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Accepted Manuscript

Dangerous —Fake news or reality?

Tobias J. Hauke, Volker Herzig

PII: S0041-0101(17)30269-6 DOI: 10.1016/j.toxicon.2017.08.024 Reference: TOXCON 5708

To appear in: Toxicon

Received Date: 22 June 2017 Revised Date: 28 July 2017 Accepted Date: 27 August 2017

Please cite this article as: Hauke, T.J., Herzig, V., Dangerous arachnids—Fake news or reality?, Toxicon (2017), doi: 10.1016/j.toxicon.2017.08.024.

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT

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Highlights

• The increasing popularity of arachnids as pets urges some governments to take protective action to prevent serious envenomations • A literature review was carried out to assess which arachnids can be classified as potentially dangerous • About 0.5% of all and 23% of all were classified as potentially dangerous • Even envenomations from the most dangerous arachnids have a low percentage of serious or even fatal consequences • We conclude that the public threat from pet envenomations has been overrated

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1 ACCEPTED MANUSCRIPT Review Dangerous arachnids—fake news or reality?

Tobias J. Hauke 1, Volker Herzig 2

1 Department of Pharmacy – Center of Drug Research, Ludwig ‐Maximilians ‐Universität München, 81377 Munich, 2 Institute for Molecular Bioscience, The University of , St. Lucia QLD 4072,

Running head: Medically important arachnids

*Address correspondence to: Volker Herzig, Institute for Molecular Bioscience, The University of Queensland, St. Lucia QLD 4072, Australia; Phone: +61 7 3346 2018, Fax: +61 7 3346 2101, Email: [email protected] MANUSCRIPT

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2 ACCEPTED MANUSCRIPT Abstract The public perception of and is skewed towards the potential harm they can inflict in , despite recent scientific evidence that arachnid components might be useful as bioinsecticides or even therapeutics. Nevertheless, arachnids are becoming more popular as pets in , America and , raising the question for regulatory agencies in these regions as to whether they need to take measurements to protect their citizens. In order to decide upon the necessary regulatory steps, they first need to determine which arachnids are actually dangerous to humans. This review therefore provides an overview of the current literature on verified bites and stings from spiders and scorpions with the aim of assessing their potential danger for human health. As a guideline, we also provide a list of those arachnid genera that we consider as potentially dangerous, which includes 10 spider and 11 scorpion genera. The arachnid genera classified as dangerous comprise less than a quarter of all extant scorpion species and only 0.5% of all spiders species, with the actual number most likely being much lower than that, as not all species in those genera might turn out to pose an actual threat for humans. In conclusion, we found that only a small percentage of scorpions and a minute percentage of all spiders can be considered as potentially dangerous to humans. While in some countries of origin the high incidence of envenomations by dangerous arachnids can resultMANUSCRIPT in a serious problem to the health system, we assessed the risk that the same species pose when kept as pets under controlled maintenance conditions as significantly lower.

Keywords arachnid, spider,ACCEPTED scorpion, pet, venom, , lethal, envenomation, bite, sting

3 ACCEPTED MANUSCRIPT 1. Introduction The general public usually perceives spiders and scorpions as aggressive, dangerous and lethal (Stuber and Nentwig, 2016), a view that is constantly reinforced by Hollywood movies. However, in recent years, other media outlets also published reports about the positive potential of arachnid venom peptides that are being developed as bioinsecticides (Windley et al., 2012; King and Hardy, 2013) or as potential therapeutics for human disorders such as pain, atrial fibrillation, erectile dysfunction, irritable bowel syndrome, stroke, and bacterial, fungal or protozoan infections (Saez et al., 2010; Smith et al., 2013; Osteen et al., 2016; Chassagnon et al., 2017). Furthermore, with a growing worldwide pet trade, keeping exotic "pet" spiders or scorpions is becoming an increasingly popular hobby in Europe, America and Asia. Thus, a question that arises for regulatory authorities in various countries is whether they need to take action to protect their citizens from potentially dangerous arachnids. However, authorities first need to determine which species are actually potentially dangerous to human health. Unfortunately, based on our experience with German authorities (Hauke et al., 2015), this information is often obtained from older scientific literature or textbooks or even from non-scientific sources (e.g. Internet). Hence, this review provides an update on the scientific literature on venomous arachnids focussing on those species that could potentially harm humans and it could therefore serve as a guideMANUSCRIPTline for regulatory agencies.

Although arachnids comprise other venomous orders such as Pseudoscorpiones (von Reumont et al., 2014) and recently also certain were suggested to be considered as venomous (Cabezas-Cruz and Valdes, 2014) we focussed this review on spiders (order Araneae) and scorpions (Scorpiones) as they are the primary arachnids kept as exotic pets. In order to determine which arachnids might be dangerous, we mainly investigated more recent scientific literature. In older literature, the taxonomic identification is often missing, unclear, some species could have been misidentified or single species could later be split up into several new species. This makes it difficult in retrospect to determine the actual species responsible for ACCEPTED any reported adverse effects. We therefore preferably used (if available) articles studying verified (definite, confirmed) rather than presumed bites and stings based on the criteria defined by Isbister and White (2004). Ideally, correct taxonomic identification should be carried out by an expert taxonomist. The reason why proper identification is essential is exemplified in the case of bites by spiders of the Loxosceles , which were blamed for necrotic effects in geographical areas where they don't even exist (Vetter, 2005). Furthermore, a recent study examining 134 medical case studies found that only 22% fulfilled

4 ACCEPTED MANUSCRIPT the criteria for a verified , questioning the scientific value of many studies in this field (Stuber and Nentwig, 2016). Finally, studies examining large numbers of bites and stings were preferred to single case reports, as they allow for statistical analysis and an estimation of the incidence of various envenomation symptoms. Good examples of these larger studies include the prospective study of 750 definite bites by Australian spiders (Isbister and Gray, 2002) and the Brazilian clinico-epidemiological studies on 422 bites by spiders (Bucaretchi et al., 2000) and 1327 stings by scorpions (Bucaretchi et al., 2014). Overall, recent clinical studies provide a clear picture that only a very small percentage of arachnid bites or stings cause serious adverse or even lethal effects (Welton et al., 2017). However, the high incidence of accidental envenomations by certain arachnids still causes a massive problem for the health system in some countries (Chippaux and Goyffon, 2008). In addition to clinical studies, recent technical advances in the fields of biochemistry and molecular biology have rapidly increased our knowledge about the composition of arachnid , leading to a clearer understanding of the mode of action of and other venom components (Kuhn-Nentwig et al., 2011; Quintero-Hernandez et al., 2013). These studies have provided a better molecular-level understanding of the activity of venoms, enabling a judgement whether a proposed clinical symptom might be explained by any of the components contained in the venom. MANUSCRIPT

Based on evidence in the scientific literature, the public perception of venomous arachnids is biased towards their negative effects. With the present review, we aim to provide a more objective evidence-based assessment of the danger that arachnids pose for human health. We therefore first provide an overview of all arachnids that are considered medically important, before discussing those species with questionable potential to cause human harm. We then assess the potential danger of arachnids for human health before proposing a list of arachnid genera that we consider as potentially dangerous to humans.

2. Potentially dangerousACCEPTED arachnids Herein we consider “potentially dangerous” arachnids as those whose bite or sting was demonstrated (i.e. in primary literature) to cause severe (i.e. systemic and/or long-lasting) envenomation symptoms or even death. Although all scorpions (about 2,300 described species) and about 99% of all spiders (~47,000 described species) need to be considered “venomous” (all known spiders with the exception of those in the possess venom glands (Foelix, 2011)), only few them pose a threat to humans. Their venom has

5 ACCEPTED MANUSCRIPT evolved primarily to immobilize potential prey (typically such as (Windley et al., 2012)), although some venom components might also be used for defensive purposes (Inceoglu et al., 2003; Siemens et al., 2006; Osteen et al., 2016). The potentially dangerous arachnid families/genera are listed below in alphabetical order.

2.1 Spiders (order Araneae): 2.1.1 Genus (family ; Fig. 1): Bites by mouse spiders ( Missulena spp.) are typically considered harmless and mostly result in only mild symptoms (Herzig et al., 2008). However, according to one case report, a child aged 19-months developed severe systemic symptoms including hypertension, muscle spasms and unconsciousness after being bitten by . The symptoms were treated with originally developed against Atrax and Hadronyche bites (Isbister, 2004a). Toxinological studies revealed that Missulena venom contains components with high similarity to the lethal δ- hexatoxins found in the venom of Australian funnel-web spiders (Gunning et al., 2003; Herzig et al., 2011). Recently, a close phylogenetic relationship between Missulena , Atrax and Hadronyche was demonstrated (Hedin and Bond, 2006; Bond et al., 2012). Due to these toxinological and phylogenetic findings, we regard it as highly likely that the severe systemic symptoms described by Isbister (2004a) were a direcMANUSCRIPTt consequence of envenomation and not caused by other circumstances. Thus, we consider spiders of the genus Missulena as potentially dangerous although there is just one verified bite with severe manifestations reported from literature.

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Figure 1. Potentially dangerous Actinopodidae: Missulena spec . (Photograph by Michael Gray).

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2.1.2 Genus Phoneutria (family Ctenidae; Fig. 2): Phoneutria species are distributed in Central and and are considered of medical relevance (Isbister and Fan, 2011). Most bites are reported from . Bite symptoms can be classified as mild (~90% of all cases), moderate (8.5%) or severe (0.5%), while about 1% of the patients do not show signs of envenomation. In severe envenomations, patients developed acute pulmonary oedema with one fatal outcome described. However, severe envenomations were restricted to small children of the age of nine months and three years, respectively (Bucaretchi et al., 2000). Several peptidic toxins were isolated from Phoneutria venoms that act on ion channels (Gomez et al., 2002), which might be responsible for the neurotoxic envenomation symptoms.

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Figure 2. Potentially dangerous Ctenidae: Phoneutria nigriventer (Photograph by Bastian Rast).

2.1.3 Genera Atrax, Hadronyche, and Illawarra (family ; Fig. 3): Australian funnel-web spiders are considered medically important for humans in south-eastern Australia. The symptoms after bites include local effects such as severe pain, fang marks/bleeding and redness, regional effects like paraesthesia, fasciculations or diaphoresis, and severe systemic effects such as autonomic or cardiovascular effects and pulmonary oedema. Severe systemic effects occur in about 13% of all bites and are considered typical for funnel-web spider envenoming in ACCEPTED comparison with other mygalomorph spiders (Isbister and Gray, 2004b). However, no fatalities from funnel-web spider bites have been recorded since the 1980s, which is attributed to the development of an effective antivenom (Hartman and Sutherland, 1984; Isbister et al., 2005). The dangerous funnel-web spiders belong to the hexathelid subfamily Atracinae, which comprises the genera Atrax , Hadronyche and Illawarra . Most incidents are caused by male Sydney funnel-web Atrax robustus , but incidents with severe

7 ACCEPTED MANUSCRIPT envenoming are also frequently reported from Hadronyche cerberea and H. formidabilis (Isbister et al., 2005). Toxinological studies imply that the venom components responsible for the symptoms in humans (i.e. the so-called δ-hexatoxins that act on voltage-gated sodium channels), initially isolated and characterized from Atrax and Hadronyche venoms, are also present in the venoms of Illawarra species (Herzig et al., 2011). Thus, we expect similar effects from bites by Illawarra as reported for Atrax and Hadronyche bites. As the genus Illawarra was only established in 2010 (Gray, 2010), this might explain why no bite reports have yet been published.

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Figure 3. Potentially dangerous Hexathelidae: (A) Atrax robustus , ( B) (Photographs by Volker Herzig ( A) & Bastian Rast ( B)).

2.1.4 Genera , Loxosceles, and (family ; Fig. 4): A comprehensive study examined the necrotizing potential of venoms from 45 spider species in 20 different families (Foradori et al., 2005). It was found that only venoms from the family Sicariidae containACCEPTED phospholipases D (also referred to as sphingomyelinase D, with the later term being less favourable (Dantas et al., 2016)), which is considered to be the causative agent of and erythrocyte lysis (Foradori et al., 2005; Kuhn-Nentwig et al., 2011). Phospholipase D is present and active in the venoms of different Hexophthalma, Loxosceles and Sicarius species and it can cause haemolysis and keratinocyte cell death (Lopes et al., 2013; Planas et al., 2015; Magalhaes et al., 2017). Medically relevant incidents are mostly

8 ACCEPTED MANUSCRIPT reported from the and caused by Loxosceles species, also known as recluse spiders, violin spiders or brown spiders (Wright et al., 1997; Malaque et al., 2002; Isbister and Fan, 2011). This could be due to the fact that some of the larger Loxosceles species live there in close proximity to humans and therefore bites are more likely to occur compared to other sicariid spiders that live in more remote places. The symptoms of Loxosceles bites can be classified as unremarkable, mild, dermonecrotic and systemic or viscerocutaneous (Vetter, 2008). In most cases, only unremarkable or mild manifestations are recorded. Necrotic wounds occur in about 30–60% of all cases, but are typically self-healing and do not leave scars even without medical treatment (Vetter, 2008). Systemic effects involve the vascular system and acute intravascular haemolytic anaemia is considered a hallmark feature of systemic envenomations (Isbister and Fan, 2011). In the most severe cases, acute renal failure can occur and can result in a fatal outcome. However, systemic symptoms are rare with an incidence of <1–10% of all Loxosceles bites (Vetter, 2008; Isbister and Fan, 2011). Dermonecrosis is often misdiagnosed and Loxosceles bites are frequently blamed for skin alterations that have other causes (e.g. bacterial infections). Thus many reports of supposed Loxosceles envenomations are not reliable and Loxosceles bites might be less harmful than often described (Nentwig et al., 2017). MANUSCRIPT A

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Figure 4. Potentially dangerous Sicariidae: (A) Loxosceles reclusa, (B) Sicarius thomisoides (Photographs by Bastian Rast).

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2.1.5 Genus Poecilotheria (family Theraphosidae; Fig. 5): Theraphosid spiders, also known as , spiders or bird-eating spiders, are the most popular arachnid pets and they are generally considered harmless to humans (Lucas et al., 1994; Isbister et al., 2003a). However, members of the Indian and Sri Lankan genus Poecilotheria were recently suggested to be of underestimated medical importance (Fuchs et al., 2014). Bites by Poecilotheria species can lead to severe, long lasting muscle cramps. Such symptoms typically occur several hours after the bite, last for one week on average, and are recorded in 58% of all bites (Fuchs et al., 2014). It is unknown why Poecilotheria bites lead to systemic symptoms more often than bites from other theraphosids. This might be simply due to a larger amount of injected venom as Poecilotheria species possess relatively large amounts of venom (Herzig, 2010). Poecilotheria venoms might also contain a higher proportion of toxin(s) responsible for systemic symptoms or such toxins could simply be absent in the venoms of other theraphosids.

Ahmed et al. (2009) suggested that other theraphosids might also be medically important. However, their conclusions are based on single case reports or non-verified, anecdotal reports from older literature (with some identities of theMANUSCRIPT suspected spiders remaining unclear, see also Ahmed et al., 2010), rather than on studies examining larger numbers of verified bites; thus, we did not include this study in our assessment.

ACCEPTED Figure 5. Potentially dangerous Theraphosidae: (Photograph by Tobias Hauke).

2.1.6 Genus Latrodectus (family ; Fig. 6): The so-called black-widow spiders of the cosmopolitan genus Latrodectus are of medical importance, particularly in warmer

10 ACCEPTED MANUSCRIPT regions of the world. Typically in about 50% of all Latrodectus bites severe pain is observed that lasts for two days on average. Other local effects such as redness or diaphoresis are also common. Systemic effects such as nausea, vomiting or headache are reported for about one third of bites. However, life-threatening symptoms are rare and affect only small children or elderly people (Müller, 1993; Isbister and Gray, 2003a; Isbister and Fan, 2011). In the USA, where members of the genus Latrodectus are widely distributed, about 23,000 incidents with Latrodectus species were reported to a national database during an observation period of eight years (Monte et al., 2011). Envenomation symptoms only occurred in about 42% of these cases and only 1.4% were considered severe with no fatalities being observed. We are aware that data from poison control centres are generated in part from the general public and therefore probably contain an inherent portion of misdiagnosis (Vetter and Furbee, 2006). Nevertheless, this study (Monte et al., 2011) still exemplifies that the great majority of Latrodectus bites are far less dangerous than their public reputation. The neurotoxic venom component α-latrotoxin, a large protein, is considered to be responsible for the symptoms observed in . Interestingly related compounds were isolated from other spiders of the family Theridiidae as well, in particular from the genus Steatoda (Kuhn-Nentwig et al., 2011). Bites of these spiders (as well as of Cryptachaea and Parasteatoda species, which were previously in the genus Achaearanea ) MANUSCRIPT were found to cause similar effects to Latrodectus species. However, the symptoms are less severe in occurrence (Isbister and Gray, 2003b) and we therefore do not consider other theridiid genera besides Latrodectus as dangerous spiders.

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Figure 6. Potentially dangerous Theridiidae: Latrodectus tredecimguttatus (Photograph by Bastian Rast).

2.2 Scorpions (order Scorpiones):

11 ACCEPTED MANUSCRIPT 2.2.1 Genera Androctonus, Buthacus, , Centruroides, , , , , and Tityus (family ; Fig. 7): According to secondary literature (Keegan, 1980; Kleber et al., 1999), several genera of the family Buthidae are considered dangerous as their stings can lead to severe systemic symptoms with effects on the cardiovascular or nervous system. Androctonus, Buthus, Leiurus and Mesobuthus are of medical importance in northern and the Near and Middle East, Hottentotta in south Asia, Parabuthus in , Centruroides in the southern USA, Mexico and , and Tityus in South America (Berg and Tarantino, 1991; Dehesa-Davila and Possani, 1994; Bergman, 1997; Otero et al., 2004; Chowell et al., 2006; Chippaux and Goyffon, 2008; Ozkan et al., 2008; Cesaretli and Ozkan, 2010; Dehghani and Fathi, 2012; Bucaretchi et al., 2014; Kularatne et al., 2015; Seiter et al., 2016).

Small peptide toxins that target ion channels, especially voltage-gated sodium channels, are considered the main active components in the venoms of these scorpions (Quintero- Hernandez et al., 2013). These toxins lead to neuronal excitation stimulating particularly autonomic centres. In cases of severe envenomations, the sympathetic excitation and release of catecholamine in plasma mediate severe systemic effects such as myocardial injury, pulmonary oedema or cardiogenic (Chippaux,MANUSCRIPT 2012; Isbister and Bawaskar, 2014).

Envenomation symptoms caused by Tityus species are well studied with more than 1,300 recorded incidents in Brazil in the region of Campinas. Typically, in about 80% of all stings, the symptoms are classified as only mild with local effects (e.g. pain or erythema). In ~3% of cases, no envenomation symptoms are observed and these are considered to be “dry” stings. Systemic effects occurred in 17% of all cases and 1.8% of these were classified as severe with possibly life-threatening manifestations (e.g. shock, cardiac or respiratory failure). One patient died due to a sting from . Life-threatening manifestations or fatalities occurred only in children younger than 15 years old (Bucaretchi et al., 2014). ACCEPTED The genus Buthacus is also reported as being responsible for severe envenomation symptoms (Kleber et al., 1999), although there are apparently no definite incidents described in the literature (Chippaux and Goyffon, 2008). However, a peptide isolated from the venom of Buthacus macrocentrus was found to have close sequence to the dangerous toxins of Leiurus quinquestriatus and was also shown to be lethal to mice (Caliskan et al., 2012).

12 ACCEPTED MANUSCRIPT We therefore consider it plausible that Buthacus stings might lead to severe envenomation symptoms.

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Figure 7. Potentially dangerous Buthidae: (A) Androctonus australis, (B) Buthacus yotvatensis, (C) Buthus elmoutaouakili, (D) Centruroides sculpturatus, (E) Hottentotta judaicus, (F) Leiurus jordanensis, (G) Mesobuthus nigrocinctus, (H) Parabuthus villosus, (I) Tityus serrulatus (Photographs by Tobias Hauke).

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2.2.2 Genus Hemiscorpius (family Hemiscorpiidae; Fig. 8): Members of the genus Hemiscorpius are considered the most dangerous scorpions in and (Chippaux and Goyffon, 2008; Shahi et al., 2015). Hemiscorpius lepturus is responsible for most fatal scorpion stings in Iran (Pipelzadeh et al., 2007) and a fatal envenomation of a 15-year old male as consequence of a Hemiscorpius acanthocercus sting has been described (Shahi et al., 2015). Chippaux and Goyffon (2008) mention Hemiscorpius as the only medical relevant scorpions apart from those of the family Buthidae. The venom is cytotoxic and can lead to pathological changes in blood and tissue (Mirakabbadi et al., 2007; Dehghani and Fathi, 2012). Recently a phospholipase D was isolated from the venom of H. lepturus . It was shown to be highly active and, as in sicariid spiders, it is considered the lethal dermonecrotic toxin in Hemiscorpius venom (Torabi et al., 2017).

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Figure 8. Potentially dangerous Hemiscorpiidae: Hemiscorpius falcifer (Photograph by Tobias Hauke).

2.2.3 Genus Nebo (family ; Fig. 9): Data for envenomations by scorpions from the genus Nebo are scarce and contradictory. In adults, only mild symptoms were reported following two provoked stings of N. hierichonticus in man (Rosin, 1969). In contrast, Annobil (1993) assigned severe manifestations with intravascular coagulopathy and intracranial haemorrhagesACCEPTED or pulmonary oedema and death in two children to stings of N. hierichonticus . Thus, we consider the genus Nebo as potentially dangerous. However, as the data are scarce and the described symptoms unusual for scorpion envenomations, we suggest treating this status with caution until further insights are published.

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Figure 9. Potentially dangerous Scorpionidae: Nebo omanensis (Photograph by Tobias Hauke).

3. Arachnids wrongly accused of being dangerous or with questionable status In addition to the aforementioned taxa, public media or certain text books (Bücherl, 1971; Habermehl, 1987) often list further arachnids as being potentially dangerous although there is no proof that these arachnids were actually involved in dangerous incidents with humans. Clinical studies have demonstrated that some of the wrongly accused genera are relatively harmless to humans. Herein we give an overview of some arachnids that are either wrongly accused as dangerous or that have a questionable stMANUSCRIPTatus.

3.1 Spiders (order Araneae): 3.1.1 Genera (family Actinopodidae) and Trechona (family ): Several mygalomorph genera, often referred to as trapdoor spiders, are occasionally described as potentially dangerous despite a lack of data to support such contentions. For example, Bücherl (1971) lists Actinopus and Trechona as dangerous spiders. However, recently published clinical studies found these genera to be harmless to humans with only relatively mild symptoms (e.g. local pain, minor oedema or erythema) attributed to bites by Actinopus or Trechona (Lucas et al., 1994). For several other mygalomorph trapdoor spiders it was also demonstratedACCEPTED that they only cause minor manifestations following human envenomations (Isbister and Gray, 2004b).

3.1.2 Genus Eratigena (family ): The so-called hobo spider, Eratigena agrestis (former agrestis ), originally distributed in Asia and Europe, was introduced to where it was suspected of causing necrotic wounds. However, recent studies

15 ACCEPTED MANUSCRIPT could not identify E. agrestis as a spider of medical concern in the USA and concluded that envenomations by this species do not cause necrotic lesions (Gaver-Wainwright et al., 2011; McKeown et al., 2014). It should be noted that although spiders of the genus Eratigena are widespread, and are particularly common in and around homes even in urban environments, there is not a single verified bite that confirms E. agrestis or other members of this genus as dangerous to humans (Vetter and Isbister, 2004; Nentwig et al., 2013).

3.1.3 Genus Badumna (family ): Black house spiders of the genus Badumna , originally distributed in Australia and Asia but now introduced to other continents (Kielhorn and Rödel, 2011), were also suspected as a cause of necrotic wounds. However, a study comprising 25 verified Badumna bites in Australia concluded that they are unlikely to cause necrosis. Local effects such as pain, puncture marks or erythema were found to be typical manifestations following Badumna bites (Isbister and Gray, 2004a).

3.1.4 Genus Cheiracanthium (family Eutichuridae): Bites by “yellow sac spiders” (Cheiracanthium spp.) are regularly noted as a cause of severe necrosis (Divito et al., 2009). However, such claims are not based on verified spider bites and the link between Cheiracanthium bites and dermonecrosis is dubious.MANUSCRIPT In contrast, more comprehensive clinical studies (including verified spider bites) from Aust ralia, Europe and North America did not reveal any signs of severe dermonecrosis following bites by Cheiracanthium species. Envenomations by spiders of the genus Cheiracanthium typically result in only local symptoms (e.g. pain, swelling, redness) (Vetter et al., 2006; Gnädinger et al., 2013; Nentwig et al., 2013; McKeown et al., 2014; Varl et al., 2017). These local symptoms can be compared to the effects of wasp stings, as they are often more pronounced than in many other harmless spiders, which might be explained by a relatively high concentration of histamine in the venom of Cheiracanthium species (Nentwig et al., 2013). It needs to be emphasized here that phospholipase D, which is considered the causative agent of necrotic spider envenomations, ACCEPTEDis absent in the venoms of Cheiracanthium species (Foradori et al., 2005).

3.1.5 Genus (family Hexathelidae): Spiders of the genus Macrothele are occasionally discussed as being potentially dangerous, although there are no studies available on envenomations caused by these spiders. Thus, this might only represent a precautionary view, as Macrothele is currently placed in the same family (i.e. Hexathelidae) as the dangerous funnel-web spiders of the genera Atrax , Hadronyche and Illawarra . However,

16 ACCEPTED MANUSCRIPT phylogenetic studies indicate that the family Hexathelidae is non-monophyletic and that Macrothele is actually not more closely related to Atrax , Hadronyche and Illawarra than to many other mygalomorph spiders (Hedin and Bond, 2006; Bond et al., 2012). Hence, we concur with other authors (Isbister and Fan, 2011) that Macrothele should not be considered potentially dangerous until contrary insights are published.

3.1.6 Genus Lampona (family ): White-tailed spiders of the genus Lampona received – and still receive today – much media attention in Australia as a presumed cause of severe dermonectrotic wounds. However, studies comprising more than 130 definite Lampona bites clearly debunked this perception as an urban myth. Actual envenomations by white-tailed spiders result in mostly minor local effects similar to those recorded from wolf spiders (family Lycosidae; under 3.1.7) (Isbister and Gray, 2003c; White and Weinstein, 2014).

3.1.7 Genus Lycosa, Hogna (both family Lycosidae): Some wolf spiders (family Lycosidae), particularly those in the genera Lycosa or Hogna , were considered dangerous in older literature (Bücherl, 1971) and they were occasionally blamed for necrotic wounds in the absence of verified bites to support such claims.MANUSCRIPT Newer literature from South America and Australia examining the clinical effects of lycosid bites in humans has proved these assumptions incorrect (Ribeiro et al., 1990; Isbister and Framenau, 2004). Mostly local symptoms such as pain or redness – but not necrosis – were seen after bites by members of the family Lycosidae, with only 7% of patients showing minor systemic effects (e.g. nausea) (Isbister and Framenau, 2004). The effects can be explained by mechanical injury rather than actual envenomation (Isbister and Framenau, 2004). More severe effects formerly attributed to lycosid bites, including necrosis, are likely due to misdiagnosed Loxosceles bites (Ribeiro et al., 1990).

3.2 Scorpions (orderACCEPTED Scorpiones): 3.2.1 Genus Bothriurus (family Bothriuridae): Kleber et al. (1999) mention stings by the genus Bothriurus as a cause of severe envenomations with effects on the cardiovascular system, while others do not consider these scorpions medically important (Chippaux and Goyffon, 2008). To our knowledge, no studies exist that evaluated the effects of Bothriurus envenomations and found these scorpions to be potentially dangerous. A recent study from suggests that Bothriurus are not medically important and it assigns dangerous

17 ACCEPTED MANUSCRIPT envenomations in this country exclusively to scorpions of the genus Tityus (de Roodt, 2014), although there are several known species of Bothriurus distributed in Argentina. Thus, we assume that more serious manifestations following scorpion stings, formerly assigned to Bothriurus in older literature, might in fact be due to misidentified Tityus stings. Notably, other members of the family Bothriuridae (e.g. Cercophonius squama in Australia) do not cause severe envenomations (Isbister et al., 2003b).

3.2.2 Genera Apistobuthus, Compsobuthus , Lychas , Microtityus , Odontobuthus, Orthochirus , Rhopalurus , etc. (family Buthidae): Most dangerous scorpions belong to the family Buthidae, whose members often have thin, forceps-like pedipalps ("pincers") and thick, strong ("tails"). However, this ”pedipalp--ratio” cannot be used as a general rule to distinguish between potentially dangerous and harmless scorpions, particularly since scorpions of the genera Hemiscorpius and Nebo do not show these body proportions and, conversely, not all buthids are considered dangerous. In fact, the potentially dangerous genera listed under 2.2.1 represent only a fraction of the Buthidae, the most species-rich and diverse scorpion family, while most other genera are not considered medically important (Chippaux and Goyffon, 2008). For example, one of the smallest known scorpion species belongs to this family (e.g. MicrotityusMANUSCRIPT minimus ), reaching only about 10 mm in total length; it has an aculeus (“stinger”) length of 0.6–0.7 mm (Kova řík and Teruel, 2014) and thus is probably too small to cause severe envenomations in humans (Chippaux and Goyffon, 2008). In Iran, a species of the genus Compsobuthus (i.e. Compsobuthus matthiesseni ) was identified as a scorpion that regularly stings humans (Dehghani et al., 2009), but no data are available on typical envenomation symptoms, leading to the conclusion that stings by these scorpions lead to mild or inconspicuous manifestations. In South America, stings by scorpions of the genus Rhopalurus are scarcely registered but available cases classified only mild manifestations (Fuentes-Silva et al., 2014). A comprehensive study on scorpion envenomations in Australia comprised several stings caused by LychasACCEPTED species. Mostly local symptoms and pain were recorded as typical manifestations of Lychas stings and it was concluded that these scorpions cannot cause severe or life-threatening envenomations in humans (Isbister et al., 2003b).

However, there are some buthid genera with a questionable status. For example, a study from identified Apistobuthus pterygocercus as a scorpion that regularly stings humans and this species was considered of medical importance (Al-Sadoon and Jarrar, 2003).

18 ACCEPTED MANUSCRIPT However, no concrete envenomation symptoms were assigned to stings of this scorpion and hence it is dubious whether members of the genus Apistobuthus might cause severe envenomations in humans. In a single case report, severe systemic symptoms including pulmonary oedema were attributed to a sting of (Razi and Malekanrad, 2008), but this publication does not contain information on whether it was a verified scorpion sting or not. A review of scorpion stings in Iran mentions one unpublished death assigned to a sting of Orthochirus scrobiculosus (Dehghani and Fathi, 2012) but again no further information is provided in regards to proper identification of the scorpion. Due to their small body size and reluctance to sting (own observations; Dehghani and Fathi, 2012) we consider scorpions of the genus Orthochirus unlikely to cause severe envenomations in humans.

4. Assessment of the potential danger from arachnid envenomation Spiders and scorpions mainly prey on other and therefore the majority of their venom components do not target humans, which are not among their natural prey. However, some arachnids also prey on small vertebrates (Herzig and King, 2013), some have evolved toxins for defensive purposes (Inceoglu et al., 2003; Siemens et al., 2006; Osteen et al., 2016), and in some cases the molecular target of an arachnid toxin is similar in invertebrates and humans (Nicholson et al., 1998). This has leadMANUSCRIPT to the evolution of a small number of arachnid toxins that might cause severe envenomatio n effects in humans if injected in sufficient amounts. Although spider and scorpion venoms are a complex cocktail of diverse chemical compounds, in most cases small peptides that target ion channels are the main active components (with the large neurotoxic α-latrotoxins in the venoms of Latrodectus species and phospholipases D in sicariid spiders and the genus Hemiscorpius being notable exceptions) (Kuhn-Nentwig et al., 2011; Quintero-Hernandez et al., 2013). Thus, arachnid venoms typically exhibit a neurotoxic mode of action. In contrast, necrotic wounds following definitive spider bites or scorpion stings have only been recorded for genera containing high levels of active phospholipase D in their venoms (i.e., sicariid spiders and scorpions of the genus HemiscorpiusACCEPTED). Thus, phospholipase D activity seems to be a prerequisite for necrotic arachnidism. While pathogenic bacteria vectored by arachnids have also been discussed as a potential cause of necrosis associated with arachnid envenomations, a causal connection is unreasonable and unlikely (Vetter et al., 2015).

19 ACCEPTED MANUSCRIPT Given the small size of most arachnids (e.g., compared to venomous ), their venom glands and corresponding venom yields are comparatively small. Furthermore, only arachnids with fangs or stingers large enough to penetrate human skin can cause serious envenomation. Consequently, their small size renders most arachnids harmless to humans. Even large arachnids with venom toxins that could potentially harm humans often pose no threat, as their venom is used sparingly because of its high metabolic cost (Nisani et al., 2012; Morgenstern and King, 2013). For example, widow spiders of the genus Latrodectus only bite when massively threatened or accidentally squeezed (Nelsen et al., 2014); their preferred option is fleeing from the potential threat. Other means of defense in arachnids include playing dead, using their pincers (in the case of scorpions), striking with the front legs, producing hissing sounds, spreading of urticating hairs (e.g. theraphosid spiders), and even dry bites or stings. In the case of Latrodectus hesperus , up to 50% of all bites are “dry” (i.e. bites without venom injection) (Nelsen et al., 2014). Besides the presence of -active venom components and the injected venom amount, other factors can play an important role towards the severity of envenomation symptoms as indicated in Table 1.

Variable factors

Toxicity for vertebrates MANUSCRIPT Injected venom amount Size Arachnid Sex Age Geographical location Season Size/weight Sex Victim Age Health condition Route of injection (i.v., i.m., etc.)

Table 1 : SummaryACCEPTED of variable factors (adapted from Pucca et al., 2015) within the arachnid and the victim that can determine the severity of envenomation symptoms.

As evidenced by extensive clinical studies, only a low percentage of bites and stings from arachnids that are considered extremely dangerous result in severe systemic effects

20 ACCEPTED MANUSCRIPT (Bucaretchi et al., 2000; Isbister and Gray, 2003a; Bucaretchi et al., 2014; Isbister and Bawaskar, 2014). In most cases, only local manifestations (pain, redness, etc.) or no symptoms at all are recorded (e.g. >90% of all Phoneutria bites (Bucaretchi et al., 2000)). Severe systemic effects are mainly observed in children, presumably due to their lower body weight or due to their immune system not being fully developed (Bucaretchi et al., 2000; Bucaretchi et al., 2014). While after spider bites only very small children are typically affected by the most severe symptoms, scorpion envenomations can frequently lead to severe effects even in larger children up to an age of 15 years (Bucaretchi et al., 2014; Pucca et al., 2015; Shahi et al., 2015). Interestingly, in case of spider bites larger children were found to have fewer systemic envenomations than adults and the average duration of the clinical symptoms was also reduced (Isbister, 2004b). For many arachnids that cause severe human envenomations, are available. However, due to potentially severe side effects such as allergic reactions, antivenom should only be applied as a last resort if conventional treatment of the symptoms is not sufficient. In regards to Latrodectus antivenom there is an ongoing scientific debate about its efficacy. Some authors have questioned the efficacy (Isbister et al., 2014; Ryan et al., 2017) while others still regard it as the most efficacious therapy available based on symptom resolution, need for subsequent therapy, and hospital admission rates (Monte, 2012; White, 2017). In aMANUSCRIPT modern clinical setting, antivenom therapy is rarely used for arachnid envenomations; for exam ple, only 2% of all Phoneutria bites were treated with antivenom (Bucaretchi et al., 2000).

However, besides the percentage of serious envenomations, the incidence of bites and stings is also important for assessing the potential danger of arachnids. In their countries of origin, most bites and stings only happen when humans actively pick up the arachnids or accidentally get in contact with them (e.g. during garden work or when putting on clothing, in which arachnids have been hiding). Not surprisingly, the majority of arachnid bites and stings target the extremities (Bucaretchi et al., 2000). In the case of Phoneutria and Australian funnel-web spiders,ACCEPTED most bite incidents are caused during mating season by wandering males (Bucaretchi et al., 2000; Isbister and Gray, 2004b). The numbers of lethal envenomations by arachnids are dwarfed by the global death toll from bites and anaphylaxis caused by hymenopteran stings (Arnold, 2016; Welton et al., 2017). Nevertheless, in some cases arachnids can be quite abundant in densely populated areas, which increases the likelihood for accidental contact with humans. Thus there are regions such as northern Africa, the Near and Middle-East, Mexico, the Amazonian basin or southern Brazil with many human

21 ACCEPTED MANUSCRIPT encounters particularly with dangerous scorpions, resulting in a relatively high total number of envenomations. Worldwide, the estimated number of scorpion stings exceeds 1.2 million leading to more than 3250 deaths annually (Chippaux and Goyffon, 2008). While this study confirms the low percentage of fatal envenomations (i.e. 0.27%), it also clearly exemplifies that a high total number of encounters in combination with a low percentage of serious or fatal envenomations can still result in a significant problem for the health system in the countries of origin. However, it is assumed that by an improvement of the therapeutic management in those regions the lethality could be reduced very significantly (Chippaux and Goyffon, 2008). The situation for arachnids that are kept as pets is yet entirely different to the situation in their countries of origin. The majority of arachnid pet owners are reasonably well educated regarding the risks of keeping arachnids and therefore avoid direct contact. Pet arachnids are usually kept under controlled conditions in enclosed containers, minimising the risk of accidental contact. Furthermore, the surprise factor is eliminated as the owners are aware of the potentially dangerous arachnids they keep. All of these factors combined result in a fairly low incidence for envenomations from pet arachnids. According to our knowledge, there has not been a single documented case of a fatal envenomation by a pet arachnid, despite the continuous growth of the arachnid pet scene in Europe, America and Asia in the last few decades. MANUSCRIPT

In attempting to compile a catalogue of potentially dangerous arachnids, we decided to base the list on the genus rather than species level. The reason for this is that closely related species most likely have closely related toxins, so if one species from a certain genus has a toxin that causes severe effects in humans, a related species from the same genus is likely to contain either the same or a closely related toxin with similar activity. Hence, even if only one or a few species from a genus have a clinical track record for severe envenomations, we have still included the entire genus in the list as a precaution. Absence of evidence is not evidence of absence, so if there are no serious incidents recorded for a certain species, it does not mean that thisACCEPTED species does not have the potential to cause severe effects. It could, for example, reside in a remote geographic area and rarely come into contact with humans. However, we are aware that basing our list on the genus level might lead to an overestimate of the total number of dangerous arachnids, as some species within a genus classified as dangerous might be too small to produce a sufficient amount of the toxin responsible for adverse effects in humans or their fangs might be too small to penetrate human skin or they could simply lack toxins that are active in humans. Our proposed list of "dangerous

22 ACCEPTED MANUSCRIPT arachnids" that have the potential to cause severe envenomation in humans includes the following genera:

Spiders: Missulena (family Actinopodidae), Phoneutria (Ctenidae), Atrax, Hadronyche, Illawarra (all Hexathelidae), Hexophthalma , Loxosceles, Sicarius (all Sicariidae), Poecilotheria (Theraphosidae), Latrodectus (Theridiidae).

Scorpions: Androctonus, Buthacus, Buthus, Centruroides, Hottentotta, Leiurus, Mesobuthus, Parabuthus, Tityus (all family Buthidae), Hemiscorpius (Hemiscorpiidae), Nebo (Scorpionidae).

Note that dangerous arachnids are spread across several different families and thus no general rule of thumb can be given for differentiating dangerous from harmless spiders and scorpions. In case of doubt we suggest consulting an expert with taxonomic knowledge to identify the arachnid in question.

Spider family Dangerous genera Number of species Actinopodidae Missulena 17 Ctenidae Phoneutria MANUSCRIPT8 Atrax 3 Hexathelidae Hadronyche 31 Illawarra 1 Hexophthalma 6 Sicariidae Loxosceles 116 Sicarius 21 Theraphosidae Poecilotheria 14 Theridiidae Latrodectus 31 Total dangerous spider species 248 Total spider species 46,778 Potentially dangerous spiders 0.5%

Scorpion familyACCEPTED Dangerous genera Number of species Androctonus 28 Buthacus 24 Buthus 51 Buthidae Centruroides 91 Hottentotta 49 Leiurus 11 Mesobuthus 14

23 ACCEPTED MANUSCRIPT Parabuthus 33 Tityus 212 Hemiscorpiidae Hemiscorpius 15 Scorpionidae Nebo 9 Total dangerous scorpion species 537 Total scorpion species 2,322 Potentially dangerous scorpions 23.1%

Table 2: Summary of the number of arachnid species within spider and scorpion genera (in alphabetical order based on family/genus) that are considered potentially dangerous. The data was extracted from the World Spider Catalog (2017; http://www.wsc.nmbe.ch/) and The Scorpion Files (Rein, 2017; https://www.ntnu.no/ub/scorpion-files/index.php; both accessed on 25. July 2017).

5. Conclusions In summary, due to various reasons such as their small size, lack of vertebrate-active toxins, or their cryptic way of life, the great majority of arachnids are not capable of causing severe envenomations in humans. Even those few species of scorpions and spiders that are capable of causing severe effects in humans only induce minor local symptoms in the majority of cases. While some countries of origin of potentiall MANUSCRIPTy dangerous arachnids still have high total numbers of envenomations, the situation with pet arachnids is quite different. We propose that the combination of a low total number and a low percentage of serious envenomations will only result in a minor risk caused by pet arachnids. And due to modern medical care, lethal envenomations by arachnids are rare (Isbister and Fan, 2011). We conclude that the problem of arachnid envenomation is exaggerated in the public media. However, even a single lethal case is too much if it is preventable. We have therefore compiled a list of dangerous arachnids that have the potential to cause severe envenomations in humans. This list includes 10 spider and 11 scorpion genera and should serve as a guideline for regulatory authorities that want to take action to protect their citizens. As indicated in Table 2, there are currently 248 spiderACCEPTED and 537 scorpion species listed within those genera, comprising 0.5% of all extant spiders and 23.1% of all scorpion species (Rein, 2017; World Spider Catalog, 2017). Nevertheless, the actual number of dangerous arachnid species is probably much lower, as many species are only listed as a precaution based on their close taxonomic relationship to potentially dangerous species, despite a lack of concrete reports on severe

24 ACCEPTED MANUSCRIPT envenomations. In conclusion, only a small percentage of scorpions and a minute percentage of all spiders can be considered potentially dangerous to humans.

Disclosure statement Parts of this review were previously published in German in the journal Arachne as an expert opinion for the government of North Rhine-Westphalia, Germany (Hauke et al., 2015).

Acknowledgements The authors thank Volker von Wirth (Deutsche Arachnologische Gesellschaft e.V., Zülpich, Germany) for his contribution to the expert opinion about dangerous arachnids for the government of North Rhine-Westphalia, Germany (Hauke et al., 2015), Samantha Nixon (Brisbane, Australia) for comments on the manuscript, Bastian Rast (Tägerig, Switzerland) and Michael Gray (Australian Museum, Sydney, Australia) for outstanding photographs of arachnid specimens, and Alexander Ullrich (Munich, Germany) for providing scorpions for photography.

MANUSCRIPT

ACCEPTED

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31 ACCEPTED MANUSCRIPT Ethical Statement This work reported in this manuscript complied with all institutional, state, and national policies governing the ethical treatment of the experimental subjects. Moreover, we wish to acknowledge that:

(i) the material has not been published in whole or in part elsewhere;

(ii) the paper is not currently being considered for publication elsewhere;

(iii) all authors have been personally and actively involved in substantive work leading to the paper, and will hold themselves jointly and individually responsible for its content.

Tobias J. Hauke Volker Herzig

MANUSCRIPT

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