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03 Jul 2020
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The 'Noble false widow' spider Steatoda nobilis is an emerging public health and ecological threat

How the noble false widow spider Steatoda nobilis can turn out to be a rising public health and ecological concern

Recommended by based on reviews by Michel Dugon and 2 anonymous reviewers

"The noble false widow spider Steatoda nobilis is an emerging public health and ecological threat" by Clive Hambler (2020) is an appealing article discussing important aspects of the ecology and distribution of a medically significant spider, and the health concerns it raises.
By contrast to previous studies (Dunbar et al., 2018; Warell et al., 1991; Bauer et al., 2019; BBC 2013, 2018), this article, with its extensive media and scientific literature review, shows that S. nobilis (Thorell, 1875) is now an important health concern in Britain. Indeed, the author shows that the population of this spider has significantly increased, at least since 1990, in both southern Britain and Ireland where it has remained greatly under-recorded. In these areas, S. nobilis is now often the dominant spider on and in buildings, in places in which there is a high a risk of bites, some of which are likely to be severe, in humans, with these bites largely under-recorded. According to Clive Hambler "There is thus a possibility of bites being left without adequate rapid treatment and monitoring - with a low but non-trivial risk of necrosis or sepsis".
The author points that one of the reasons for the lack of awareness of the risk is that arachnologists typically have a conflict of interest between the conservation of the species they study and raising concerns about spiders. This may lead them to understate the risk. Clive Hambler therefore calls for a closer, appropriately weighted attention to the frequency and risk of bites, based on all the information available, rather than being "dismissive of the possibilities of bites and impacts simply because many media reports contain major errors or alarmism". He also argues that the British Arachnological Society’s guidance on "false widow spiders" "needs substantive revision, both in terms of the likelihood of bites and the severity of effects."
Indeed, the author demonstrates that many inaccuracies have been published (see Table 3 of his manuscript) and, for each, he provides a correction and/or an alternative opinion. At the end of this MS (see Table 4), he provides testable speculations and hypotheses. As he rightly points out, testing is very important to fuel the debate, because "It will be very difficult to get a balanced and proportionate debate and response for such a confused and emotive issue, especially with the many misleading popular reports." He also suggests that research will require interdisciplinary collaboration between experts in many domains, including pathologists, immunologists, clinicians, ecologists, arachnologists, psychologists, physiologists, climatologists and epidemiologists.
This preprint is clearly descriptive and speculative, but well-written, interesting and certainly useful in terms of a review of the biology, ecology, potential dangerousness and distribution of S. nobilis, particularly for future studies. There is no doubt that arachnologists, the medical community and the media will be interested in this article, which is intended to sound the alarm. Naturalists in general will also be interested in this manuscript because it is an original and successful attempt to increase knowledge about a particular taxon based on diverse information sources.
The structure of the MS is a bit odd, with a certain toing-and-froing between the ecology/biology/distribution of the spider and the risks, dangerousness and venom of bites, but this is not problematic, as shown by the reviews of the manuscript - three reviews (available below) were written, two by specialists in this noble false widow (Michel Dugon and another researcher who wished to remain anonymous).
Despite the controversy surrounding certain of the statements made in this article, I therefore strongly recommend it and look forward to seeing the identified research priorities addressed.


[1] Hambler, C. (2020). The “Noble false widow” spider Steatoda nobilis is an emerging public health and ecological threat. OSF Preprints, axbd4, ver. 4 peer-reviewed and recommended by PCI Zoology. doi: 10.31219/
[2] Dunbar J.P., Afoullouss S., Sulpice R., Dugon M.M. (2018) Envenomation by the noble false widow spider Steatoda nobilis (Thorell, 1875) - five new cases of steatodism from Ireland and Great Britain. Clin Toxicol (Phila). 56(6):433-435. doi: 10.1080/15563650.2017.1393084
[3] Warrell D.A., Shaheen J., Hillyard P.D., Jones D. (1991) Neurotoxic envenoming by an immigrant spider (Steatoda nobilis) in southern England. Toxicon. 29(10):1263-5. doi: 10.1016/0041-0101(91)90198-Z
[4] Bauer, T., Feldmeier, S., Krehenwinkel, H., Wieczorrek, C., Reiser, N. and Dreitling, R. (2019) Steatoda nobilis, a false widow on the rise: a synthesis of past and current distribution trends. NeoBiota 42: 19–43. doi: 10.3897/neobiota.42.31582
[5] BBC (2013). False widow spider bites footballer Steve Harris. Accessed 1 November 2018.
[6] BBC (2018). False widow spider infestation schools to remain shut. Accessed 19 December 2018.

The 'Noble false widow' spider Steatoda nobilis is an emerging public health and ecological threatHambler, C.<p>*Steatoda nobilis*, the 'Noble false widow' spider, has undergone massive population growth in southern Britain and Ireland, at least since 1990. It is greatly under-recorded in Britain and possibly globally. Now often the dominant spider on an...Arachnids, Behavior, Biogeography, Biological invasions, Conservation biology, Demography/population dynamics, Ecology, Medical entomology, Methodology, Pest management, Toxicology, Veterinary entomologyEtienne Bilgo2019-06-28 18:26:05 View
01 Jul 2020
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Sub-lethal insecticide exposure affects host biting efficiency of Kdr-resistant Anopheles gambiae

kdr homozygous resistant An. gambiae displayed enhanced feeding success when exposed to permethrin Insect-Treated Nets

Recommended by based on reviews by Thomas Guillemaud, Niels Verhulst, Etienne Bilgo and 1 anonymous reviewer

Malaria is a vector-borne parasitic disease found in 91 countries with an estimated of 228 million cases occurred worldwide during 2018. The 93% (213 million) of those cases were reported in the African Region (WHO 2019). Six species of Plasmodium parasites can produce the disease but only P. falciparum and P. vivax are the predominant species globally. More than 40 species of Anopheles mosquitoes are important malaria vectors (Asley et al. 2018). Intrinsic (genetic background, parasite susceptibility) and extrinsic (feeding host preference, host diversity and availability, mosquito abundance) factors affect the capacity of mosquitoes to vector the disease (Macdonald 1952). Malaria is prevented by chemoprophylaxis, vaccination, bite-avoidance and vector-control measures. The mainstays of vector control are long-lasting insecticide (pyrethroid) treated nets and indoor residual spraying with insecticides (Asley et al. 2018). The widespread use of pyrethroid insecticides forced the emergence of insecticide resistance in malaria vectors reducing the insecticidal effect. Mosquitoes can modify their behaviour avoiding insecticide contact and so potentially reducing vector control tools efficacy. In this sense, Diop et al. (2020) investigated whether pre-exposure to an Insecticide-Treated Net (ITN) modulates the mosquito ability to take a blood meal in Anopheles gambiae. By means of video recording experiments the authors analyzed how the feeding/bitting behaviour was affected by kdr mutation genotypes (homozygous susceptible – SS-, heterozygotes -RS- and homozygous resistant -RR-) when exposed to two different insecticides (permethrin and deltamethrin). According to the results, the blood-feeding success did not differ between the three genotypes in the absence of insecticide exposure. However, authors observed differences in the feeding duration and blood meal size. In example, RR mosquitoes spent less time taking their blood meal than RS and SS. On the other hand, RS mosquitoes took higher blood volumes than RR females. These differences can affect the mosquito fitness by decreasing/increasing the likelihood to be killed by the host defensive behavior or increase the oogenesis so enhancing fecundity. Regarding the effect of exposition to insecticides authors detected a strong relationship between kdr genotype and Knock Down (KD) phenotype when mosquitoes were exposed to Permethrin. Previously, the authors have evidenced that RR mosquitoes prefer a host protected by a permethrin-treated net rather than an untreated net and that heterozygotes RS mosquitoes have a remarkable ability to find a hole into a bet net (Diop et al. 2015, Porciani et al. 2017). With data here obtained, they demonstrated that kdr homozygous resistant An. gambiae displayed enhanced feeding success when exposed to permethrin ITN. The changes observed in the feeding/biting mosquito behaviour can affect their fitness shaping the evolution of the insecticide resistance in mosquitoes’ natural populations. Moreover, this may also alter parasite transmission dynamics by modifying vector/host interactions and so vector capacity.


World Health Organization (2019). World malaria report 2019. Geneva: World Health Organization; 2019. ISBN 978-92-4-156572-1
Ashley EA, Pyae Phyo A, Woodrow CJ (2018). Malaria. Lancet. 391(10130):1608‐1621. doi: 10.1016/S0140-6736(18)30324-6
Macdonald G (1952). The analysis of equilibrium in malaria. Trop Dis Bull 49: 813-828.
Diop MM, Chandre F, Rossignol M, Porciani A, Château M, Moiroux N and Pennetier, C. (2020). Sub-lethal insecticide exposure affects host biting efficiency of Kdr-resistant Anopheles gambiae. bioRxiv 653980, ver. 4 peer-reviewed and recommended by PCI Zoology. doi: 10.1101/653980
Diop MM, Moiroux N, Chandre F, Martin-Herrou H, Milesi P, Boussari O, et al. (2015) Behavioral cost and overdominance in Anopheles gambiae. PLoS ONE. 10(4):e0121755. doi: 10.1371/journal.pone.0121755
Porciani A, Diop M, Moiroux N, Kadoke-Lambi T, Cohuet A, Chandre F, et al. (2017) Influence of pyrethroïd-treated bed net on host seeking behavior of Anopheles gambiae s.s. carrying the kdr allele. PLOS ONE. 12(7):e0164518. doi: 10.1371/journal.pone.0164518

Sub-lethal insecticide exposure affects host biting efficiency of Kdr-resistant Anopheles gambiaeMalal Mamadou Diop, Fabrice Chandre, Marie Rossignol, Angelique Porciani, Mathieu Chateau, Nicolas Moiroux, Cedric Pennetier<p>The massive use of insecticide-treated nets (ITNs) has drastically changed the environment for malaria vector mosquitoes, challenging their host-seeking behaviour and biting success. Here, we investigated the effect of a brief exposure to an IT...Behavior, Ecology, Evolution, Medical entomology, Pesticide resistanceAdrian DiazAnonymous2019-05-29 19:40:25 View
10 Jan 2020
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Culex saltanensis and Culex interfor (Diptera: Culicidae) are susceptible and competent to transmit St. Louis encephalitis virus (Flavivirus: Flaviviridae) in central Argentina

Multiple vector species may be responsible for transmission of Saint Louis Encephalatis Virus in Argentina

Recommended by based on reviews by 2 anonymous reviewers

Medical and veterinary entomology is a discipline that deals with the role of insects on human and animal health. A primary objective is the identification of vectors that transmit pathogens. This is the aim of Beranek and co-authors in their study [1]. They focus on mosquito vector species responsible for transmission of St. Louis encephalitis virus (SLEV), an arbovirus that circulates in avian species but can incidentally occur in dead end mammal hosts such as humans, inducing symptoms and sometimes fatalities. Culex pipiens quinquefasciatus is known as the most common vector, but other species are suspected to also participate in transmission. Among them Culex saltanensis and Culex interfor have been found to be infected by the virus in the context of outbreaks. The fact that field collected mosquitoes carry virus particles is not evidence for their vector competence: indeed to be a competent vector, the mosquito must not only carry the virus, but also the virus must be able to replicate within the vector, overcome multiple barriers (until the salivary glands) and be present at sufficient titre within the saliva. This paper describes the experiments implemented to evaluate the vector competence of Cx. saltanensis and Cx. interfor from ingestion of SLEV to release within the saliva. Females emerged from field-collected eggs of Cx. pipiens quinquefasciatus, Cx. saltanensis and Cx. interfor were allowed to feed on SLEV infected chicks and viral development was measured by using (i) the infection rate (presence/absence of virus in the mosquito abdomen), (ii) the dissemination rate (presence/absence of virus in mosquito legs), and (iii) the transmission rate (presence/absence of virus in mosquito saliva). The sample size for each species is limited because of difficulties for collecting, feeding and maintaining large numbers of individuals from field populations, however the results are sufficient to show that this strain of SLEV is able to disseminate and be expelled in the saliva of mosquitoes of the three species at similar viral loads. This work therefore provides evidence that Cx saltanensis and Cx interfor are competent species for SLEV to complete its life-cycle. Vector competence does not directly correlate with the ability to transmit in real life as the actual vectorial capacity also depends on the contact between the infectious vertebrate hosts, the mosquito life expectancy and the extrinsic incubation period of the viruses. The present study does not deal with these characteristics, which remain to be investigated to complete the picture of the role of Cx saltanensis and Cx interfor in SLEV transmission. However, this study provides proof of principle that that SLEV can complete it’s life-cycle in Cx saltanensis and Cx interfor. Combined with previous knowledge on their feeding preference, this highlights their potential role as bridge vectors between birds and mammals. These results have important implications for epidemiological forecasting and disease management. Public health strategies should consider the diversity of vectors in surveillance and control of SLEV.

[1] Beranek, M. D., Quaglia, A. I., Peralta, G. C., Flores, F. S., Stein, M., Diaz, L. A., Almirón, W. R. and Montigiani, M. S. (2020). Culex saltanensis and Culex interfor (Diptera: Culicidae) are susceptible and competent to transmit St. Louis encephalitis virus (Flavivirus: Flaviviridae) in central Argentina. bioRxiv 722579, ver. 6 peer-reviewed and recommended by PCI Entomology. doi: 10.1101/722579

Culex saltanensis and Culex interfor (Diptera: Culicidae) are susceptible and competent to transmit St. Louis encephalitis virus (Flavivirus: Flaviviridae) in central ArgentinaBeranek MD, Quaglia AI, Peralta GC, Flores FS, Stein M, Diaz LA, Almirón WR and Contigiani MS<p>Infectious diseases caused by mosquito-borne viruses constitute health and economic problems worldwide. St. Louis encephalitis virus (SLEV) is endemic and autochthonous in the American continent. Culex pipiens quinquefasciatus is the primary ur...Medical entomologyAnna Cohuet2019-08-03 00:56:38 View