A new cave species of atyid shrimp of the genus Caridina H. Milne Edwards, 1837 was discovered during a survey of a subterranean habitat in southwestern Iran (Khuzestan Province, Tashan Cave). This is the first record of a cave atyid shrimp in Iran and the first documented occurrence of a Caridina species inhabiting sulphidic groundwater. Phylogenetic analyses and genetic distances support the status of Caridina tashanica sp. nov. as a distinct species, closely related to C. shahrazadae. Morphologically, the new species is characterised by reduced eyes and pigmentation, and by an extremely elongated rostrum with numerous teeth. Males have specific, triangular endopodite of pleopod I, and a rod-like appendix masculina of pleopod II with numerous long setae. Ovigerous females lay relatively large, oval, white eggs, which clearly indicate a landlocked life cycle. This study contributes to the knowledge of atyid shrimps in the Middle East and to the subterranean biodiversity of the sulphidic Tashan Cave ecosystem in Iran.

Coin spiders of the genus Herennia Thorell, 1877 are species-rich nephilids distributed across South, East, and Southeast Asia and Australasia. They are notable for ladder-shaped arboricolous webs, extreme sexual size dimorphism, and complex sexual behaviors. The most recent revision recognized 11 species, only 4 of which were described from both sexes. Here, we present a taxonomic revision integrating new morphological and molecular data and recognize 14 species. We describe three new species—H. eva Kuntner from Sulawesi, H. maj Kuntner from Vietnam, and H. tsoi Kuntner et al. from Taiwan—and document previously unknown males of H. oz Kuntner, 2005 from Australia and H. tone Kuntner, 2005 from the Philippines. We also extend the known distribution of H. papuana Thorell, 1881 from New Guinea to Australia. Although several molecular species-delimitation analyses suggest H. oz and H. etruscilla Kuntner, 2005 may be conspecific, consistent and diagnostic morphological differences support their recognition as distinct species. We provide an updated identification key to all valid Herennia species. Additional undescribed endemics are likely to occur across the Asian mainland and the rapidly disappearing forests of Southeast Asian and Australasian islands. The genus’ biogeographic pattern, shaped by an ancestrally broad distribution spanning the Wallace Line, may reflect repeated loss and regain of ballooning, a hypothesis that warrants experimental and comparative testing.

Pisauridae are a global and heterogeneous assemblage of spider genera with diverse morphologies and lifestyles. So far, the monophyly of Pisauridae and the inclusion of fishing spiders (Dolomedes) in this family have not been thoroughly tested. Here, we amend the systematics and classification of these lineages within a UCE phylogenomic framework and through a detailed morphological reappraisal. For estimations of their evolutionary age, we perform and compare outcomes from two divergence estimation approaches, an a posteriori likelihood, and an a priori Bayesian. Phylogenies reject the monophyly of both Pisauridae and Dolomedes: (1) Focal Clade I groups true Pisauridae genera including Pisaura; (2) Focal Clade II contains Blandinia and is sister to Trechaleidae and Lycosidae; (3) Focal Clade III groups Dolomedes, Megadolomedes, and Ornodolomedes, and is sister to Blandinia, Trechaleidae, and Lycosidae. We therefore propose to delimit Pisauridae by removing Dolomedidae rank resurrected (including Dolomedes, Bradystichus, Megadolomedes, Caledomedes, Mangromedes, Ornodolomedes, and Tasmomedes) and Blandinia incertae sedis. Likelihood and Bayesian time calibration approaches yield comparable divergence estimations: Pisauridae origin is estimated at 29-40 Ma; Blandinia 21-34 Ma; Dolomedidae 10-17 Ma; Dolomedes 9-16 Ma. Reconstructions suggest that the evolution of terrestrial and web-building lifestyles from semi-aquatic ancestors in Pisauridae coincided with cooling and drying climates during the mid-Miocene, but this was not the case in the few recent cases of terrestrialization in Dolomedes species. This historic reconstruction illustrates how climatic changes, or rapid radiation, can drive lifestyle diversification.

Major ampullate (MA) silk, synthesized by spiders, is tougher than most biological and synthetic materials. Orb weavers evolved some of the toughest MA silk, reaching extremes in bark spiders, genus Caerostris (Araneidae). Increased proline content is associated with tougher silk but may increase the metabolic cost. Transitions (phylogenetic/ontogenetic) to larger body sizes are expected to drive coevolution of tougher, costlier silk, because larger prey presents disproportionally higher kinetic energy. Interspecific shifts to tougher MA silk are documented, but intraspecific patterns are unknown, although spiders increase several hundred times in body mass through ontogeny. Small spiderlings prey on small insects and might not face the selection pressure on adults for capturing large prey. Additionally, extreme female-biased sexual size dimorphism in orb-weaving species like bark spiders results in sex-specific selection pressures for small versus large prey. We therefore ask whether species with exceptionally tough silk, like bark spiders, show different patterns in silk toughness between ontogenetic stages and sexes. We posed three hypotheses: H1, constrained silk production hypothesis; H2, sexually decoupled silk production hypothesis; H3, body size selection pressure hypothesis; and tested them by investigating the mechanical properties of MA silk among size classes and sexes in two Caerostris species from Madagascar, C. darwini Kuntner & Agnarsson, 2010 and C. kuntneri Gregorič & Yu, 2025. We found that only large females produce exceptionally tough silk with higher initial stiffness, while juvenile females and all males produce inferior silks. These results imply ontogenetic plasticity in Caerostris silk production and support the third hypothesis.

Madagascar is a biodiversity hotspot with high endemism and ancient phylogenetic diversity. We here report the discovery of Osmooka aphana gen. nov., sp. nov. from Marojejy National Park. Phylogenomic analyses place Osmooka as sister to the Australian Paraplectanoides Keyserling, 1886 and this doublet is sister to Nephilidae Simon, 1894. When proposed, Paraplectanoididae Kuntner, Coddington, Agnarsson & Bond, 2023 was exclusively Australian and monogeneric, but was predicted to contain additional, undescribed taxa. The discovery of Osmooka and its phylogenetic placement in Paraplectanoididae support this prediction. We present a taxonomic treatment of Osmooka and Paraplectanoides, and a reappraisal of Orbipurae morphological homologies. With this new discovery, we revalidate Paraplectanoididae, Nephilidae, and Phonognathidae Simon, 1894 ranks resurrected as exclusive, monophyletic, and well-diagnosed families, whereas Araneidae Clerck, 1757 requires further redefinition. Finally, we test the hypothesis of East Gondwanan vicariant origin of Osmooka and Paraplectanoides. This scenario would predict an ancient age of their ancestor, predating the 130 Ma breakup of Gondwana. Divergence dating refutes this hypothesis by estimating their common ancestor at 57 Ma. Rather than through vicariance, the disjunct distribution of Osmooka and Paraplectanoides is best explained through Cenozoic intercontinental dispersal and/or extinctions. Potential discovery of additional paraplectanoidid diversity might better elucidate the timing, modes, and trajectories of historic dispersal and extinction events.

Among terrestrial animals, spiders exhibit the most striking examples of sexual size dimorphism (SSD) but better understanding of its evolution requires improved taxonomy and phylogeny. Many sexually dimorphic spiders lack adequate description, phylogenetic placement, and natural history observations. In South Africa, we documented the natural history of a poorly known spider, Megaraneus gabonensis (Lucas, 1858), with extreme, female-biased SSD (eSSD, female:male approximately 4:1). Here, we redescribe M. gabonensis, place Megaraneus Lawrence, 1968 phylogenetically for the first time, assess whether the observed eSSD represents an independent evolutionary origin, and test whether the macroevolutionary pattern is better explained by male dwarfism or female gigantism. The recovered phylogenetic placement of Megaraneus in the araneid ‘backobourkiines’, a clade previously considered as restricted to East Asia and Australasia, extends the range of this clade to the Afrotropics. We find that eSSD was present in the common ancestor of the ‘backobourkiines’, with further increases in female body length occurring independently in Megaraneus, Backobourkia Framenau, Dupérré, Blackledge & Vink, 2010, and the currently misplaced Parawixia dehaani (Doleschall, 1859). We conclude that the evolution of eSSD reflects a complex pattern of sex-specific size changes across spider phylogeny, but that in Megaraneus it results from female gigantism.

We report a sequence of unusual male behaviors observed in Nephila pilipes (Fabricius, 1793) (Araneae: Nephilidae Simon, 1894), a sexually size dimorphic tropical spider species in Singapore. We documented a male suitor using his mouth parts (chelicerae) rather than his copulatory organs (pedipalps) to repeatedly probe female genitals. The behaviors may have served as a strategy to assess the female’s mating status, functioned as a courtship strategy, or, most plausibly, represented an attempt to remove a genital plug. The documented chrono-sequence culminated in the male’s attempted commensalism, followed by an aggressive attack by the female, resulting in near-fatal injury to the male. Notably, the attack did not escalate into cannibalism, suggesting that the extreme size difference in Nephila may render small males unappealing as prey.

Sexual cannibalism, a behavioral syndrome where one mating partner consumes the other before, during, or after copulation, is particularly widespread among spiders and often exemplifies sexual conflict. Female sexual cannibalism has driven the evolution of numerous male counter-adaptations. Here we review sexual cannibalism in spiders, evaluate five broad hypotheses explaining its evolution, and provide possible explanations for numerous male reproductive strategies associated with this behavior. These male strategies include mating with immature females, opportunistic mating with molting or feeding females, coercive mating, nuptial gifts, inducing female quiescence, thanatosis, mate binding, sperm transfer adjustments, catapulting, and remote copulation. We emphasize the importance of clearly defining these behaviors and advocate for greater experimental repeatability in future experimental and comparative research. The evolutionary dynamics of these strategies are discussed within the frameworks of sexual conflict, sexually antagonistic coevolution, sperm competition, and cryptic female choice. We call for future research to expand taxonomic sampling, standardize methodologies, integrate field-based observations/experiments, and quantify the costs and benefits for each sex. Such efforts are essential to contextualize sexual cannibalism within broader ecological and evolutionary paradigms.

The ideal free distribution (IFD) theory predicts that individuals are free to move among habitat patches and distribute among them “ideally,” in order to maximize individual evolutionary fitness. Size and quality of habitat patches then should directly impact the number of individuals occupying them, and connectivity of habitat patches likely plays a role if dispersal is limited. However, habitat patches can be distributed so that movement no longer can be considered free, for example, when patches are isolated. Challenges stemming from patch delimitation and detection rate of occupants further complicate efforts attempting to resolve such patterns. Here, we utilize as habitat patches the orb webs of four different populations belonging to three golden orb weaver spider species, Nephila pilipes (Fabricius, 1793), Nephilingis livida (Vinson, 1863), and Trichonephila clavipes (Linnaeus, 1767), and the obligate spider kleptoparasites (Argyrodinae, Theridiidae) that are associated with their webs. We examine how the IFD predicts the abundance of kleptoparasites under different patterns of patch size and distribution. We found that larger host webs, that is, habitat patches that contain more resources, are occupied by a higher number of kleptoparasitic spiders, regardless of their degree of isolation. Although the free movement prediction is often violated in natural systems, we find no evidence for habitat patch connectivity affecting the abundance of kleptoparasites, indicating that their dispersal ability facilitates the location and colonization of habitat patches regardless of their isolation. Therefore, our results support the interaction between argyrodine kleptoparasitic spiders and the webs of golden orb weavers to be a suitable natural system for studying the IFD.

Ants and termites are insect groups that make up most of the insect biomass in tropical ecosystems. Due to their social structure and abundance, they are some of the most bountiful prey available to other invertebrates such as spiders. However, ants and termites possess dangerous defense strategies, thus limiting their accessibility to general predators. Here, we report on an unexpected finding of a three-way predator-prey-kleptoparasite interaction in Madagascar among a termite Nasutitermes sp. (prey), a previously unknown theridiid spider Vigdisia praesidens gen. nov., sp. nov. (predator), and an ant Pheidole spinosa (kleptoparasite). Our field observations suggest that the spiders are able to detect a damaged termite nest from a distance to disperse onto it and prey on its residents. Kleptoparasitic ants also arrive on the scene to steal from the spiders their termite prey. Both the spider and the ant seem to possess some degree of behavioural prey specialisation for Nasutitermes termites. The here described ecological interaction warrants further study to better understand the exploitation of signals by such phylogenetically diverse arthropods.

Madagascar is a global biodiversity hotspot, but its biodiversity continues to be underestimated and understudied. Of raft spiders, genus Dolomedes Latreille, 1804, literature only reports two species on Madagascar. Our single expedition to humid forests of eastern and northern Madagascar, however, yielded a series of Dolomedes exemplars representing both sexes of five morphospecies. To avoid only using morphological diagnostics, we devised and tested an integrative taxonomic model for Dolomedes based on the unified species concept. The model first determines morphospecies within a morphometrics framework, then tests their validity via species delimitation using COI. It then incorporates habitat preferences, geological barriers, and dispersal related traits to form hypotheses about gene flow limitations. Our results reveal four new Dolomedes species that we describe from both sexes as Dolomedes gregoric sp. nov., D. bedjanic sp. nov., D. hydatostella sp. nov., and D. rotundus sp. nov. The range of D. kalanoro Silva & Griswold, 2013, now also known from both sexes, is expanded to eastern Madagascar. By increasing the known raft spider diversity from one valid species to five, our results merely scratch the surface of the true Dolomedes species diversity on Madagascar. Our integrative taxonomic model provides the framework for future revisions of raft spiders anywhere.

Cave systems fed with hydrogen sulfide-rich groundwater are unique chemoautotrophy-dependent ecosystems. Although globally widespread and known to harbor unique subterranean metazoan communities, they have mostly been studied in Europe and North America, less so in Asia. Here, we report on a discovery of a new species of amphipod crustacean from sulfidic waters of Tashan-Chah Kabootari aquifer from Zagros Mountains in Iran. The new species corresponds morphologically to the melitid genus Tegano Barnard & Karaman, 1982, and Tegano tashanensis sp. nov. is the first amphipod from the superfamily Hadzioidea found exclusively in sulfidic water. Phylogenies derived from the mitochondrial coi and the nuclear 28S rRNA sequences recover T. tashanensis sp. nov. in a clade that contains representatives of the currently para- or polyphyletic genera Barnardomelita, Brachina, Josephosella , and Tegano indicating the need for a revised melitid genus level systematics. This clade comprises marine, freshwater and subterranean species globally distributed in regions that were connected by the ancient Tethys Sea. As such, these taxa may be suitable biogeographic models for studying past dispersal, vicariance and multiple colonization of inland groundwaters.

Mating plugs in animals are ubiquitous and are commonly interpreted to be products of mating strategies. In spiders, however, mating plugs may also take on functions beyond female remating prevention. Due to the vagaries of female genital (spermathecal) anatomy, most spiders face the problem of having to secure additional, non-anatomical, protection for transferred sperm. Here, we test the hypothesis that mating plugs, rather than (or in addition to) being adaptations for mating strategies, may serve as sperm protection mechanism. Based on a comparative study on 411 epigyna sampled from 36 families, 187 genera, 330 species of entelegyne spiders, our results confirm the necessity of a sperm protection mechanism. We divided the entelegyne spermathecae into four types: SEG, SED, SCG and SCD. We also studied detailed morphology of epigynal tracts in the spider Diphya wulingensis having the SEG type spermathecae, using 3D-reconstruction based on semi thin histological series section. In this species, we hypothesize that two distinct types of mating plug, the sperm plug and the secretion plug, serve different functions. Morphological details support this: sperm plugs are formed on a modified spermathecal wall by the spilled sperm, and function as a temporary protection mechanism to prevent sperm from leaking and desiccating, while secretion plugs function in postcopulation both as a permanent protection mechanism, and to prevent additional mating. Furthermore, with the modified spermathecal wall of S2 stalk, the problem of shunt of sperm input and output, and the possibility of female multiple mating have been resolved. Variation in spermathecal morphology also suggests that the problem of sperm protection might be resolved in different ways in spiders. Considering mating plugs of varying shapes and origins in the vast morphospace of spiders, we conclude that mating plugs might serve different purposes that relate both to mating strategies, as well as to sperm protection.

Pisauridae Simon, 1890 or "nursery web spiders" are a global and heterogenous assemblage of spider genera with diverse lifestyles, containing web builders and webless species, as well as terrestrial and semi-aquatic species, notably "fishing spiders", genus Dolomedes Latreille, 1804. Incomplete, unresolved, or conflicting phylogenies have so far hampered testing for Dolomedes and pisaurid monophyly and evolution. Here, we broadly address these questions within a phylogenomic and comparative framework. Our goals are i) reconstruction of a robust phylogeny to test the monophyly of Dolomedes and Pisauridae and to amend Dolomedes classification; ii) estimation of evolutionary shifts and trends in lifestyles and capture webs; and iii) evaluation of hypotheses of morphological trait association with a semi-aquatic lifestyle. To this end we generate subgenomic data (ultraconserved elements or UCE) for 53 Dolomedes species and 28 pisaurid genera. We analyze these data using maximum likelihood, Bayesian, and multi-species coalescence approaches, as well as using two different phylogenetic time calibration methods, RelTime and MCMCtree. Consistent across analytical approaches, our phylogenies reject the monophyly of both Pisauridae and Dolomedes. "Pisaurid" genera fall into three clades: 1) Focal Clade I groups the majority, including Pisaura Simon, 1886, hence representing true pisaurids; 2) Focal Clade II = Blandinia Tonini et al., 2016 is sister to Trechaleidae Simon, 1890 and Lycosidae Sundevall, 1833; 3) Focal Clade III with fishing and raft spiders groups Dolomedes, Megadolomedes Davies and Raven, 1980, and Ornodolomedes Raven and Hebron, 2018 and is sister to Focal Clade II, Trechaleidae, and Lycosidae. Our taxonomy, based on complementary taxa and morphological evidence, resurrects Dolomedidae Simon, 1876 to include Dolomedes and the Oceanic genera Bradystichus Simon, 1884, Megadolomedes, Caledomedes Raven and Hebron, 2018, Mangromedes Raven and Hebron, 2018, Ornodolomedes, and Tasmomedes Raven and Hebron, 2018. Both RelTime and MCMCtree analyses yield comparable divergence estimations: Pisauridae origin is estimated between 29 and 40 Ma; Blandinia between 21 and 34 Ma; Dolomedidae between 10 and 17 Ma; and Dolomedes between 9 and 16 Ma. In order to avoid misleading significant correlations and/or over-resolved ancestral states, we performed taxon sampling bias correction in all evolutionary analyses. Evolutionary analyses reconstruct semi-aquatic lifestyle as ancestral to a large clade containing pisaurids, lycosids, trechaleids, Blandinia, and dolomedids, with several reversals to terrestrial lifestyle. Capture webs evolved at least three times, with reversals. Counter to expectation, the evolution of lifestyles and capture webs are independent. Although leg and tarsus lengths do not indicate lifestyles, semi-aquatic taxa are significantly larger than terrestrial ones. We explain this pattern with a biomechanical threshold over which surface tension can be broken while spiders forage under water. Our time-calibrated analyses indicate that the evolution of terrestrial and web-building lifestyles from semi-aquatic ancestors in Pisauridae coincided with cooling and drying climates in the mid-Miocene. We therefore hypothesize that climatic changes have acted as strong selection pressures toward lifestyle diversification. ### Competing Interest Statement The authors have declared no competing interest.

Dolomedes may easily be considered to be among the most charismatic spider taxa. Known colloquially as fishing or raft spiders, this clade of dolomedid cursorial hunters is speciose with about 100 valid species names. Most Dolomedes are large spiders that inhabit water bodies across all continents except Antarctica and, interestingly, South America. Dolomedes have captured the attention of researchers and the public alike for their ability to walk on and submerge under water, fish for prey (including small vertebrates), and for their often-bizarre mating behavior that includes examples of male spontaneous death and sexual cannibalism. In this review, we critically evaluate what is known of Dolomedes biology, focusing on their systematics and morphology, ecology, behavior, and conservation. Given their close association with water, Dolomedes may be particularly vulnerable to the impacts of anthropogenic change and provide an important group of indicator species for understanding the effect of pollution, habitat loss and climate change. We outline a roadmap for future studies that, in our view, will consolidate Dolomedes as an ideal model lineage among spiders for addressing a vast array of questions across multiple fields of biology.

We report on a new species of Stenasellus Dollfus, 1897 (Isopoda, Stenasellidae) from groundwater of Iran. Stenasellus stygopersicus Jugovic, Malek-Hosseini & Issartel sp. nov. inhabits the Chah Kabootari Cave that is adjacent to the Tashan Cave, the type locality of the first recorded species of Stenasellidae from Iran, Stenasellus tashanicus Khalaji-Pirbalouty, Fatemi, Malek-Hosseini & Kuntner, 2018. Both caves are fed by sulfidic groundwater and belong to the Tashan-Chah Kabootari species-rich aquifer on the Zagros Mountains. Both species are characterized by a large body size (≥ 20 mm), a female-biased sexual size dimorphism, and a distinct black-pigmented Bellonci’s organ. Stenasellus stygopersicus differs from S. tashanicus by a short and wide protopodite of pleopod I, setae set essentially along the apical margin of pleopod I exopodite, the subequal length and width of the male pleopod II protopodite, and deeply bilobed endopodites of pleopods III–V. Molecular evidence suggests that while Stenasellus stygopersicus is sister to S. tashanicus, the species are genetically distinguishable, with divergence time estimates ranging from 23 to 39.8 Ma.

Sexual size dimorphism theory predicts biased operational sex ratios (OSRs) and an uneven distribution of males among certain females. We studied this phenomenon through a field census of the giant wood spider Nephila pilipes (family Nephilidae) in Singapore, a species where females are, on average, 6.9 times larger than males. Specifically, we tested two hypotheses concerning male distribution, given their tendency to aggregate in certain female webs. The optimal female size hypothesis predicts that males would predominantly occupy webs of intermediate-sized females. The web clustering hypothesis posits that more males would be found in webs closer together compared to those farther apart. Our snapshot census revealed a female-biased OSR (females: males = 1.85) with an uneven distribution of males in female webs. Most males were found in webs of intermediate-sized females aligning with the optimal female size hypothesis. Proximity among female webs was indicative of male presence, lending support to the web clustering hypothesis. While our study's limited sample size warrants caution, we conclude that in N. pilipes, male occupation of female webs is facilitated by the clustering of webs, and males prefer to cohabit with optimally sized, receptive females.

Predators often search for prey while moving through the environment, but there are important exceptions, including the way sedentary predators sometimes rely on signals for drawing prey to within striking distance1,2. Some spiders, for instance, leave the remnants of previously-captured prey in their webs where they function as static lures that effectively attract a diverse array of additional prey3456. However, important questions remain concerning how specific the targeted prey may be and how dynamic, instead of static, signalling might be. With these questions as our rationale, we initiated research on Araneus ventricosus (L. Koch, 1878), an orb-weaving spider, as the predator and the firefly Abscondita terminalis males as the prey (Figure 1A–C). Using two lanterns situated on their abdomen (Figure 1D,F), A. terminalis males make female-attracting multi-pulse flash trains (Figure 1J), whereas sedentary females attract males by making single-pulse signals (Figure 1C,K) with a single lantern (Figure 1E,G). Drawing from extensive field observations, we propose that A. ventricosus practices deceptive interspecific communication by first ensnaring firefly males in its web and then predisposing the entrapped male fireflies to broadcast bioluminescent signals that deviate from female-attracting signals typically made by A. terminalis males and instead mimic the male-attracting signals typically made by females. The outcome is that the entrapped male fireflies broadcast false signals that lure more male fireflies into the web.