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.

Supplementary tables

In this review, we report on harvestmen and spiders feeding on fungi, fruits, and seeds. Fungivory in harvestmen is widespread, with most reports referring to tropical species in the family Sclerosomatidae, which consume mainly small forest mushrooms (families Marasmiaceae and Mycenaceae). In contrast, consumption of fungal material by spiders apparently occurs only if airborne spores trapped in the viscid threads of orb-webs (e.g., Araneidae and Tetragnathidae) are ingested along with old webs prior to the construction of new webs. Consumption of fruit pulp by harvestmen is also widespread, with several records of Leiobunum spp. (Sclerosomatidae) feeding on Rubus spp. berries and other lipid-poor fruits in the Holarctic region. In Neotropical forests, harvestmen in the families Cosmetidae and Gonyleptidae feed on lipid-poor pulp of fallen fruits. Among spiders, we document several cases of synanthropic species opportunistically feeding on fruit waste (e.g., pieces of banana, papaya, watermelon, or orange pulp) inside houses or disposed in yards. Only one case of a spider feeding on a wild fruit in the field was found in our search. Finally, we report several cases of harvestmen and spiders feeding on elaiosomes or arils (i.e., lipid-rich seed appendages). In conclusion, harvestmen consume mushrooms, fruit pulp, seeds, and seed appendages more frequently than spiders probably because they are “solid food feeders”, which means they can ingest solid tissues by biting off small pieces. In turn, spiders are “fluid feeders” and feed on vegetable matter most frequently in the form of fluids (e.g., nectar, stigmatic exudate, plant sap, and honey dew), rather than fungal or plant tissues.

Spiders are usually found through all seasons in the subtropics, but little is known about their seasonality patterns and how they respond to abiotic factors, especially in species-rich regions such as Brazil. We investigated the seasonal variation in spider communities and the possible influence of abiotic factors (e.g., temperature, rainfall) on spider abundance, species richness and composition in subtropical riparian forest in four river basins. Changes in spider abundance among seasons differed between ontogenetic stages: there were more spiderlings in the autumn, and similar numbers of adults year round. Species richness, on the other hand, was highest in spring and summer. Species composition differed between seasons and river basins. Several factors may be behind diversity changes in the araneofauna among seasons, however, none of the abiotic factors evaluated showed a strong direct influence. Seasonal patterns varied, with different species having peaks in all three seasons but autumn. Seasonality is clear in these spider communities but not all patterns follow predictions from simple temperature changes.

A new species of giant trapdoor spider, Euoplos dignitas sp. nov. (family Idiopidae), is described from the Brigalow Belt of inland Queensland, Australia. Phylogenetic analysis of a six gene molecular dataset for the tribe Euoplini reveals that this species is sister to the spinnipes-group from eastern Queensland, and unrelated to a morphologically similar congener (E. grandis Wilson & Rix, 2019) that occurs further south in the Brigalow Belt. Both E. dignitas sp. nov. and E. grandis are very large, scopulate, plug door-building trapdoor spiders from transitional woodland habitats on vertosols (‘black soils’), with superficially similar females and strongly sexually-dimorphic ‘honey-red’ males. Information on the known biology and distribution of E. dignitas sp. nov. is summarized, and a conservation assessment is provided under the International Union for Conservation of Nature’s (IUCN) Red List Criteria, indicating that this species is likely Endangered.

A new genus and species of Neotropical Grassatores, Hevelia crucis gen. et sp. nov., is described and illustrated based on material of both sexes from Colombia. After comparison with the greater groups in Zalmoxoidea, especially the putative early derivative families Guasiniidae and Icaleptidae, this new taxon is considered a Zalmoxoidea incertae sedis, and seems to be related with Trypophobica Cruz-López et al., 2021 (currently in Icaleptidae, but which should be removed from this family) and Costabrimma Goodnight & Goodnight, 1983 (currently in Zalmoxoidea incertae sedis), both from Central America. Two species currently included in the zalmoxid genus Stygnoleptes Banks, 1913 from El Salvador are transferred to Trypophobica, creating the new combinations T. gibbera (Roewer, 1954) and T. sellata (Roewer, 1954). Two morphological structures for Zalmoxoidea are named here: mons cribellatus (sexually dimorphic porous prosomal and/or abdominal dorsal hillock) and elbow-spade (lanceolate blade apical in the truncus penis).

Temperature strongly shapes the physiology and distributions of ectotherms. Environmental extremes and the range of temperatures encountered can limit persistence. Further, thermal tolerance limits are thought to be one of the factors limiting the distributions of invasive species. The critical thermal maximum (CT_Max) and critical thermal minimum (CT_Min) are metrics frequently applied for defining upper and lower thermal tolerances, respectively. Temperatures contained within the boundaries of the CT_Max and CT_Min comprise the thermal tolerance range. In this study, we tested whether thermal tolerances differed between two native (Latrodectus hesperus Chamberlin & Ivie, 1935 and L. mactans (Fabricius, 1775)) and one invasive (L. geometricus CL Koch, 1841) widow species (Latrodectus Walckenaer, 1805). We separately tested if thermal tolerances differed by life stage and sex. Using species distribution modelling, we also tested if thermal extremes or temperature range most accurately correspond with current species occurrences in the United States. We hypothesized that Latrodectus geometricus would have lower thermal tolerance range and that minimum temperatures would most influence their present distributions since they presumably originated from a more equatorial climate. We found that CT_Min did not vary by developmental stage, but was highest in males. We found that the CT_Min and CT_Max of L. geometricus (3.2, 51.5 °C) and L. mactans (1.9, 52.4 °C) were higher than L. hesperus (-1.9, 49.6 °C). Males also had the narrowest thermal tolerance range in the three species examined. Lastly, we found that the highest performing distribution model was the one correlating minimum temperature with L. geometricus occurrences.

Animals use nests for various functions including laying eggs, raising young and gaining protection from predators. Social insect colonies provide rich microhabitats for various foreign inhabitants. Social spiders in the family Eresidae live in large, long-lasting colonies with a dense silken nest where spiders reside in complex capture webs. Social spider colonies contain several organisms apart from the host spiders, yet little is known about the foreign species and their roles. In this study, we cataloged foreign animals found in the nests and webs of the Indian social spider Stegodyphus sarasinorum Karsch, 1892 from different sites in India. We then examined the abundance and diversity of foreign spiders in adult and juvenile colonies, and the nature of interaction of foreign spiders with host S. sarasinorum spiders. We found spiders classified into nine families and insects classified into five orders and a few small vertebrate taxa associated with S. sarasinorum colonies. Adult S. sarasinorum nests and webs contained significantly more foreign spiders than juvenile colonies. However, diversity of foreign spiders did not increase with the number of host spiders. Additionally, we found that foreign spiders found inside the nests preyed on individual S. sarasinorum spiders. Our study sheds light onto the intriguing biology of nest- and web-associates of social spiders.

The family Lycosidae is one of the spider families with the greatest diversity of species and with varied and striking strategies. Studies on Neotropical wolf spiders have contributed new and valuable information to the field of sexual selection for several decades, having discovered cases that differ markedly from previously known patterns, not only for the family but for spiders in general. Here we provide a review of studies on reproductive biology of South American wolf spiders in recent decades, focusing on the subfamilies Lycosinae, Allocosinae and Sossipinae. The promising possibilities of the spiders of this family to test fundamental hypotheses in sexual selection and reproductive biology are highlighted, and we outline areas of particular interest for future studies. We hope that this review will inspire further studies on a broader range of wolf spider species in the Neotropics.

Deinopid spiders use highly specialized webs composed of a triangular non-sticky scaffolding (NS scaffolding) containing three radii and a modified orbicular web with a rectangular shape to capture prey. Spiders actively manipulate their webs to capture prey. We describe the web construction behavior of Deinopis cf. cylindracea and compare it and the shape of the sticky silk spiral (SS spiral) of other deinopid species using images in the literature and on the Internet. The web-building behavior in D. cf. cylindracea follows the pattern previously described for other species of Deinopis MacLeay, 1839. Web construction takes approximately 15 min in D. cf. cylindracea and has two stages: NS scaffolding construction and SS spiral construction. The final structure of the SS spiral has four closely spaced capture cords, five placed further apart, three near the top of the web, and two cords on the handles, making a total of 12. Other species of Deinopis have different numbers of cords. Finally, a novel finding is that the youngest spiders do not make webs with sticky lines, but instead use a simplified web to lunge forward, using only their legs to contact prey. To our knowledge, such behavior has never been described in this or any other group.

Describing the signals involved in sexual interactions is crucial to understand how mating and fertilization success is achieved. We analyzed sexual interactions in the gonyleptid harvestman Pachyloides thorellii Holmberg, 1878 to test the possibility of associations between female and male behaviors. For that purpose, we recorded 21 sexual interactions of P. thorellii under laboratory conditions and performed fine scaled analyses of the videos. We found three female pre-copulatory behaviors (“Mouth parts protrusion,” “Genital operculum opening,” and “Ovipositor eversion”) that seem to be related to sexual receptivity and cooperation with mating occurrence, and four copulatory behaviors (“Bucking,” “Pulling,” “Body lowering,” and “Leg II movements”) that could be indicating to the male that further stimulation is required or that mating is about to end. We also found that males use multimodal courtship displays that include the exchange of tactile and possibly chemical signals between sexes. This study shows that courtship and copulation in P. thorellii include intense information flow between sexes and female evaluation from the beginning until the end of the sexual interaction.

Vinegaroons are members of a guild of apex arthropod predators in the high desert grasslands of southeastern Arizona. Despite their importance as major predators in the ecosystem, almost nothing is known about their potential prey, predators, or competitors. We evaluated predator-prey relationships of vinegaroons and 30 species of potential prey, 27 species of potential predators, and the detailed interactions among three taxa of their apex predator guild. With few exceptions, vinegaroons overpowered and preyed on most potential prey within a suitable size range, were almost immune to predation, and appeared to be the dominant species in interactions with other predator guild members. Their most vulnerable life stages were the first two free-living instar stages, whereas adults and fourth instar individuals were not preyed on by any predators active in the same areas and times as vinegaroons. Third instar individuals were a crucial transition stage in which they had a few predators but also were large enough that they required capturing many prey items to grow sufficiently to molt to the fourth instar. In interactions among arthropod predators, the general observation was that when predation occurred, the larger individual usually prevailed irrespective of taxon. Cannibalism among adult and fourth instar vinegaroons does not occur under natural conditions in contrast to when they are placed together in artificial stressful situations. Cannibalism of the three smallest instars appears likely and might partially explain why they are solitary and spend minimal time foraging.

Group-living spiders are rare, and can be divided into multiple subcategories based on their tolerance of group mates. While social spiders are cooperative, colonial spiders are often antagonistic towards conspecifics. We examined colony dynamics in a colonial species, Philoponella republicana (Simon, 1891), focusing on aggressive behaviors to further understand this understudied species. We studied whether web region, sex ratio, web size, or spider size affected aggression. We also tested whether colony members discriminate against conspecific intruders, since this behavior, known as group closure, is prevalent in many other group-living animals but had not yet been tested in colonial spiders. Colony mates were often aggressive due to competition for limited resources, such as mates and orb webs, yet several characteristics of this species may reduce these competitive forces. First, female-biased secondary sex ratios appear to reduce male-male and female-male competition. Moreover, although some individuals defended orb webs, other areas in the communal web were not defended. Philoponella republicana also did not exhibit group closure. Our results further confirm that aggression between males decreases in colonies with more female-biased secondary sex ratios, and larger individuals correlate with a higher frequency of aggressive interactions. Moreover, we raise new questions concerning the evolutionary pressures that shape coloniality in spiders.

Supplemental Materials

Table S1.—Effects of inter-colony translocation treatment on responses of Philoponella republicana.  - Download file

Table S2.—Results of inter-colony translocation experiment. - Download file

Metabolism powers all of life's processes, making it fundamental to understanding organisms in nature. For many arachnids, however, we do not have direct measurements of either metabolic rate or the relationship between metabolic rate and body size (i.e., allometric scaling, an important determinant of metabolic rate). Here, we present the first measurements of metabolic rate and allometric scaling in a stridulating spined micrathena spider, Micrathena gracilis (Walckenaer, 1805). Since intraspecific variation in metabolic rate may provide insights into variation in energetically costly behaviors, we additionally explore the link between stridulation and metabolism in M. gracilis. Our data suggests a link between stridulatory behavior and allometric scaling, such that increased stridulation is associated with a weaker connection between body mass and metabolic rate. We discuss how links between energetics, expression of behavior, and body size inform our understanding of trait variation in these spiders.

Supplemental Materials

Figure S1.—Correlation between opisthosoma length and mass. Table S1.—Models for respiration ranked by AIC. - Download file

We describe two new Nesticus Thorell, 1869 from Walker County, Georgia, USA. Nesticus lula sp. nov. is known from two caves on the eastern edge of Lookout Mountain and N. cressleri sp. nov. is known from three caves on Pigeon Mountain. Morphological and molecular evidence indicates the distinctiveness of both species when compared to other Nesticus from the southern Appalachians. Nesticus lula has reduced eyes and N. cressleri is eyeless. Both species are of conservation concern, as they are known from only a handful of sites spanning extremely limited ranges. This work contributes to our understanding of cave biodiversity in Georgia and of the Nesticus radiation in the southern Appalachians.

We analysed the dead-wood characteristics that determine the presence of saproxylic pseudoscorpion species in remnants of riparian cloud forest. We examined 98 dead-wood pieces (70 logs and 28 stumps), and recorded tree species, decaying wood stages, presence of the pseudoscorpion Lustrochernes grossus (Banks, 1893) (Chernetidae) and the Bess beetle Helicus tropicus. In these wood samples we found 24 L. grossus and one chela. We recorded the highest number of individuals in Clethra mexicana (11), followed by Quercus corrugata (6) and Liquidambar styraciflua (6). In Annona cherimola and Trema micrantha, one chela and one female were recorded, respectively. The presence of this pseudoscorpion is likely due to its relationship with the Bess beetle, which coexists in decaying wood. The distribution of L. grossus in dead wood may also be influenced by tree species and stage of decay. Forest fragmentation and the extraction of firewood from the remnant riparian fragments of cloud forest are factors that could jeopardize the saproxylic pseudoscorpion species and other arthropod diversity associated with decaying wood in this threatened ecosystem.

Ballus Koch, 1850 is a beetle-like jumping spider genus encountered in montane evergreen rainforests of the Central and Uva Provinces of Sri Lanka. The taxonomic literature documents three species of the genus for the island. However, neither the taxonomic validity nor the systematics of any of the three species have been previously examined. We used nuclear and mitochondrial DNA sequences (28S rRNA, H3, COI) as well as morphological characters to investigate the genetic and taxonomic diversity of Ballus populations in Sri Lanka, including specimens from type localities. No Ballus specimens were found outside of the central highlands. Results of molecular species delimitation and morphological analysis suggest the presence of only a single species of Ballus in Sri Lanka. We therefore propose B. sellatus Simon, 1900 to be a junior synonym of B. segmentatus Simon, 1900, while B. clathratus Simon, 1901 remains a nomen nudum. Further, we discuss the implications of our results for conservation planning.

Animals may build nests socially to minimize the energy required for nest construction. Paratemnoides spp. pseudoscorpions evolved sociality independently from all other social groups, and colonies create silken multi-chambered nests in which they molt and raise young, analogous in form to the nests of some wasps and bees. Here we describe these nests and examine pseudoscorpion construction efficiency. Silk is generally energetically expensive and as such, we hypothesized that P. elongatus build nests of a structure that minimizes silk use, thereby maximizing nest construction efficiency. We measured the number of nest chambers, their perimeter, and their area, for 31 nests, calculated several metrics of nest architecture, and developed five alternative mathematical models describing other possible nest geometries. We found that real social pseudoscorpion nests are constructed with high efficiency, measured as wall length per internal area, approaching that of mathematical optima. We also found that these nests use less silk per capita than if the same chambers were built separately, i.e., if they were solitary. This indicates a direct benefit to group members. We compared observed nest architecture with five mathematical models of nest geometry and found that pseudoscorpion construction efficiency outperformed all non-cooperative models and rivaled that of a cooperative one approximating the honeycomb conjecture - a mathematical proof describing the most efficient way possible to divide a 2-dimensional plane. In summary, social pseudoscorpions design group nests with multiple chambers in a way that minimizes wall length per internal area and approaches the efficiency of honey-bee-like hexagon constructcion.