New Insight Into the Evolutionary Arms Race Between Spider Egg Sac Pseudoparasitoids and Active Maternal Care by the Spiders

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  New Insight Into the Evolutionary Arms Race Between Spider Egg Sac Pseudoparasitoids and Active Maternal Care by the Spiders ABSTRACT Pseudoparasitoids can lead to high mortality in spider egg sacs, and in some cases, they reduce the reproductive success of a spider female to zero. On the other hand, a species that develops within the spider's egg sac uses a limited resource derived from a single egg sac for its larval development. Therefore, the most crucial behaviour that increases the fitness of free-living pseudoparasitoid females is choosing the best host for their offspring. We analysed various points of the counter-adaptations of the spider egg sac pseudoparasitoid and spiders exhibiting active maternal care, utilising the ichneumonid  Hidryta fusiventris  (Thomson, 1873) and the wolf spider  Pardosa lugubris  (Walckenaer, 1802). We showed that the oviposition decision of  H. fusiventris  is based on the spider's egg sac size and that the fema...

Predation of the slender opossum Marmosops caucae (Didelphimorphia, Didelphidae) on the venomous spider Phoneutria fera (Araneae: Ctenidae) in Amazonian Ecuador, with a dietary overview for the genus Marmosops

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Predation of the slender opossum Marmosops caucae (Didelphimorphia, Didelphidae) on the venomous spider Phoneutria fera (Araneae: Ctenidae) in Amazonian Ecuador, with a dietary overview for the genus Marmosops

Abstract

Small marsupials of the genus Marmosops are widely regarded as omnivore-insectivores, but quantitative information on their diets is fragmentary. Here, we report the first verified predation event of the highly venomous wandering spider Phoneutria fera by Marmosops caucae during a nocturnal survey in Amazonian Ecuador, and provide the most comprehensive synthesis to date of prey use within the genus, based on a literature review and participatory science observations. The synthesis yielded nine primary studies and three iNaturalist records offering diet data for six Marmosops species. Collectively, these records encompass 15 invertebrate orders and five vertebrate classes; Coleoptera and Hymenoptera dominate, whereas large arachnids occur only sporadically. The breadth and composition of prey spectra are best explained by local availability rather than dietary specialisation, underscoring the genus's behavioural flexibility. Our observation expands the known trophic interactions of Marmosops and highlights the need for experimental work on venom tolerance and potential ecological effects on spider guilds.
Guerrero-Campoverde, A., Viteri-Basso, E., Peñaherrera-R., P., & Cisneros-Heredia, D. F. (2025). Predation of the slender opossum Marmosops caucae (Didelphimorphia, Didelphidae) on the venomous spider Phoneutria fera (Araneae: Ctenidae) in Amazonian Ecuador, with a dietary overview for the genus Marmosops. Food Webs, e00418. https://doi.org/10.1016/j.fooweb.2025.e00418