other scorpions that want to eat you (cannibalism is well documented in scorpions, often larger individuals preying on smaller and larger females may also kill and eat potential suitors).

Welton Dionisio-da-Silva and co-workers published earlier this summer a study of the use of chemical cues in the two Brazilian scorpions Bothriurus rochai Mello-Leitão, 1932 (Bothriuridae) and Jaguajir rochae (Borelli, 1910) (Buthidae). They tested the behavioral response to chemical cues from a heterospecific scorpion, and the response of male individuals (B. rochai and J. rochae) to chemical cues from conspecific females.

The study showed that smaller individuals avoided sites with the "smell" of larges individuals, whiles larger predators preferred the sites with the "smell" of smaller scorpions. In addition, males of both species trailed the chemical cues of females. 

According to the authors, this is the first evidence of a scorpion species detecting and hunting a heterospecific scorpion through chemical cues.

Abstract:
Chemical perception is essential among arthropods for mate recognition, prey search, and predator avoidance, especially for solitary predators which are often aggressive. Such mechanisms may be intensified in environments like the Caatinga, a seasonally dry tropical forest in Brazil, characterized by low habitat complexity and high seasonal variation. Thus, we investigated chemical perception between two scorpion species from this environment, involved in intraguild competition. Experiments assessed their response to chemical cues from prey, predators, and potential mates. We use Y-mazes to test the time spent by the scorpions between Y-arms with or without a given substrate-borne chemical cue (site preference) and the number of active individuals during trials (presence of activity). Scorpions’ activity was not influenced by chemical stimuli, although they clearly exhibit site preferences. The smaller predators avoided sites with the larger species’ chemical cues, while the larger predators preferred sites with the smaller species’ cues. Additionally, both species trailed female chemical cues. These findings suggest a dual-oriented arms race where prey and predator modulate their behaviour to avoid and hunt heterospecifics, respectively. This study provides the first evidence of a scorpion using chemical cues to detect a heterospecific scorpion and highlights the importance of this trait in arachnids.

References:
Dionisio-da-Silva W, Araujo Rocha-da-Silva KL, Veloso HMG, DaSilva MB. Hide and seek: chemical cues drive site preference among potential mates and intraguild competitors. Biological Journal of the Linnean Society. 2024:blae058. [Subscription required for full text]

Thanks to Welton Dionisio-da-Silva for sending me their article!

 

A fatal case of Jaguajir rochae scorpion sting in Brazil due to allergic reaction

Death and serious morbidity are known from scorpion stings from a few species, especially in the family Buthidae. Most of not all cases are caused by the toxic effect of the venom. Serious morbidity caused by allergic reactions to the venom is known from many venomous animals, but rarely reported in scorpions.

Iva Maria Lima Araújo Melo and co-workers have recently reported about a fatal case in Brazil where a man died after been stung by Jaguajir rochae (Borelli, 1910) Buthidae). This species was formerly in the genus Rhopalurus Thorell, 1876. Sting of Jaguajir/Rhopalurus have been considered mildly, and the few case reports that exist describe a mild course.

The present case had a very rapid course and the patient died before arriving to a hospital. All factors point to an allergic reactions as cause of death. The patient had a history of allergic reactions attributed to bee stings, and a cross reaction may explain why this patient develop such serious symptoms. Previously, a death from anaphylaxis due to a sting from Centruroides exilacauda has been reported from USA.

In conclusion, even though it is probably rare, sting from assumed harmless species may cause life-threatening allergic reactions. Especially in peoples with allergies.

Abstract:
A 44-year-old healthy farmer, was stung by a scorpion on his right hand while preparing soil for planting in the Caatinga area (a large area in the north-east of Brazil characterized by semiarid scrub forest), in the Catarina Municipality countryside, Ceará State, Brazil. According to the reports of carers and family members, the patient initially reported mild pain at the site of the sting, but within a few minutes he developed malaise, pruritus in the body and throat, edema in the nostrils, and a dry mouth which led to looking for water to drink. It rapidly evolved into sphincter, urinary and fecal release, salivation and a convulsive episode with loss of the senses. He was dead on arrival at Catarina Municipality Hospital emergency department. The necroscopic report indicated suffocation due to glottal edema and acute lung edema as the “cause of death”. The animal which caused the accident was under a rock that the patient was manipulating at the time of the incident, and has been identified by experts as Jaguajir rochae (Borelli, 1910) scorpion species, formerly synonymized Rhopalurus rochae. This is the first report of a fatality due to an allergic reaction to the venom of this species. This leads to the possibility that deaths caused by stings from other scorpion species may be due to anaphylaxis, whose symptoms in some situations may be confused with severe envenomation.

Reference: 
Melo IMLA, Ramalho RD, Bezerra MMV, de Oliveira Filho IE, Medeiros CR, da Costa Gadelha MA, et al. Fatal anaphylaxis to Jaguajir rochae (borelli, 1910) (Scorpiones, Buthidae) in Brazil: A case report. Journal of Tropical Pathology. 2019;48(3):1-8. [Open Access]

Jaguajir rochae is able to perceive differences between small and large prey and make decisions regarding venom usage

Several studies have shown that scorpions have different strategies for optimizing the venom use. The reason for this is of course because it take times to renew the venom and it is costly as the venom is a mixture of complex proteins. This is often called the venom optimization hypothesis. This also means that optimizing venom usage might directly affect the predatory behavior and physiology of scorpions.

Meykson Alexandre da Silva and co-workers have recently published an article showing that the amount of venom available for individuals of Jaguajir rochae (Borelli, 1910) (Butidae) did have an effect on their prey capture behavior. Individuals with depleted venom glands did not attack large prey, but did try to catch smaller prey that could be handled with pedipalps only. The study shows that this scorpion is able to perceive differences between small and large prey and make decisions regarding venom usage. These results are in accordance with the the venom optimization hypothesis

Abstract:
Animal venom is composed of a complex mixture of protein-rich chemicals. Synthesis of animal venom incurs a high metabolic cost and is a prolonged process; consequently, animals use their venom cautiously and economically. Some studies have shown that venomous animals modulate the amount and/or type of venom used depending on certain factors, such as prey size or the intensity of predation threat. Here, we investigated how the quantity of venom that is available for use by the scorpion Jaguajir rochae interferes with its choice of prey.We used two types of prey of contrasting size (small 200–300-mg and large 600–700-mg cockroaches). The results showed that the amount of venom influences the feeding behavior of this species. Most scorpions without venom exhibited a low interest when large prey was present, but frequently attacked small prey. The scorpions also showed a distinct pattern in the time between venom extraction and the initiation of hunting behavior. In conclusion, J. rochae is able to perceive differences between small and large prey and make decisions regarding venom usage, supporting the "venom optimization hypothesis" (or "venom metering hypothesis"), by minimizing the venom use due to it being an energetically expensive resource.

Reference:
Silva MA, Silvia NA, Lira AFA, Martins RD. Role of venom quantity in the feeding behavior of Jaguajir rochae (Scorpiones: Buthidae). Acta Ethologica. 2019;Published Online 09 March 2019. [Subscription required for full text]

Thanks to Meykson Alexandre da Silva for sending me their interesting article which confirm some of the assumptions that I did in my old studies of sting use in scorpions.

Environmental variation and seasonal changes as determinants of the spatial distribution of scorpion in Neotropical forests

Andre Lira and co-workers have recently published a new article on the population dynamics of scorpions in Neotropical forests. They found 12 species in the study area and collected data on microhabitat preferences, foraging activity, spatial distribution, seasonal changes effects etc.

Their main conclusion is that spatiotemporal resource partitioning and refuge sharing are important drivers of the population dynamics and spatial distribution of scorpion species in Neotropical forests. See abstract or article for more details.

Abstract:
Habitat selection and seasonal changes are key drivers of the population dynamics of many species. We analyzed how the environmental structure influences species establishment in an area by comparing microhabitat preference and functional richness of scorpions (Arachnida: Scorpiones) in wet (Atlantic forest) and semiarid (Caatinga) areas. Variations in superficial foraging activity and microhabitat colonization during dry and rainy seasons were evaluated as an indication of the climatic impact on population dynamics. We collected twelve scorpion species using ultraviolet light lamps. We found that differential patterns in spatial distribution were independent of forest type, and we provide evidence for partial niche partitioning among scorpion species based on age class and climatic conditions. Foraging activity was also seasonally influenced. Functional richness was higher in wet forests than in dry forests, whereas taxonomical richness exhibited an opposite pattern. We conclude that spatiotemporal resource partitioning and refuge sharing are important drivers of the population dynamics and spatial distribution of scorpion species in Neotropical forests.


Reference:
Lira A, DeSouza A, Albuquerque C. Environmental variation and seasonal changes as determinants of the spatial distribution of scorpion (Arachnida: Scorpiones) in Neotropical forests. Can J Zool. 2018;In Press. [Subscription required for full text]

Thanks to Andre Lira for sending me their article!

A systematic revision of the neotropical club-tailed scorpions, Physoctonus, Rhopalurus, and Troglorhopalurus has been published

Lauren Esposito and several co-workers have recently published a major systematic revision of the neotropical club-tailed scorpions, Physoctonus Mello-Leitao, 1934, Rhopalurus Thorell, 1876 and Troglorhopalurus Lourenço, Baptista & Giupponi, 2004 (Buthidae). This is a major study with many taxonomical changes. I have tried to sum up the main results here:

New genera:

Ischnotelson Esposito, Yamaguti, Souza, Pinto da Roacha & Prendini, 2017 (Brazil).

Jaguajir Esposito, Yamaguti, Souza, Pinto da Roacha & Prendini, 2017 (North and northeastern South America).

Heteroctenus Pocock, 1893 (revalidated from synonymization).

New species:

Ischnotelson peruassu Esposito, Yamaguti, Souza, Pinto da Roacha & Prendini, 2017 (Brazil).

Physoctonus striatus Esposito, Yamaguti, Souza, Pinto da Roacha & Prendini, 2017 (Brazil).

Rhopalurus ochoai Esposito, Yamaguti, Souza, Pinto da Roacha & Prendini, 2017 (Venezuela).

New combinations:

All of these species previously belonged to the genus Rhopalurus Thorell, 1876.

Heteroctenus abudi (Armas and Marcano Fondeur, 1987)

Heteroctenus bonettii (Armas, 1999)

Heteroctenus garridoi (Armas, 1974)

Heteroctenus gibarae (Teruel, 2006)

Heteroctenus princeps (Karsch, 1879)

Ischnotelson guanambiensis (Lenarducci et al., 2005)

Jaguajir agamemnon (C.L. Koch, 1839)

Jaguajir pintoi (Mello-Leitão, 1932)

Jaguajir rochae (Borelli, 1910)

Troglorhopalurus lacrau (Lourenço and Pinto-da-Rocha 1997)

Synonymizations:

"=" means "synonymized with".

Rhopalurus crassicauda Caporiacco, 1947 = Rhopalurus laticauda Thorell, 1876.

Rhopalurus amazonicus Lourenço, 1986 = Rhopalurus laticauda Thorell, 1876.

Rhopalurus crassicauda paruensis Lourenço, 2008 = Rhopalurus laticauda Thorell, 1876.

Rhopalurus brejo Lourenço, 2014 = Troglorhopalurus lacrau (Lourenço and Pinto-da-Rocha, 1997).

Rhopalurus acromelas Lutz and Mello, 1922 = Jaguajir agamemnon (C.L. Koch, 1839).

Rhopalurus melleipalpus Lutz and Mello, 1922 = Jaguajir agamemnon (C.L. Koch, 1839).

Rhopalurus iglesiasi Werner, 1927 = Jaguajir agamemnon (C.L. Koch, 1839).

Rhopalurus lambdophorus Mello-Leitão, 1932 = Jaguajir agamemnon (C.L. Koch, 1839).

Rhopalurus dorsomaculatus Prado, 1938 = Jaguajir agamemnon (C.L. Koch, 1839).

Rhopalurus goiasensis Prado, 1940 = Jaguajir agamemnon (C.L. Koch, 1839).

Rhopalurus aridicola Teruel and Armas, 2012 = Heteroctenus junceus (Herbst, 1800).

Rhopalurus melloleitaoi Teruel and Armas, 2006 = Heteroctenus junceus (Herbst, 1800).

Rhopalurus granulimanus Teruel, 2006 = Heteroctenus gibarae (Teruel, 2006).

Rhopalurus virkkii Santiago-Blay, 2009 = Heteroctenus abudi (Armas and Marcano Fondeur, 1987).

The article has an updated identification key for the involved taxa.

Abstract:

Reference:
Esposito LA, Yamaguti HY, Souza CA, Pinto da Rocha R, Prendini L. Systematic revision of the neotropical club-tailed scorpions, Physoctonus, Rhopalurus, and Troglorhopalurus, revalidation of Heteroctenus, and descriptions of two new genera and three new species (Buthidae: Rhopalurusinae). Bulletin of the American Museum of Natural History. 2017(415):1-134. [Open Access]

Thanks to Ricardo Pinto-da-Rocha and Carlos Turiel for sending me this article!

Family Buthidae