Spiders are well known for using chemical, vibratory, tactile, and visual signals within mating contexts. All spiders produce silk, and even in non-web building spiders, silk is intimately tied to courtship and mating. Silk produced by females provides a transmission channel for male vibratory courtship signals, while webs and draglines provide a substrate for female sex pheromones. Observations of male spiders producing silk during sexual interactions are also common across phylogenetically widespread taxa. However, the function of male-produced silk in mating has received very little study. Exploring the function of male silk use during mating will provide a deeper understanding of the complex mating systems of spiders and allow tests of hypotheses about the evolution of male and female traits under sexual selection and/or conflict. In this review, we outline functional hypotheses that may explain each of the following three main categories of silk deposition males exhibit during courtship and mating: (1) silk deposition on females' webs or other silk structures, (2) silk deposition on females (‘bridal veils') and (3) silk associated with nuptial gifts. We then summarize the current knowledge of silk use by male spiders within these three categories and the types of mechanisms that may lead to functional effects, and discuss areas where future work can be targeted.

Allocosa senex (Mello-Leitão, 1945) is a sex role-reversed wolf spider that inhabits sandy water-margin environments of southern South America. Males are larger than females and dig deeper burrows. Females are the courting sex and they prefer to mate with males that build deep burrows, suggesting high selective pressures on male digging behavior. Our aim was to investigate the external morphology and histological constitution of the spinning apparatus of males, females and juveniles of A. senex. Our results showed that A. senex adult males possess more piriform glands and spigots than adult females and juveniles. These glands produce silk for attachment discs that are crucial for the stability of the burrows. The differences according to the sex could be related to females' and males' digging strategies and strong selection on male burrow length in this species.

Mygalomorphae spiders have several cuticular structures, such as stridulating, sensory and urticating setae, which offer great potential for phylogenetic studies. Spiders of the subfamily Theraphosinae have stridulating setae that aid in group taxonomy, having been found in numerous genera including: Acanthoscurria Ausserer, 1871, Aguapanela Perafán, Cifuentes & Estrada-Gomez, 2015, Citharacanthus Pocock, 1901, Cyrtopholis Simon, 1892, Grammostola Simon, 1892, Hemirrhagus Simon, 1903, Lasiodora C. L. Koch, 1850, Longilyra Gabriel, 2014, Pamphobeteus Pocock, 1901, Phormictopus Pocock, 1901 and Theraphosa Thorell, 1870. Some distinct bristle-like setae were examined using scanning electron microscopy with the following objectives: (1) to sample and describe the diversity of setae on the coxae and trochanters of representatives of the subfamily Theraphosinae; and (2) to code morphological characters useful for phylogenetics. We used a previously published phylogenetic matrix, with modifications to those characters that scored stridulatory setae, and analyzed these data using parsimony with implied weighting. Setae of the same type were found in Acanthoscurria, Brachypelma Simon, 1891, Cyrtopholis, Phormictopus and Theraphosa (claviform stridulating setae). A second type, which we name velvet stridulating setae, emerged as an autapomorphy of the genus Lasiodora, and spiniform stridulating setae were recovered as an autapomorphy of the genus Pamphobeteus. Some other setae similar to those of Lasiodora, named plumose stridulating setae, were found in Nhandu Lucas, 1983, Proshapalopus Mello-Leitão, 1923, Pterinopelma Pocock, 1901 and Vitalius Lucas, Silva & Bertani, 1993.

Arachnids have many setae that are used as sensory organs. Spiders have been shown to use trichobothria to sense air movements. Scorpions also have trichobothria, located solely on their pedipalps. In scorpions, these trichobothria have been used for taxonomic purposes, due to their systematic variations across taxa. In the lab, buthid scorpions respond to moth-like air vibrations by “hunting” a dummy prey, but scorpionids retreat. The eastern sand scorpion, Paruroctonus utahensis (Williams, 1968) is a member of the family Vaejovidae; by measuring its responses to air movements, we can begin to compare behavior of scorpion families. To determine the responses of P. utahensis to air stimulus, we created a piston-driven moth analog. To assess the trichobothria as candidate detectors of our air stimulus, we also monitored trichobothrial deflection in response to the moth analog. In behavioral trials, we ran this device for 10 seconds and recorded each scorpion's immediate responses as negative, neutral, or positive. For a control, we ran the device without its piston. Scorpions experienced both conditions. We found a significant difference between scorpions' responses under experimental and control conditions. On average, scorpions responded more negatively to experimental conditions as compared to control conditions. These data suggest that vaejovids, like scorpionids, retreat when they encounter a moth. We also found that our device was effective in stimulating appropriate trichobothrial deflection. Our moth analog could therefore be useful in further studies investigating the physiological mechanisms of prey detection.

Sperm competition influences the evolution of many reproductive traits such as gonads, sperm or genitalia. Many sperm competition analyses concentrate in testes and ejaculates. Among arachnids, scorpions constitute an intriguing taxon for examining sperm production and usage. For example, in the family Bothriuridae the females of Timogenes elegans Mello-Leitão, 1931 accept more than one male per reproductive season and males produce spermatozoa continuously, storing them inside two elastic storage organs (i.e., two seminal vesicles plus two deferent ducts) before inseminating females, using a sclerotized spermatophore. In this study, we analyzed the sperm storage organs and the ejaculate volume transferred by T. elegans. We described the volume and number of spermatozoa at storage sites and in ejaculates, and investigated ejaculate volume and concentration in remating experiences. Storage organs varied in total size. Inside the spermatophore, the volume of the sperm drop represented 38% of the volume of both sperm storage sites. The remaining space around the sperm drop is filled with a gel-like substance. The ejaculate volume and spermatozoa number did not vary significantly between consecutive matings. Timogenes elegans stored abundant sperm inside the seminal vesicles. Available sperm was divided equally between both storage organs, and ejaculates were diluted in the spermatophore, presumably, with the gel stored in the trunk. There was no effect of body condition over any of the variables analyzed. Male sperm storage and ejaculate production are discussed considering the sperm depletion hypothesis and the sperm competition theory.

Cave organisms are often relictual, ancient lineages that conserve characters no longer represented in their closest relatives. I here present a new species of Filistatidae from Mexican caves with a notable suite of characters that preclude its placement in any of the filistatid genera currently recorded from North America. A detailed study of its morphology using light and scanning electron microscopy indicates that this is the first mainland species of Antilloides Brescovit, Sánchez-Ruiz & Alayón, 2016 and I describe it as Antilloides chupacabras sp. nov. The genus was previously known only from the Antilles, and its presence in Mexico is evidence of a wider distribution. I here identify some characters which are novel putative synapomorphies of Antilloides, and the phylogenetic affinities of the genus are discussed. Finally, the presence of a modified metatarsus II in males of the new species, among other characters, suggests that the only known fossil filistatid, Misionella didicostae Penney, 2005 from Dominican amber, is misplaced in this genus and the new combination Antilloides didicostae comb. nov. is proposed.

The aganippine spiny trapdoor spiders of the genus Bungulla Rix, Main, Raven & Harvey are revised, and 30 new species are described from Western Australia: B. ajana sp. nov., B. aplini sp. nov., B. banksia sp. nov., B. bella sp. nov., B. bidgemia sp. nov., B. biota sp. nov., B. bringo sp. nov., B. burbidgei sp. nov., B. dipsodes sp. nov., B. disrupta sp. nov., B. ferraria sp. nov., B. fusca sp. nov., B. gibba sp. nov., B. hamelinensis sp. nov., B. harrisonae sp. nov., B. hillyerae sp. nov., B. inermis sp. nov., B. iota sp. nov., B. keigheryi sp. nov., B. keirani sp. nov., B. kendricki sp. nov., B. laevigata sp. nov., B. mckenziei sp. nov., B. oraria sp. nov., B. parva sp. nov., B. quobba sp. nov., B. sampeyae sp. nov., B. weld sp. nov., B. westi sp. nov. and B. yeni sp. nov. The type species, B. bertmaini Rix, Main, Raven & Harvey, 2017, is re-illustrated and re-diagnosed, and B. riparia (Main, 1957) is re-described. Molecular data from seven genes for a subset of taxa are analyzed with Bayesian methods, to complement the morphological descriptions, to help delimit three species known only from female specimens, and to generate a provisional phylogeny of the genus. Species of Bungulla exhibit a remarkable range of genitalic and somatic morphologies, and we here document this diversity, demonstrating that the characteristic loss of the retrolateral tibial apophysis has not been associated with a concomitant loss of genitalic complexity. We further provide a key to all known species and highlight the southern Carnarvon Basin (including the western Yalgoo and northern Geraldton Sandplains) as a hotspot of diversity.

Two new troglomorphic pseudoscorpion species, Bisetocreagris maomaotou sp. nov. (Family Neobisiidae) and Tyrannochthonius chixingi sp. nov. (Family Chthoniidae) are described from one cave in the tower karst of northern Guangxi Province, China. This cave is located at close proximity to a village and an adjacent urban area. As with many caves in the South China Karst, this feature occurs at an elevation slightly above agriculture and rural activities; thus, we suggest it may be partially buffered from human activities in the lowland areas. We discuss the likelihood of narrow range endemism and provide research and conservation recommendations to guide future management of these two species.

Gonyleptes curvipes Kollar, in C.L. Koch, 1839 has taxonomic problems: it is a primary junior homonym of Gonyleptes curvipes Guérin-Méneville, 1837; the holotype of G. curvipes Kollar was cited twice by Roewer (1913) under two genera, one being a misidentification of an undescribed species and a new combination under Discocyrtus Holmberg, 1878; Koch labeled another unreported specimen as Gonyleptes curvipes. However, this specimen belongs to a species described later by Roewer as D. crenulatus Roewer, 1913. In 2003, Kury transferred G. curvipes sensu Roewer to Discocyrtus and, to avoid homonymic collision with D. curvipes sensu Roewer, proposed the new name D. confusus as a replacement name. Discocyrtus confusus was later considered an invalid replacement name and was used to newly describe the species named by Kollar and Koch. Discocyrtus flavigranulatus B. Soares, 1944 is here considered a new junior subjective synonym of G. curvipes Kollar, but which is the next oldest available synonym. Discocyrtus confusus thus also becomes a junior synonym of D. flavigranulatus. Here we discuss the history and identity of three species of Discocyrtus: D. flavigranulatus B. Soares, 1944; D. crenulatus Roewer, 1913; and D. fenax sp. nov. from Santa Catarina state, Brazil (misidentified by Roewer as D. curvipes).

Vertical asymmetry is a widespread feature of orb webs, with the lower part larger than the upper, although its adaptive value is not fully understood. Gravity is thought to play a major role in the generation of asymmetry through increased running speed downwards from the hub. The relationship between spider orientation and gravity has been relatively well studied. However, webs' inclination from vertical has been less studied. Here we conducted a field study on the tetragnathid orb spider Metellina mengei Blackwall, 1869, which constructs webs that show a marked variation in inclination. Our findings revealed a significant influence of the degree of web inclination and web area on the level of vertical asymmetry, while environmental variables did not have any effect. Thus, our results support the hypothesis that the asymmetry in upwards and downwards running speeds due to gravity is an important determinant of web asymmetry.

Ecologists are often required to accurately estimate the number of individuals residing in groups of variable sizes inside opaque shelters. Here, we have used x-rays as a non-destructive solution to this problem in social spiders which reside within collectively built opaque, silken, nest-like retreats. Social spiders are model systems for understanding social organization, collective behaviours and population genetics of inbred populations. Such studies often require an accurate determination of the number of individuals, developmental stages and orientation of individuals within the colony which is difficult without compromising the integrity of their retreat or affecting colony behaviour. We demonstrate the effectiveness of x-rays in accurately estimating colony size in the social spider Stegodyphus sarasinorum Karsch, 1892 (Eresidae). This method can also be applied to evaluate body sizes, developmental stages and individual orientation within the colony. We show that this technique does not alter spider prey-capture behaviour or short-term survival compared to control colonies.

We analyzed effects of pitfall trap color on spider catches using four different pitfall trap colors (white, yellow, green, brown). For each color, we installed 17 pitfall traps at two grassland sites, respectively, and sampled 77 species from 6,202 individuals. Number of species showed no significant differences but Shannon- and Simpson-diversity were significantly higher in green and brown traps while number of individuals increased in white ones. Species inventories were not complete in the different pitfall trap colors but species accumulation increased significantly slower in white and brown traps. Trap color significantly affected hunting type with ground hunters being associated with bright and web-builders associated with dark colors. Attractiveness of different trap colors may arise due to differences in biological preconditions, albedo and microclimate which in turn can affect diversity and community structure of spiders. Trap color has a significant impact on spider catches and should be considered when planning surveys. We recommend the use of a combination of white and brown (or transparent) pitfall traps to gain complete and diverse species inventories in spiders.

Natural selection predicts that organisms should maximize reproductive fitness by exhibiting a tradeoff between the quantity and quality of offspring. While many species clearly show this tradeoff, it is not a ubiquitous phenomenon. Indeed, observing this tradeoff in different organisms is contingent on life history traits, reproductive strategy, parental investment, and physiological constraints. We tested for a tradeoff between the number and quality of offspring in the amblypygid Phrynus longipes (Pocock, 1894)—a long-lived, iteroparous arachnid with indeterminate growth, post-ultimate molts, and parental care. We measured the size of gravid females and the mass and number of eggs in their clutches. Egg count, but not mass, was predicted by female size, indicating that we did not detect an offspring quantity-quality tradeoff. We posit that larger female P. longipes are laying more eggs rather than increasing investment in each egg. This study is the first of its kind in any amblypygid species.

Camel spiders (Arachnida: Solifugae) are a notoriously difficult group of arachnids to study. They are almost all strictly nocturnal, fast moving predators that are difficult to find, collect, and rear. In this paper, we present methods for both attracting solifuges in desert field sites and collecting them efficiently using a combination of light attraction and pitfall trapping techniques. Although many of these methods have been used by solifuge collectors for decades, they are not typically described in detail in the literature nor have the methods been consolidated in a single paper. We hope that doing so will enable others to more efficiently target this group of arachnids.