Text and illustrations by Tobias J. Hauke and Volker Herzig

“Love Bites“ – A new study on envenomations caused by spiders and scorpions kept as pets

Since at least the 1980s theraphosid spiders, commonly known as tarantulas, belong to the most popular invertebrates amongst “exotic” pets (Klaas, 1989). Other mygalomorph and araneomorph spiders (order Araneae) and several scorpions (order Scorpiones) also attracted some attention as pets. However, these pets are actually “venomous”, which means they utilize venom for subduing prey, but also for defending themselves against potential predators and larger "troublemakers" including us humans. Astonishingly, up to now there are hardly any systematic studies evaluating any potential dangers and risks associated with pet ownership of venomous arachnids. In our view, this lack of knowledge was misused in several regards, previously. On the one hand, suppliers and breeders of pet arachnids tend to understate any associated risks for increasing sales, thereby acting carelessly towards the buyers and future owners. On the other hand, opponents of the pet keeping hobby often exaggerated any potential dangers, which even led to poorly conceived restrictions to the hobby if these suggestions were followed by politicians. To bridge this apparent gap in knowledge, we therefore decided to perform a scientific analysis of bite and sting incidents caused by pet arachnids. We examined under which circumstances bites and stings from pet arachnids occurred and what the resulting consequences were. Our study was meanwhile published in Toxicon, an international peer-reviewed journal focusing on all aspects of venoms and toxins (Hauke & Herzig, 2021a). In the present article, we want to summarize our most important results and conclusions to make them available to a broader audience.

Results

The most important findings of the study are displayed graphically in the following slide-show:

Risk assessment for keeping pet arachnids

Besides, we provide a risk assessment for owners of venomous arachnids based on the data analyzed in our study. “Risk” is a rather mathematical term, representing the product of the two factors “likelihood of occurrence” and “adverse effects”.

If you keep spiders and scorpions in captivity at home, the likelihood of ever getting bitten or stung is apparently higher as if you wouldn’t keep arachnids at home. Nevertheless, our data indicate there are usually less than 20 bites/stings reported per year. Accordingly, the overall likelihood still appears to be low, considering that there are tens or even hundreds of thousands arachnid pet owners globally. And this likelihood could likely be further reduced, if simple precautionary measures are followed. As mentioned before, most bite/sting incidents occurred during active interactions with the corresponding arachnids. Thus, if handling would be completely avoided and maintenance works are simply performed with tools such as long forceps, we assume that the likelihood of ever getting bitten/stung would significantly decrease.

As adverse effects, mostly the envenomation manifestations have to be considered. Our data clearly shows that the great majority of cases exhibit rather mild manifestations. Only 10.5% of all cases required medical assistance and only 1.1% were classified as severe.

The low likelihood multiplied by the largely harmless manifestations in our opinion yields a relatively low risk associated with pet arachnid ownership. But, of course, you have to be aware that basically every hobby and (recreational) activity is associated with certain risks and dangers. For instance, in Germany alone, there an annual 16 human deaths caused by bees, wasps or hornets and almost 200 humans deaths due to accidents while doing sports or games (according to data from the German Federal Statistical Office). Most notably, despite being kept as pets for at least four decades, we are not aware of any fatal incident ever caused by a venomous arachnid kept as pet in captivity.

Prospects and future studies

Almost all case reports, which formed the database for our study, originated from the 21^st century or, in other words, from the last two decades. Interestingly, we could observe a clear decline (of 55%) in the number of reported cases from the previous to the more current decade. There are several different possibilities for the cause of this trend. For example, (1) the hobby of arachnid keeping, in general, could be in decline, (2) the arachnid owners could have become more careful in the recent years (e.g. by learning from the mistakes of others), or (3) there could be a different tendency by the affected people for reporting those cases – at least we obtained most of our case reports from tarantula/scorpion forums, but it seems that nowadays social media (e.g. Facebook) is more popular amongst internet users than the former forums. In order to elucidate the true reason for this tendency, it would be interesting to monitor future bite and sting reports. Accordingly, we created a platform on which bite and sting incidents can be reported continuously – please visit the project site for further information: Global survey on bites/stings by spiders, scorpions and centipedes

Furthermore, we would like to emphasize that this present study focused on the circumstances, the arachnid taxa involved as well as on the scope of potential outcomes of spider bites and scorpion stings from specimen kept in captivity. Our study was definitely not intended to replace case studies by medical professionals (such as previously published Ahmed et al., 2009 or Fuchs et al., 2014 & 2018), which examine clinical effects and symptoms in detail. However, we hope that our study might provide the basis to set all future case reports into a wider context.

Finally, our large database containing 354 cases, which we also published as an Excel table together with our research article (Hauke & Herzig, 2021a), may contain even more information that itself could form the basis for future studies and new interpretations, respectively. For example, commonalities or differences in envenomation symptoms for certain arachnids could be extracted, which could then be used for conclusions on the evolution of arachnid venoms or for the development of new therapies (Hauke & Herzig, 2021b).

Conclusions for the hobby “arachnid keeping”

We hope our study may also serve as a better basis for diverse decisions and judgements in future. There are several interesting and important aspects, which may be concluded for pet arachnid keepers, including…

· Most of the bite and sting incidents caused by captive arachnids happened during active interactions (e.g. handling, works for maintenance, etc.) by the actual owners. On the first glance this sounds trivial, but it still supports an important conclusion: when in ongoing political or medial discussions the introduction of stricter legislations (e.g. the prohibition of keeping exotic pets in captivity in general) are proposed, this is often ill-founded by the potential danger these animals may exhibit for the general public. However, this perspective seems to be clearly rebutted by our data, at least with respect to arachnids. In fact, only a very low percentage of the accidents was caused by arachnids that actually escaped and even in those cases only the respective owners themselves were affected – we are not aware of any case in which uninvolved third parties were ever harmed. On the other hand, we believe that pet owners should still obligate themselves – without the necessity of political restrictions – to provide more due care when keeping arachnids in captivity: as many incidents resulted from active interactions, simple precautionary measures (e.g. avoidance of handling, even of allegedly “calm” specimen; performing works for maintenance in the terrarium only with aid and protection means such as forceps and sturdy gloves) and the elucidation of the associated dangers may effectively help to minimize any potential risks.

· Apart from the majority of mild cases there were only four of the totally 354 incidents (≙ 1.1%) that were classified as severe envenomation. Notably, these severe cases were not caused by the so called “medically important” spiders (e.g. from the genera Latrodectus, Loxosceles, etc.) or scorpions (e.g. Androctonus, Tityus, etc.), but exclusively by tarantulas (i.e. family Theraphosidae), which are usually considered of minor medical importance in their respective countries of origin. In fact, “medically importance” mostly means that there are frequent encounters, for which people seek medical assistance (e.g. by calling an envenomation hotline or visiting a doctor) – however, those encounters don’t necessarily have to result in particularly more dangerous outcomes. Consequently, it is not just the venom, but there are several other factors including the relative abundance and the distribution of the arachnid contributing to the “medical importance” of a particular species. Many of the medically important spider and scorpion species are actually synanthropic, and accordingly they often appear near or even inside human houses. Conversely, some of the potentially dangerous species may still be medically less important only due to the fact that they occur in remote areas, have a cryptic lifestyle or are rarely encountered by humans for other reasons – and that may also apply for some tarantulas. Hence, the medical importance of certain arachnids in their respective countries of origin is apparently only a poor indicator for assessing the dangers and risks associated when keeping such animals in terrariums. A few tarantula species, such as those in the genus Poecilotheria, can indeed be considered as “potentially dangerous” (Hauke & Herzig, 2017), as it is also confirmed in our current study. Nevertheless, only a low percentage of bites and stings even by those “potentially dangerous” arachnids result in severe manifestations. Combined with the low likelihood of ever being bitten/stung by an arachnid that is kept under controlled conditions in a terrarium, the overall risk that those arachnids pose for humans still appears relatively low.

In summary, we recommend the introduction of guidelines and educational campaigns that aim to increase the safety of keeping arachnids in captivity for both keepers and kept specimen alike. Based on the currently available data, we do not see any need for more restrictive measures or even the total prohibition of arachnid pet ownership – in the worst case, this could even result in more negative than positive impacts (e.g. as campaigns for species conservation or research could also be impeded [Bjørn-Yoshimoto et al., 2020]).

Literature

Ahmed, N.; Pinkham, M. & Warrell, D. A. (2009): Symptom in search of a toxin: Muscle spasms following bites by Old World tarantula spiders (Lampropelma nigerrimum, Pterinochilus murinus, Poecilotheria regalis) with review. Qjm-Int. J. Med. 102, 851-857.

Bjørn-Yoshimoto, W. E.; Ramiro, I. B. L.; Yandell, M.; McIntosh, J. M.; Olivera, B. M.; Ellgaard, L. & Safavi-Hemami, H. (2020): Curses or cures: a review of the numerous benefits versus the biosecurity concerns of conotoxin research. Biomedicines 8, 235.

Fuchs, J.; von Dechend, M.; Mordasini, R.; Ceschi, A. & Nentwig, W. (2014): A verified spider bite and a review of the literature confirm Indian ornamental tree spiders (Poecilotheria species) as underestimated theraphosids of medical importance. Toxicon 77, 73-77.

Fuchs, J.; Martin, N. C. & Rauber-Luthy, C. (2018): A verified bite by Heteroscodra maculata (Togo starburst or ornamental baboon tarantula) resulting in long-lasting muscle cramps. Clin. Toxicol. 56, 675-676.

Hauke, T. J. & Herzig, V. (2017): Dangerous arachnids – Fake news or reality? Toxicon 138, 173-183.

Hauke, T. J. & Herzig, V. (2021a): Love bites – Do venomous arachnids make safe pets? Toxicon 190, 65-72.

Hauke, T. J. & Herzig, V. (2021b): Muscle spasms – A common symptom following theraphosid spider bites? Toxicon 192, 74-77.

Klaas, P. (1989): Vogelspinnen im Terrarium. Ulmer Verlag, Stuttgart, 148 Seiten.