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Community science has contributed significantly to biodiversity and conservation related research. iNaturalist is a popular community science application, where community-submitted photo documentation of observed taxa has led to a large natural history database. Here, we present results of an iNaturalist project focusing on documenting Opiliones introduced to the USA and Canada. Including all observations made in this project up through 31 December 2021, there were 849 total observations (486 research grade), which included 16 introduced species (excluding multiple species of uncertain status), 11 of which were newly recorded for the USA and Canada. We provide an updated checklist of introduced species, including updated distributions for previously recorded species. This research was facilitated by the community science platform iNaturalist, which allows easy interactions between scientists of all types.

Female chemical signals are crucial for sexual communication in spiders and convey detailed information about females' mating status or age. However, evidence for chemical communication in spiders is largely behavioral. Only a few spider pheromones are known and quantitative chemical analyses of individual spiders are especially scarce. In the European wasp spider, Argiope bruennichi (Scopoli, 1772), females emit the volatile trimethyl methylcitrate, which attracts males from a distance. A recent study on the role of this pheromone in close-range male mate choice revealed that older virgin females approaching oviposition produce higher amounts of pheromone than younger ones, thereby increasing their attractiveness to males, and stop pheromone signaling shortly after copulation. Here we provide more detailed analyses of temporal dynamics in pheromone production in both virgin and mated female A. bruennichi. Our results corroborate previous observations indicating that male mating behavior in this species is guided by variation in female signaling effort.

Patterns of phototaxis are incompletely characterized in arachnids and hardly generalizable because of large variations in orders, families, species, environments, and methods employed. In a neotropical forest of French Guiana, we tested the effect of both light and diameter on pitfall trap catches. Light had a significant effect on capture rates of all arachnids and on Araneae alone, with more individuals caught in lit traps. Without light, pitfall diameter had no effect on capture rates, while in lit traps, significantly fewer individuals were captured only in smaller traps. Light trapping is thus a promising tool to complete inventories in tropical forests. This field experiment calls for further studies of the mechanisms by which arachnids are attracted by light, especially by unraveling an actual phototaxis from indirect effects like prey attraction.

Specialists possess specialized trophic adaptations. Spiders of the genus Palpimanus Dufour, 1820 are araneophagous spiders which also catch alternative prey. They have morphological, behavioral, and venomic adaptations tuned to higher efficacy in the capture and processing of other spiders. Here, we tested the hypothesis whether Palpimanus can develop on two prey types. We reared spiderlings of Palpimanus spp. on a diet composed of spiders and of insects, and recorded their performance. We found that Palpimanus exhibited significantly higher mortality on the insect diet. In fact, only spiderlings on the spider diet were able to develop. The developmental rate was slow, as one instar lasted on average more than 60 days. On the basis of this finding, we estimated that the life cycle is at least biennial. We conclude that Palpimanus spiders possess specialized prey-capture adaptations towards spider prey which prevent them to utilize alternative prey.

Water conservation is one of the major challenges encountered by terrestrial arthropods; species inhabiting dry forests are hypothesized to have adapted to dry conditions. Tityus pusillus Pocock,1893 is one of the most abundant scorpion species in northeastern Brazil, occurring in dry and tropical rainforests. Considering the wide distribution of T. pusillus, we aimed to investigate differences in desiccation resistance between populations originating from the Atlantic rainforest and the Caatinga dry forest. In this study, 40 individuals of T. pusillus from each of the two ecosystems were used. The two groups were separated into control and treatment groups (individuals without a water supply). Scorpions from the Atlantic rainforest had a shorter lifespan than those from the Caatinga dry forest, both in the control and treatment groups. However, the weight loss rate was higher in scorpions from the Caatinga dry forest than those from the Atlantic rainforest. In addition, Atlantic rainforest scorpions presented a lower resistance to desiccation, exhibiting a higher mortality rate than the Caatinga dry forest individuals. These results suggest that T. pusillus can exhibit, via phenotypic plasticity or local adaptation, a broad range of tolerances that allow it to persist in different habitats. Furthermore, our findings suggest that T. pusillus individuals from the Caatinga dry forest have physiological attributes that allow them to resist prolonged desiccation, which may be related to adaptations that are intrinsic to the population from the dry forest.

Pseudoscorpions are arachnids featuring three nymphal instars before reaching the adult age. Instars can be mostly recognized based on the number of trichobothria which lie along the chelal axis: as the individual grows, further trichobothria are added. The study of the post-embryonic growth based on trichobothria position has been the most widely used approach. However, other body parts can be subjected to particular growth patterns that need to be explored to fully understand post-embryonic development processes. Rigorous numerical approaches that allow meaningful statistical inference within growth regressions are now available. The recently described Mediterranean species Geogarypus italicus Gardini, Galli & Zinni, 2017 gave the authors the chance to review studies carried out in the past with the modern statistical approach mentioned above. Results confirm the main hypothesis about the growth process of the chelal axis but showed some differences that may be related to taxonomical aspects. Moreover, the study of body allometry during postembryonic growth showed that not all body parts undergo the same trend from protonymphs to males, on one side, and to females, on the other. Finally, the study of proportions between body parts through the analysis of ratios between their linear measurements pointed out a marked sexual dimorphism of pedipalps in spite of similar sizes and proportions of other body regions. The analysis led us to think that more interesting information could come from applying this approach to multispecies studies.

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