In all cases, symptoms subsided within 48-72 h and no further complications were reported. Envenomations by S. nobilis seem to produce symptoms similar (but not identical) to those previously reported from other Steatoda sp. Considering their benign outcome, envenomations by S. nobilis should still be regarded as of moderate medical importance, requiring monitoring and pain management strategies.

Venoms are best known for their ability to incapacitate prey. In predatory groups, venom potency is predicted to reflect ecological and evolutionary drivers relating to diet. While venoms have been found to have prey-specific potencies, the role of diet breadth on venom potencies has yet to be tested at large macroecological scales. Here, using a comparative analysis of 100 snake species, we show that the evolution of prey-specific venom potencies is contingent on the breadth of a species’ diet. We find that while snake venom is more potent when tested on species closely related to natural prey items, we only find this prey-specific pattern in species with taxonomically narrow diets. While we find that the taxonomic diversity of a snakes’ diet mediates the prey specificity of its venom, the species richness of its diet was not found to affect these prey-specific potency patterns. This indicates that the physiological diversity of a species’ diet is an important driver of the evolution of generalist venom potencies. These findings suggest that the venoms of species with taxonomically diverse diets may be better suited to incapacitating novel prey species and hence play an important role for species within changing environments.

The venom-injecting forcipules of centipedes represent an evolutionary novelty that appeared in the centipede stem lineage more than 400 Ma. No other lineage of arthropods (or indeed of animals) has evolved claws for injecting venom from a pair of walking legs. However, little is known of the development, ultrastructure, or detailed function of centipede forcipules. Here, we provide comparative structural information on the venom duct apparatus that is the main functional system within each forcipule, based on scanning electron microscopy and transmission electron microscopy studies. We also give comparative developmental information, using DAPI staining, on embryonic forcipules from the four main centipede orders, including Scutigeromorpha. The photographs of Scutigera embryos we present are the first to be published for any species belonging to this order. The structure of the venom apparatus within each forcipule represents a discrete element of the novelty, whose origin requires a special explanation. This is in contrast to the novel external shape of the forcipules, which can be arrived at gradually by a series of changes from the starting point of a standard walking leg. Drawing on a proposed structural homology between venom glands and epidermal glands, we present a hypothesis of how the venom gland and duct may have arisen in evolution.

The noble false widow spider Steatoda nobilis originates from the Macaronesian archipelago and has expanded its range globally. Outside of its natural range, it may have a negative impact on native wildlife, and in temperate regions it lives in synanthropic environments where it frequently encounters humans, subsequently leading to envenomations. S. nobilis is the only medically significant spider in Ireland and the UK, and envenomations have resulted in local and systemic neurotoxic symptoms similar to true black widows (genus Latrodectus). S. nobilis is a sister group to Latrodectus which possesses the highly potent neurotoxins called α-latrotoxins that can induce neuromuscular paralysis and is responsible for human fatalities. However, and despite this close relationship, the venom composition of S. nobilis has never been investigated. In this context, a combination of transcriptomic and proteomic cutting-edge approaches has been used to deeply characterise S. nobilis venom. Mining of transcriptome data for the peptides identified by proteomics revealed 240 annotated sequences, of which 118 are related to toxins, 37 as enzymes, 43 as proteins involved in various biological functions, and 42 proteins without any identified function to date. Among the toxins, the most represented in numbers are α-latrotoxins (61), δ-latroinsectotoxins (44) and latrodectins (6), all of which were first characterised from black widow venoms. Transcriptomics alone provided a similar representation to proteomics, thus demonstrating that our approach is highly sensitive and accurate. More precisely, a relative quantification approach revealed that latrodectins are the most concentrated toxin (28%), followed by α-latrotoxins (11%), δ-latroinsectotoxins (11%) and α-latrocrustotoxins (11%). Approximately two-thirds of the venom is composed of Latrodectus-like toxins. Such toxins are highly potent towards the nervous system of vertebrates and likely responsible for the array of symptoms occurring after envenomation by black widows and false widows. Thus, caution should be taken in dismissing S. nobilis as harmless. This work paves the way towards a better understanding of the competitiveness of S. nobilis and its potential medical importance.

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