Phylogenetic study gives Hadruridae family status ("Another one bites the dust")

There have been buzz about Carlos E. Santibáñez-López' and co-worker's new phylogenetic study of the family Caraboctonidae Kraepelin, 1905 for several months, but due to several reasons I have been slow to post this on the blog. But here it is and The Scorpion Files' family pages have also been updated.

I'm not going to go into details about the study here as I must admit that the more technical stuff is above my head, but I will list the main conclusions from the study:

1.
Hadrurinae Stahnke, 1973 is split from Caraboctonidae and elevated to family status, Hadruridae. Hadruridae consists of nine species in the two genera Hadrurus Thorell, 1876 and Hoffmannihadrurus Fet & Soleglad, 2004. Distributed in North America.

2.
Caraboctonidae now consists of 23 species in two two genera Caraboctonus Pocock, 1893 and Hadruroides Pocock, 1893. Distributed in South America.

3.
Two new superfamilies have been created: Caraboctonoidea Kraepelin, 1905 (Caraboctonidae and Superstitioniidae) and Hadruroidea Stahnke, 1974 (Hadruridae).

4.
The genera Uroctonus Thorell, 1876  (currently in Chactidae)  and Belisarius Simon, 1879 (currently in Belisaridae) are regarded as insertae sedis with respect to superfamilial placement.

More phylogenomic analyses will probably give us more insight in the complicated higher-level relationships in scorpions.

Abstract:
Historically, morphological characters have been used to support the monophyly, composition, and phylogenetic relationships of scorpion families. Although recent phylogenomic analyses have recovered most of these traditional higher level relationships as non-monophyletic, certain key taxa have yet to be sampled using a phylogenomic approach. Salient among these is the monotypic genus Caraboctonus Pocock, 1893, the type species of the family Caraboctonidae Kraepelin, 1905. Here, we examined the putative monophyly and phylogenetic placement of this family, sampling the library of C. keyserlingi Pocock, 1893 using high throughput transcriptomic sequencing. Our phylogenomic analyses recovered Caraboctonidae as polyphyletic due to the distant placement of the genera Caraboctonus and Hadrurus Thorell, 1876. Caraboctonus was stably recovered as the sister-group of the monotypic family Superstitioniidae Stahnke, 1940, whereas Hadrurus formed an unstable relationship with Uroctonus Thorell, 1876 and Belisarius Simon, 1879. Fourcluster likelihood mapping revealed that the instability inherent to the placement of Hadrurus, Uroctonus and Belisarius was attributable to significant gene tree conflict in the internodes corresponding to their divergences. To redress the polyphyly of Caraboctonidae, the following systematic actions have been taken: (1) the family Caraboctonidae has been delimited to consist of 23 species in the genera Caraboctonus and Hadruroides Pocock, 1893; (2) Caraboctonidae, previously included in the superfamily Iuroidea Thorell, 1876 or as incertae sedis, is transferred to the superfamily Caraboctonoidea (new rank); (3) the superfamily Hadruroidea (new rank) is established and the status of Hadrurinae Stahnke, 1973 is elevated to family (Hadruridae new status) including 9 species in the genera Hadrurus and Hoffmannihadrurus Fet & Soleglad, 2004 and (4) we treat Uroctonus and Belisarius as insertae sedis with respect to superfamilial placement. Our systematic actions engender the monophyly of both Iuroidea and Caraboctonidae. Future phylogenomic investigations should target similar taxon-poor and understudied

References:
Santibáñez-López CE, Ojanguren-Affilastro AA, Sharma PP. Another one bites the dust: Taxonomic sampling of a key genus in phylogenomic datasets reveals more non-monophyletic groups in traditional scorpion classification. Invertebrate Systematics. 2020;34(2):133-43. [Subscription required for full text]

Thanks to Carlos E. Santibáñez-López and Prashant P. Sharma who have kept me informed about their study. I have also been informed about this article by Kari McWest and Matt Simon. Big thanks to them!

Family Caraboctonidae
Family Hadruridae

Scorpions can actually smell their enemies

It has been known for a long time that scorpions can smell (detect chemical substances) with their pectines and pedipalpal fingers. Zia Nisani and Raul Curiel report for the first time that scorpions are also able to smell the presence of potential predators. In a research trial they were able to show that individuals of Hadrurus arizonensis (Ewing, 1928) (Caraboctonidae) changed behavior in the presence of odor from a potential predator. The advantages of such an ability is of course quite obvious.

Abstract:
Sensory ecology studies show that reception and utilization of information from the environment is a crucial life process. Scorpions possess a weapon that can be used against predators, but it remains unknown whether scorpions’ decision to use it is influenced by chemical cues from predators. We investigated the influence of predators’ odors on stinging behavior of Hadrurus arizonensis (Ewing, 1928) by stimulating them to sting under two conditions: in the presence of an odor from a potential rodent predator (Rattus norvegicus) and in the absence of such an odor. It took fewer probes to elicit a response when predator scent was present, and it resulted in more wet stings than the non-scented treatments. Finally, the smaller scorpions were more reactive than the larger ones. The variances in stinging behavior suggest that the detection of predator odors by H. arizonensis elevates its response in potentially threatening circumstances.

Reference:
Nisani Z, Curiel R. Antipredator responses of Hadrurus arizonensis (Scorpiones: Caraboctonidae) to chemosensory cue from a mammalian predator. J Arachnol. 2019;47:389-91. [Open Access]

The defense respons of scorpions to repeated attacks from a predator

Scorpions and other prey species are involved in a continuing arm race against their predators. The prey will get better in avoidance and defence and the predator tries to get better in overcoming the prey.

Mykola Rasko and co-workers have recently published a study investigating the sting use and venom expenditure during repeated attacks (simulated) in Hadurus arizonensis Ewin, 1928 (Caraboctonidae). Contrary to the projects expectations, the stinging behaviour, venom use and venom volume all decreased as the number of challenges increased. The scorpions defenses actually decreased during repeated attacks. This means that a predator of scorpions should use repeated attacks to overcome a scorpion, and this is also something that has been observed in some predators of scorpions.

Abstract:
Predatore-prey arms races ensure that a prey's defences are well matched with the predator's ability to overcome them. Scorpions have a formidable defensive capacity due to their venomous stinger. Mammalian and squamate scorpion predators overpower scorpions by making repeated attacks. We tested here how scorpions, Hadrurus arizonensis, apply their venom defensively during a simulated repeated attack, consisting of 10 consecutive challenges. Since the persistent repeated attack of a predator, even when stung in the process, seems to indicate its resolve, we expected defensive effort to increase with the number of challenges. We also expected that, owing to the life-and-death nature of a predatory attack, scorpions would be liberal in the use of their venom. We found, however, that stinging behaviour, venom use and venom volume all decreased as the number of challenges increased. Scorpions used only 7.8±9.6% (mean±SD) of their total venom volume during an attack consisting of 10 consecutive challenges. We conclude that a repeated attack seems an effective strategy for scorpion predators to reduce the defensive investment of scorpions.

Reference:
Rasko M, Coelho P, Simone Y, van der Meijden A. How to attack a scorpion: venom metering during a repeated attack. Anim Behav. 2018;145:125-9. [Subscription required for full text]

A desert scorpion can smell its enemies

Avoid being eaten or killed is one of the fundamental drives in all animals and an impressive range of anti-predator tactics have been described. Scorpions have their powerful claws and a venomous sting, but other tools are also available.

Zia Nisani and co-workers have now published a very interesting article showing that the desert scorpion Paruroctonus marksi (Haradon, 1984) (Vaejovidae) can actually smell the proximity of a potential predator (in this case the much larger scorpion Hadrurus arizonensis (Ewing, 1928) (Caraboctonidae)) and then avoid approaching it. This is the first evidence of airborne chemoreception as an anti-predator strategy in scorpions.

One of the experiments in this study point to a special constellation array of sensilla (or a yet unidentified structure) on the pedipalps as the "sense organ" used to detect the odors of predators.

Abstract:
Chemically induced predator avoidance behaviors exist in many arthropods. In this paper, we examined the behavioral responses of the desert scorpion, Paruroctonus marksi (Haradon, 1984), to airborne chemical cues from a natural predator, the larger scorpion Hadrurus arizonensis (Ewing, 1928). We used a Y-shaped, dual-choice olfactometer to test for avoidance behavior in the presence of a known predator, H. arizonensis. Prior to this study there has been little research done on chemically induced predator avoidance behaviors in scorpions. The results of this study suggest that P. marksi is capable of detecting a predator’s airborne cues, though the nature and identity of these cues remain unknown, and it appears that the constellation array of the fixed finger does function in detecting these cues. We also discuss the importance of adaptive predator avoidance behaviors.

Reference:
Nisani Z, Honaker A, Jenne V, Loya F, Moon H. Evidence of airborne chemoreception in the scorpion Paruroctonus marksi (Scorpiones: Vaejovidae). Journal of Arachnology. 2018;46:40-4. [Open Access]

Thanks to Matt Simon for informing me about this article!

Phylogeography of the Arizona Hairy Scorpion (Hadrurus arizonensis)

Matthew Graham and co-workers have recently published an interesting and extensive article on the phylogeography of the Arizona Hairy Scorpion (Hadrurus arizonensis Ewing, 1928 - family Caraboctonidae). Phylogeography is the study of the historical processes that may be responsible for the contemporary geographic distributions of individuals (Wikipedia).

The authors conclude that mitochondrial sequence data suggest that the phylogeography of H. arizonensis was shaped by a history of fragmentation, reduced gene flow and demographic expansion since the late Pliocene. See abstract below for more details.

Abstract:
Aim As data accumulate, a multi-taxon biogeographical synthesis of the Mojave Desert is beginning to emerge. The initial synthesis, which we call the ‘Mojave Assembly Model’, was predominantly based on comparisons of phylogeographical patterns from vertebrate taxa. We tested the predictions of this model by examining the phylogeographical history of Hadrurus arizonensis, a large scorpion from the Mojave and Sonoran deserts.
Location Mojave and Sonoran deserts, United States and Mexico.
Methods We sequenced mitochondrial cytochrome c oxidase subunit I (COI) data from 256 samples collected throughout the range of H. arizonensis. We analysed sequence data using a network analysis, spatial analysis of molecular variance (SAMOVA), and a Mantel test. We then used a molecular clock to place the genetic patterns in a temporal framework. We tested for signals of expansion using neutrality tests, mismatch distributions and Bayesian skyline plots. We used Maxent to develop current and late-glacial species distribution models from occurrence records and bioclimatic variables.
Results Phylogenetic and structure analyses split the maternal genealogy basally into a southern clade along the coast of Sonora and a northern clade that includes six lineages distributed in the Mojave Desert and northern Sonoran Desert. Molecular dating suggested that the main clades diverged between the late Pliocene and early Pleistocene, whereas subsequent divergences between lineages occurred in the middle and late Pleistocene. Species distribution models predicted that the distribution of suitable climate was reduced and fragmented during the Last Glacial Maximum.
Main conclusions Genetic analyses and species distribution modelling suggest that the genetic diversity within H. arizonensis was predominantly structured by Pleistocene climate cycles. These results are generally consistent with the predictions of Pleistocene refugia for arid-adapted taxa described in the Mojave Assembly Model, but suggest that a northern area of the Lower Colorado River Valley may have acted as an additional refugium during Pleistocene glacial cycles.

Reference:
Graham MR, Jaeger JR, Prendini L, Riddle BR. Phylogeography of the Arizona hairy scorpion (Hadrurus arizonensis) supports a model of biotic assembly in the Mojave Desert and adds a new Pleistocene refugium. Journal of Biogeography. 2013. Epub 30 Jan 2013. [Full text required for full text]

Thanks to Matthew Graham for sending me his paper!

Density, spatial distribution and biomass of Hoffmannihadrurus gertschi

Ana Quijano-Ravell and co-workers have recently published an article on the density, spatial distribution and biomass of Hoffmannihadrurus gertschi (Soleglad, 1976) (Caraboctonidae)* in an area in Mexico.

The paper is written in Spanish so I have only read the English abstract.

[*The authors have placed this species in Hadrurus, but it was transfered to Hoffmannihadrurus by Fet & Soleglad i 2008 and this species is listed as Hoffmannihadrurus gertschi (Soleglad, 1976) in The Scorpion Files. Some scientists disagree on the validity of Hoffmannihadurus, as this paper is an example of. Also, some scientists choose to put Hadrurus in Iuridae and reject the validity of Caraboctonidae. See details here.]

Abstract:
Density, spatial dispersion and biomass of Hadrurus gertschi Soleglad 1976 were estimated from field data obtained during a year of observations at “La Coronilla” hill in the municipality of Tepecoacuilco de Trujano, Guerrero, Mexico. Five quadrants of 400 m2 with differing slope exposures were used. The highest density was recorded in the quadrant without slope or “flat quadrant” with 0.3450 burrows per m2 and the southern exposure quadrant (0.2300 burrows per m2). The lowest densities occurred in the quadrants with northern and western exposures (0.1325 and 0.0825 burrows per m2 respectively). The highest values of the year were recorded in the months of May to July. The spatial dispersion of burrows in all exposures studied corresponds with a clumped distribution according to the Morisita Index. Average dry weight of adults was 2.22 ± 0.73 g and 6.4 ± 0.89 g in fresh weight. The juveniles weighted 0.08 ± 0.05 g in dry weight and 0.2 of fresh weight instar II and 1.10 ± 0.41 g dry weight and 3.63 ±1.95 g in fresh weight in the preadult stage. The biomass per ha was estimated in 2471.26 g of dry weight and 6190.02 g of fresh weight.

Reference:
Quijano-Ravell AF, Ponce-Saavedra J, Francke OF. Densidad, distribucion espacial y biomasa de Hadrurus gertschi Soleglad (Scorpiones, Iuridae) en una localidad de Guerro, Mexico. Revista Iberica de Arachnologia. 2012;20:35-43.

Thanks to Dr. Francke for sending me this paper!

Family Caraboctonidae

Burrows and burrowing in Hadrurus arizonensis

Daniel Hembree and co-workers have recently published a paper describing the forms and shapes of Hadrurus arizonensis Ewing, 1928 (Caraboctonidae) burrows. The authors are geologists (and/or palaentologists), and the angle and terminology of this papers is somewhat different from what I'm used to from the traditional scorpion literature. I must admit there are quite a few terms in the paper that unknown to me (but praise Google for being a helpful friend ;)

The goal of the paper is both to learn more about scorpion burrows, but also to aid in the recognition of scorpion burrows in the fossil record and to determine if aspects of palaeoenvironment can be ascertained by variations in scorpion burrow morphology.

The paper also has a nice mini-review of scorpion burrowing behavior and several pictures of burrow castings showing the form and shape of Hadrurus burrows.

Abstract:
Bioturbation by terrestrial animals is common in arid and semi-arid continental environments. Scorpions have comprised a significant portion of the diversity of predatory arthropods in these environments from the Late Paleozoic to the Recent. Many scorpions are active burrowers and likely have a substantial, if rarely recognized, ichnofossil record. This project involved the study of the burrowing behaviors and trace morphologies of the scorpion Hadrurus arizonensis (Scorpiones: Caraboctonidae). Individual animals were placed into sediment-filled terrariums for two- to three-week periods after which burrows were cast, excavated, and described. Descriptions of the subsurface structures included architecture, dimensions, bioglyphs, complexity, and tortuosity. Additional experiments were run with differing sediment composition, density, and moisture to evaluate the animal’s behavioral response to altering environmental conditions. Specimens of H. arizonensis burrowed by scratching and kicking loose sediment from the subsurface with the first two to three pairs of walking legs. The subsurface biogenic structures produced consisted of subvertical ramps, U-shaped burrows, helical burrows, and mazeworks. In the process of excavating the burrows, the desert scorpions also produced a hummocky surface topography as well as structures in dry, sandy sediment that resembled lamination and ripple cross-lamination. Increasing clay content and sediment density increased the complexity of burrow architectures produced. Reducing these variables limited the complexity of the burrows, reduced their likelihood of preservation, and increased the abundance of biogenic cross-lamination. Data collected from these and similar experimental studies can be applied to terrestrial ichnofossil assemblages in order to better interpret the paleoecology of ancient soil ecosystems.

Reference:
Hembree DI, Johnson LM, Tenwalde RW. Neoichnology of the desert scorpion Hadrurus arizonensis: burrows to biogenic cross lamination. Palaeontologia Electronica. 2012;15(1):1-34. [ Free full text]

Thanks to Jahn Hornung for informing me about this paper!

Life cycle of Hadrurus gertschi from Mexico

Ana Quijano-Ravell and co-workers have now published a study on the life cycle of Hadrurus gertschi Soleglad, 1976 (Caraboctonidae)*

[*This species was transfered to Hoffmannihadrurus by Fet & Soleglad i 2008 and this species is listed as Hoffmannihadrurus gertschi (Soleglad, 1976) in The Scorpion Files. Some scientists disagree on the validity of Hoffmannihadurus, as this paper is an example of. Also, some scientists choose to put Hadrurus in Iuridae and reject the validity of Caraboctonidae. See details here.]

Abstract:
The life cycle of Hadrurus gertschi Soleglad 1976 was reconstructed from field data taken during one year of observations in “La Coronilla”, near Ahuehuepan, in Tepecoacuilco de Trujano municipality, Guerrero, Mexico. The species inhabits tropical dry schrub forest in sympatry with three other scorpion species: Centruroides limpidus (Karsch 1879), Vaejovis variegatus Pocock 1898 and Vaejovis atenango Francke and González-Santillán 2007. A growth factor of 1.27 for the carapace length was determined and then used to estimate the morphometric changes between each instar to reach the adult stage and compared them with data obtained in the field. We concluded that this species requires 7 instars and 6 molts, and at least four years to reach adulthood. We also present the phenology of Hadrurus gertschi during one year, measured in relative abundance and surface activity pattern. Matting activity was observed in July, August, September and October.

Reference:
Quijano-Ravell AF, Ponce-Saavedra J, Francke OF. Ciclo de vida de Hadrurus gertschi Soleglad (Scorpiones, Iuridae) en una localidad del Estado de Guerrero, Mexico. Revista Iberica de Arachnologia. 2011;19(133-145).

Thanks to Oscar Francke for sending me this paper!

Family Caraboctonidae

More on the genera Hadrurus and Hoffmannihadrurus

Michael Soleglad and Victor Fet have recently published a paper with further observations on the genera Hadrurus Thorell, 1876 and Hoffmannihadrurus Fet & Soleglad, 2004 (both Caraboctonidae).

Abstract:
Multiple populations of Hadrurus pinteri from Baja California Sur, Mexico have been examined. It is demonstrated that the southern populations of this species have a larger number of accessory trichobothria (neobothriotaxy) than the northern populations, numbers exceeding the maximum currently recorded for the genus. Examination of carapace and chela coloration and its patterns show a close affinity between H. pinteri and the dark phase of H. concolorous. A new morphometric ratio of the carapace is defined that distinguishes Hadrurus from Hoffmannihadrurus, further supporting the monophyly of the latter genus.

Reference:
Soleglad ME, Fet V. Further observations on scorpion genera Hadrurus and Hoffmannihadrurus (Scorpiones, Caraboctonidae). ZooKeys. 2010;59:1-13. [Free fultext]

Thanks to Victor Fet for sending me this paper!

Family Caraboctonidae

Sting use in prey capture

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.

Now, Martin Edmunds and Richard Sibly have published a similar study with similar conclusions, using Hadrurus spadix Stahnke, 1940 (Caraboctonicae).

Abstract:
Since venom is costly to produce and stinging is not obligatory in prey capture for scorpions, the need to optimize use of resources suggests that venom should be reserved for prey that cannot otherwise be overpowered, (i.e., larger and/or more active prey). In accordance with these predictions, sting use by Hadrurus spadix Stahnke 1940 increased with prey size, reaching 100% once prey items were longer than the scorpion’s pedipalp patella length, and with prey activity, which we manipulated by varying prey temperature. Surprisingly, the scorpions were slower to capture less active (cooler) prey than those that exhibited higher rates of activity. We suggest this is because prey are located by vibrations in the substrate, with less active prey producing fewer vibrations.

Reference:
Edmunds MC, Sibly RM. Optimal sting use in the feeding behavior of the scorpion Hadrurus spadix. Journal of Arachnology. 2010;38(1):123-5. [Subscription required for fulltext, but free fulltext after 12 months].

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

Cladistic analysis of superfamily Iuroidea, with emphasis on subfamily Hadrurinae (Scorpiones: Iurida) and Hoffmannihadurus is reinstated

The Caraboctonid genus Hoffmannihadrurus Fet & Soleglad, 2004 was synonized with Hadrurus by Francke & Prendini, 2008 in June in their review of the taxonomic history of the North American genus Hadrurus.

This decision has now been refuted by Fet & Soleglad, 2008 in their recently published cladistic analysis of superfamily Iuroidea, with emphasis on subfamily Hadrurinae. The genus Hoffmannihadrurus is reinstated and the two species belonging to the genus are transfered from Hadrurus:

Hoffmannihadrurus Fet & Soleglad, 2004 (Caraboctonidae)

Hoffmannihadrurus aztecus (Pocock, 1902)
Hoffmannihadrurus gertschi (Soleglad, 1976)

References:
Fet V, Soleglad ME. Cladistic analysis of superfamily Iuroidea, with emphasis on subfamily Hadrurinae (Scorpiones: Iurida). Boletin Sociedad Entomológica Aragonesa. 2008(43):255-81.

Family Caraboctonidae

A phylogenetic review of the genus Hadurus and synonymization of Hoffmannihadrurus with Hadurus

Oscar Francke and Lorenzo Prendini have recently published a paper where they review the taxonomic history of the North American genus Hadrurus Thorell, 1876 and re-evaluate the phylogenetic relationships among the genus' species. In the same paper they also propose a synonymization of Hoffmannihadrurus Fet & Soleglad 2004 with Hadrurus. This means that the following names are valid for the two species previously included in Hoffmannihadrurus:

Hadrurus aztecus Pocock, 1902
Hadrurus gertschi Soleglad, 1976

Here is the abstract of the paper:

The ‘giant hairy scorpions’, genus Hadrurus Thorell, are the largest and most conspicuous scorpions in North America, but their systematics has long been confused. A new genus, Hoffmannihadrurus Fet et al. was recently created to accommodate the two species endemic to mainland Mexico, Hadrurus aztecus Pocock and Hadrurus gertschi Soleglad. In the present contribution, we review the taxonomic history of Hadrurus, re-evaluate the phylogenetic relationships among its component species with an analysis based on morphological characters and a taxon sample representing the known morphological variation, and assess the validity of the new genus. Seven independent analyses of the morphological character matrix, under weighting regimes that minimised length as well as those that maximised fit, each located a single most parsimonious tree with the following scheme of relationships: (Iurus ((Caraboctonus + Hadruroides) (H. aztecus ((H. gertschi + H. pinteri) (H. concolorous + H. hirsutus)) ((H. obscurus + H. spadix) (H. a. arizonensis (H. a. austrinus + H. a. pallidus)))))). This topology supports the monophyly of Caraboctoninae, Caraboctonini, Hadrurini, the ‘arizonensis’ subgroup, H. arizonensis and H. concolorous. It does not support the monophyly of Hoffmannihadrurus, Hadrurus, the ‘aztecus’ group, the ‘hirsutus’ group, and the ‘hirsutus’ subgroup, all of which were rendered paraphyletic by the grouping of H. gertschi with H. pinteri, rather than with H. aztecus. The results unequivocally demonstrate that the creation of a new genus for the mainland Mexican species was unfounded. We therefore propose the following new synonymy: Hoffmannihadrurus Fet et al., 2004 = Hadrurus Thorell, 1876, syn. nov.

Did you know that in Mexico the large Hadrurus are known as "Matacaballos", which actually means "Horse killers". Fortunately, studies have shown that the venom of these impressing scorpions has low toxicity against mammals.

Reference:
Francke OF, Prendini L. Phylogeny and classification of the gigant hairy scorpions, Hadrurus Thorell (Iuridae Thorell): a reappraisal. Systematics and Biodiversity. 2008;6(2):205-23. [Subscription required for fulltext]

Family Caraboctonidae