Journal of Arachnology

List of all articles

Volume 50 Number 2

Abstract

The spider Myrmecicultor chihuahuensis Ramírez, Grismado & Ubick (Myrmecicultoridae) was described in 2019 and hypothesized to be a myrmecophile, living inside the nests of Novomessor (Myrmicinae) and perhaps also Pogonomyrmex (Myrmicinae) ants. To test the hypothesis that M. chihuahuensis are chemical mimics of their host ants, we carried out behavioral bioassays to observe interactions between the spiders and the host ants. We compared the cuticular hydrocarbon (CHC) profiles of the spiders and the ants. We discovered that this new species of spider is a myrmecophage, displaying hunting strategies similar to other myrmecophagous spiders, particularly those in the genus Zodarion Walckenaer, 1826 (Zodariidae). The CHC profile of M. chihuahuensis did not match the profile of the ants with which it associates, Novomessor albisetosus (Mayr), but ants and spider shared several compounds, potentially involved in species recognition.

Volume 50 Number 2

Abstract

Sociality in spiders has evolved independently multiple times, resulting in convergently evolved cooperative breeding and prey capture. In all social spiders, prey is captured by only a subset of group members and then shared with other, non-attacking group members. However, spiders' propensity to attack prey may differ among species due to species-specific trade-offs between risks, costs and benefits of prey capture involvement. We explored whether engagement in prey attack differs among three social Stegodyphus species, using orthopteran prey, and found substantial differences. Stegodyphus mimosarum Pavesi, 1883 had a low prey acceptance rate, was slow to attack prey, and engaged very few spiders in prey attack. In S. sarasinorum Karsch, 1892, prey acceptance was high, independently of prey size, but more spiders attacked when prey was small. While medium-sized prey had higher acceptance rate in S. dumicola Pocock, 1898, indicating a preference, the number of attackers was not affected by prey size. Our results suggest that the three species may have different cooperative prey capture strategies. In S. mimosarum and S. dumicola, whose geographical ranges overlap, these strategies may represent niche specialization, depending on whether their respective cautious and choosy approaches extend to other prey types than orthopterans, while S. sarasinorum may have a more opportunistic approach. We discuss factors that can affect social spiders' foraging strategy, such as prey availability, predation pressure, and efficiency of the communal web to ensnare prey. Future studies are required to investigate to which extent species-specific cooperative foraging strategies are shaped by ontogeny, group size, and plastic responses to environmental factors.

Volume 50 Number 2

Volume 50 Number 1

Volume 50 Number 1

Abstract

In this work we describe Ctenus igatu sp. nov., the first ctenid spider from South America with conspicuous troglomorphic traits, including elongated appendages, reduction of eyes, and body depigmentation. The new species is only known to occur in a unique sandstone cave from the state of Bahia, north-eastern Brazil. The morphology of the genitalia suggests that Ctenus igatu sp. nov. is closely related to Ctenus fasciatus Mello-Leitão, 1943, a facultative subterranean species from caves in the state of São Paulo, south-eastern Brazil. In addition, we compared morphological traits possibly related to the isolation in subterranean habitats, such as ratios between carapace length vs. leg IV length and eye diameters vs. carapace length, of 19 species of Ctenus (17 epigean species, C. fasciatus and the new troglobitic species described herein). Our analysis showed that both C. fasciatus as C. igatu sp. nov. have morphological troglomorphisms, with C. igatu sp. nov. showing marked specializations to subterranean life.

Volume 50 Number 1

Abstract

The Araneidae is among the most speciose spider families, but there are few karyotype studies (1.9%) and some species-rich clades are without any chromosomal study. Understanding the evolution of chromosome number and Sex Chromosome Systems is made more difficult by many uncertain evolutionary relationships within the family. In this work, the chromosomal analysis of eight araneid species (Acacesia benigna Glueck, 1994, Actinosoma pentacanthum (Walckenaer, 1841), Alpaida bicornuta (Taczanowski, 1878), Dubiepeira Levi, 1991 sp., Gasteracantha cancriformis (Linnaeus, 1758), Parawixia bistriata (Rengger, 1836), Verrucosa meridionalis (Keyserling, 1892) and Verrucosa scapofracta Lise, Kesster & Silva, 2015), contribute to discussions of some evolutionary scenarios of chromosome evolution. The gonads were submitted to colchicine treatment, hypotonization, slide preparation, and Giemsa staining. The species analyzed showed 2n♂ = 24 (11II + X1X2), except Dubiepeira sp. with 2n♂ = 41 (19II + X1X2X3), and both Verrucosa species, which presented 2n♂ = 47 (22II + X1X2X3) in V. meridionalis and 2n♂ = 50 (23II + X1X2X3X4) in V. scapofracta. The species analyzed possess all chromosomes with acro/telocentric chromosomal morphology. The 2n♂ = 24, X1X2 found in most species studied here is the most frequent karyotype in the Araneidae. This study presents the first chromosomal data for the diverse clade “Micrathenines”, the highest diploid number among entelegynes (2n♂ = 50), and the first record of an X1X2X3X4 in the Araneidae. The chromosome data suggest a series of fission events in the origin of Verrucosa karyotypes, and a close relationship between Dubiepeira sp. and Araneus ventricosus (L. Koch, 1878). Moreover, Alpaida bicornuta can be cytotaxonomically distinguished of other Alpaida species karyotyped up to now.

Volume 50 Number 1

Abstract

We studied dispersal of brown recluse spiders, Loxosceles reclusa (Gertsch & Mulaik, 1940), around an infested urban garage using pitfall traps. Over a four-month period, 23 were captured from a source population that averaged 100 individuals observed in nocturnal censuses. Loxosceles reclusa were captured in far lower proportions compared to their potential source population size than were other spiders such as theridiids and agelenids that also resided in the garage, albeit in far lower numbers. Dispersal was weakly positively correlated with the source population size. We compare our findings to anecdotal reports from prior studies and the general consensus that brown recluse spiders are poor dispersers to argue for more detailed examination of the movement and specific habitat requirements of this medically important spider. Habitat specificity and high mortality during dispersal may help explain the highly clustered spatial distribution of brown recluse spiders, not only a lack of attempted emigration.

Volume 50 Number 1

Abstract

Parthenogenesis and sex-ratio bias may lead to erroneous assumptions concerning the natural history of some arachnids. To help address this issue, this study provides new data on the sex ratio and geographic distribution of sexual populations of the scorpion Tityus stigmurus (Thorell, 1876). Ultraviolet light lanterns were used to detect specimens during nocturnal searches performed in both urban and non-urban environments scattered thorough northeastern Brazil. Males of T. stigmurus were reported for 10 new localities, and although we did not find males in urban environments, non-urban populations presented near symmetrical sex ratios. Such results suggest that reproductive strategies in this species may be modulated by environmental conditions. Also, the general tendency of less biased sex ratios in non-urban environments reported here is in accordance with previous studies that indicated the occurrence of geographical parthenogenesis in this species. Thereby, we propose that sexual populations of T. stigmurus are less rare than previously reported.

Volume 50 Number 1

Abstract

Online open databases are increasing in number, usefulness, and ease of use. There are currently two main global databases for spiders, the World Spider Catalogue (WSC) and the World Spider Trait (WST) database. Both are regularly used by thousands of researchers. Computational tools that allow effective processing of large data are now part of the workflow of any researcher and R is becoming a de facto standard for data manipulation, analysis, and presentation. Here we present an R package, arakno, that allows interface with the two databases. Implemented tools include checking species names against nomenclature of the WSC, obtaining and mapping data on distribution of species from both the WST and the Global Biodiversity Information Facility (GBIF), and downloading trait data from the WST. A set of tools are also provided to prepare data for further statistical analysis.

Volume 50 Number 1

Abstract

In this paper, we present an update on our knowledge on egg predation (oophagy) by spiders. Based on a survey of 233 reports, ghost spiders (Anyphaenidae), lynx spiders (Oxyopidae), jumping spiders (Salticidae), and yellow sac spiders (Cheiracanthiidae) were the most prominent groups of spiders engaged in oophagy. Around 75% of the reports referred to the consumption of lepidopteran and spider eggs worldwide. Another 10% referred to the consumption of eggs/embryos of anurans – especially predation upon embryos of glass frogs (Centrolenidae) by spiders from the families Anyphaenidae and Trechaleidae in the Neotropics. The remaining 17% included rare instances of feeding on eggs of coleopterans, dermapterans, dipterans, heteropterans, homopterans, hymenopterans, acarids, neuropterans, opilionids, and squamates. Our study demonstrates that oophagy in spiders is much more widespread than previously thought, both geographically and taxonomically. The finding that spiders feed on eggs/embryos from so many different invertebrate and vertebrate taxa is novel.

Volume 50 Number 1

Abstract

Pseudoscorpions are known worldwide and yet are poorly studied mainly due to the difficulty of detecting them. Among their predators are ground-dwelling taxa, such as arthropods, amphibians, birds, and reptiles. Only four pseudoscorpion species are known to occur in the Cabo Verde Archipelago, and none in the Desertas Islands, located in the northwest of the country. In this study, we record the first two species for the Desertas Islands. We used molecular and morphological methods to taxonomically identify the specimens retrieved from reptile faecal pellets and pitfall traps. We identified the presence of Garypus cf. saxicola on Raso Islet, Olpium pallipes (Lucas, 1849) on Raso and Santa Luzia Island, and a putative new species of Olpium L. Koch, 1873 on Branco Islet. This study emphasizes how an indirect measure of biodiversity and ecological interactions via potential predators, using non-invasive sampling combined with metabarcoding and morphological studies, can be used to uncover unknown biodiversity, particularly of cryptic groups from highly inaccessible locations. Likewise, this study highlights the lack of 16S genetic resources for pseudoscorpions in online reference databases.

Volume 50 Number 1

Abstract

The pholcid spiders Modisimus bribri Huber, 1998 and M. guatuso Huber, 1998 construct three-dimensional webs, including sheet dome and irregular shapes, occasionally shared by males and females. We studied species spatial disaggregation and confirmed web-sharing and prey capture dominance in shared webs. We observed 22 M. bribri and 25 M. guatuso webs and recorded their height above the ground, dome dimensions, and web-sharing. In shared webs, we recorded which individual captured prey. Modisimus bribri builds webs at greater heights (∼6.5 times), with larger dimensions (∼2 times) than M. guatuso. In both species, neither the occupant sex nor the number of individuals on the web had a significant effect on web dimensions. We confirmed differential web location between species and did not find evidence of chivalrous dominance in prey-capture in shared webs. This study contributes to the general knowledge of three-dimensional web-building spiders, posing new questions for future research.

Volume 50 Number 1

Abstract

Many animals, including many arachnids, return to an established “home” after an active period. Although desert-adapted solifuges shelter from the sun in retreats, it is unknown if these solifuges “home” to and re-use the same retreats over multiple consecutive periods. We sought to investigate whether individual solifuges exhibit site fidelity (philopatry) and could be found repeatedly within the same small geographic area using a simple mark-and-recapture study design. Over the course of the seven-day study period, nine of 46 solifuges were recaptured once, and two were recaptured a second time, with an average of 4.17 m between encounters. This rate of recapture is suggestive that solifuges remain in or return to the same geographic area over some period of time – a prerequisite for homing behavior. Further investigation is warranted to establish if solifuges are repeatedly using the same retreats, and if so, how they are navigating during homing.

Volume 50 Number 1

Abstract

The ichneumonid parasitoid Sinarachna nigricornis (Holmgren, 1860) was associated only with Araneus sturmi (Hahn, 1831) in the studied locality. The normal capturing orb web of A. sturmi was always vertical and had a median of 18 radii and 9 spirals in laboratory conditions. When spiders did not build capture webs, they built resting and molting webs which consisted of a few threads between the ends of the provided tree twigs. There were no significant differences in the number of radials and spirals between unparasitized spiders and spiders parasitized by early instar parasitoid larvae. Araneus sturmi under manipulation by S. nigricornis built a modified cocoon web, serving parasitoid larva pupation. S. nigricornis exhibited high plasticity in the architecture of the cocoon web induced by its penultimate instar larva. The most common cocoon web was of 3D architecture with a small central silk platform, from which the wasp cocoon was suspended by its apical end (72% of webs). In 22% of cases, the cocoon web consisted only of a few threads, presumably resembling a molting web. In one case, the manipulated spider built a 3D tangle, though radials and the central hub (typical for the normal capturing web) were also present. The genus specificity of the cocoon web architecture described here, in which the typical cocoon web exhibits a sparse but strong 3D architecture and in which the wasp cocoon is suspended by its apical end at the center, is expected for the genus Sinarachna.

Volume 50 Number 1

Abstract

Sexual cannibalism is common in many species of arachnids. Studies investigating Dolomedes tenebrosus Hentz, 1844, have even discovered the occurrence of obligatory male self-sacrifice during copulation. In this system, females subsequently cannibalize males, and this cannibalism leads to higher fitness for both partners. Unfortunately, our understanding of the evolution of such an extreme mating system is challenged by the absence of information for close relatives. To that end, this study explores the courtship behavior, mating system and cannibalism dynamics of the spider Dolomedes scriptus Hentz, 1845. To determine whether female and male D. scriptus mate multiply, we recorded interactions of repeatedly exposed focal females and focal males to new mating partners for three days. We also quantified attacks and cannibalism events that occurred both before and after every copulation. We found male D. scriptus court females by waving their forelegs during their approach and tapping the females prior to mounting. In our remating trials, none of the female D. scriptus accepted additional males after their first mating over the three-day period. In contrast, male D. scriptus were polygynous, often mating with multiple females. Across the trials, sexual size dimorphism was a predictor of whether mating occurred, with similarly sized pairs being more likely to mate. Additionally, previously mated females were less likely to cannibalize males—an unusual pattern for spiders. Like other species of Dolomedes Latreille, 1804, our results suggest a strong role of female aggression in D. scriptus mating system dynamics.

Volume 50 Number 1

Abstract

Species recognition and reproductive isolation are critical for organisms to prevent expensive and unsuccessful matings. This may be particularly important in closely related species that coexist synchronously in the same habitat, and for which reproductive barriers are not entirely effective. Tetragnatha argentinensis Mello-Leitão, 1931 and T. nitens (Audouin, 1826) are two long-jawed orb weaver spiders whose feeding grounds and reproductive phenology overlap extensively. Since general patterns of sexual behavior observed in the field showed no apparent differences between these two species, we proposed to evaluate the occurrence of heterospecific mating, and explored the occurrence of potential reproductive isolation mechanisms between them by analyzing in fine scale the mating behaviors of each species and sex. We observed only one heterospecific mating, and few or no sexual interactions occurred in other crossed trials. We found that both species showed similar general mating patterns, however, there are some subtle differences between them. In T. nitens, males clasped the female's chelicerae with their own, but the opposite occurred in T. argentinensis. Moreover, males of T. nitens produced fewer hematodochal inflations, lower number of flubs, and shorter insertions than males of T. argentinensis. Females of T. argentinensis vibrated their abdomen at a higher rate. Our results indicate that these sympatric Tetragnatha species have successful reproductive isolation that probably takes place through recognition mechanisms occurring prior to mating. We provide an update on the taxonomic status of T. argentinensis and its distribution, and a new junior synonymy.

Volume 50 Number 1

Abstract

There are few works on the reproductive behavior of species of cribellate spiders. Even more scarce are studies of the reproductive behavior of representatives of the Desidae, such as the genus Metaltella Mello-Leitão, 1931. In this paper, we describe for the first time the reproductive behavior of Metaltella iheringi (Keyserling, 1891), a species that is characterized by complex genitalia in both sexes. We determined frequencies and durations of the behaviors in the different phases. Thirty virgin males were exposed to virgin females and the behaviors performed by each sex, as well as their frequencies, were recorded. Three phases were identified: pre-copulatory, copulatory, and post-copulatory. The most frequent behaviors were chelicera-palp rubbing, abdomen vibration and web-stretching by the male, and body-shaking and leg-tapping on the web by the female. When the male grabbed the female, she typically fell into a state of quiescence (the female remained motionless with legs in a semi-flexed position) and she remained so even after the male ended the copulation. Mating was characterized by low aggression by the female and a low incidence of cannibalism. In the post-copulatory phase, the male performed frequent behaviors such as abdomen vibration, sperm induction, and post-copulatory cohabitation. We discuss the possible implications of these behaviors in a pre- and post-copulatory sexual selection context. We also provide information that serves as a basis for future studies to understand the mechanisms involved in these behaviors.

Volume 50 Number 1

Abstract

Microhabitat use by predators can be influenced by prey availability, predator size and risk of cannibalism. The preferred microhabitat for a predator can be for foraging, feeding or as a refuge. In this study in south Texas, Centruroides vittatus (Say, 1821) of all size classes utilized both ground and vegetation microhabitats. There was a high proportion of scorpions with caterpillars in legumes and low proportion of scorpions with any of the prey types on the ground. The median height of scorpions with prey did vary, with scorpions on legumes with caterpillar prey the highest and scorpions on other vegetation with dangerous prey the lowest. Intermediate size scorpions used legumes at a high frequency during January–April, and large scorpions used succulents at very high frequency during September–December. Scorpions climbed higher in blackbrush and other legumes than in other vegetation types. These results suggest that scorpions are actively foraging for caterpillars in legumes, and legumes are a quality microhabitat for foraging. The low proportion of scorpions with prey on the ground suggests that C. vittatus feed on prey on vegetation even if the prey was captured on the ground. A possible advantage for the scorpion to handle and consume prey on vegetation is lower predation risk or interference while feeding. The high use of succulents by the large scorpions cannot be explained by foraging success. A possibility is that succulents are preferred refuges by all C. vittatus but smaller scorpions avoid succulents because of the risk of cannibalism by the larger scorpions.

Volume 50 Number 1

Abstract

The troglobitic harvestman Jimeneziella decui Avram, 1970 is known from four neighboring caves (Cueva de Majana, Cueva de los Golondrinos, Cueva Perla del Agua, and Cueva de Máximo) located in eastern Cuba. We present the first ecological data on a population of this endangered species in Cueva de Máximo. The sex ratio of the population estimated in the main gallery of the cave was not different from 1:1. The spatial distribution observed was uniform, and the density of individuals was 0.48 individuals/m2 (February–March) and 0.84 individuals/m2 (November). We describe morphological differences between the sexes and between males. Preliminary morphological and behavioral data suggests the possible existence of two male morphs in J. decui (“robust” and “slender” males). The slender males possessed less developed armature on leg IV; and the chelicerae, coxa IV and femur IV were less swollen than robust males. Our observations on male-male interactions suggest that robust males are more aggressive than slender males, which never initiated an attack on robust males, but in some occasions responded to attacks from robust males. The non-aggressive behavior exhibited by robust males towards slender males also suggests that the slender morph is not only a sneaker, but potentially a female mimic, which is also consistent with the morphology of slender males. Ecological and behavioral information also suggests the possible existence of territories defended by robust males with their well-developed weapons, and the presence of females inside them.

Volume 50 Number 1

Abstract

The World Arachnida Catalog (WAC, online at https://wac.nmbe.ch) is introduced as an amalgamation of the highly successful World Spider Catalog (WSC), the Pseudoscorpions of the World Catalog, and the Smaller Arachnid Order Catalogs. The new catalogs present all available taxonomic information on eight arachnid orders (Amblypygi, Araneae, Pseudoscorpiones, Ricinulei, Palpigradi, Schizomida, Solifugae and Uropygi) in a single location and a standardized format, continuously updated by specialists, to members of the World Spider Catalog Association (WSCA). For the first time, the majority of taxonomic literature for Pseudoscorpiones and the smaller arachnid orders will be available in downloadable PDF format for members according to the Swiss copyright laws. Up-to-date counts of families, genera and species are given alongside the current taxonomy for each taxon. Now in a common place and presented in an almost unified format, the new catalog aims to become the primary repository of taxonomic information for the Arachnida and will hopefully stimulate arachnological research across all arachnid orders by removing boundaries imposed by literature accessibility, incompatibility of formats, or taxonomic jargon.

Volume 49 Number 3

Volume 49 Number 3

Abstract

Parasites are some of the most abundant, diverse, and ecologically important organisms on the planet. Similarly, spiders are diverse, abundant, and play important roles in many terrestrial ecosystems. It is unfortunate that our understanding of the parasites that affect spiders is so underdeveloped relative to similar fields (e.g., parasites of insects). With this review, we describe characteristics of the major groups known to parasitize spiders and illustrate the ways in which spider biology presents unique challenges and opportunities for their parasites. Particularly promising avenues of future research include testing how parasites alter their spider hosts’ behavior and ecology through density-dependent and trait-mediated effects. We close by providing future directions and testable hypotheses at the forefront of spider-parasite research.

Volume 49 Number 3

Abstract

The exploration of new and diverse animal groups in the study of sexual selection is both necessary and important to help better understand broad patterns and test sexual selection hypotheses regarding the evolutionary origins and maintenance of reproductive tactics and associated traits. Solifuges are, in this matter, an exceptional group and very little explored from the sexual selection point of view. At first glance, mating is apparently quite simple and conserved within this arachnid order, but solifuge reproductive behavior is unique among arachnids and more diverse than previously thought. In particular, these voracious animals appear to exhibit high sexual conflict, as males need to avoid being eaten by their aggressive female partners and mating encounters in some species involve periods of apparently male-induced female inactivity during sperm transfer. The extent to which reproductive encounters are coercive versus collaborative, however, remains largely unknown. In this review, we begin with a historical perspective of sexual behavior research in solifuges. We then discuss precopulatory mating patterns, the role of the female and male during mating, sexual dimorphism, and the influence of sexual selection during different stages of mating. In addition, we explore cases of sexual cannibalism and provide an updated analysis of how postcopulatory sexual selection may be acting on these amazing arachnids. This review shows that there is much to be done in this extraordinary group of animals.

Volume 49 Number 3

Abstract

The design of orb webs is affected by multiple abiotic (e.g., wind, available space), biotic (e.g., prey availability, predation), and species specific (e.g., spider size) factors. Thus, some features of each spider web are expected to reflect the combined effect of such factors. We compared the relationship of spider size and web inclination on the area of different sections of the orb web and other features (e.g., number or radii) between two sympatric Leucauge species (Leucauge sp., and L. argyra (Walckenaer, 1841), Tetragnathidae). Leucauge sp. was smaller and constructed smaller webs across a wider range of inclinations than L. argyra. Other features of the web, e.g., capture area, and hub area, but not the number of adhesive spiral turns and number of radii, were also larger in webs of L. argyra. The inclination was greater in webs of Leucauge sp., but the asymmetry of webs did not differ between species, though, it correlated negatively with the total area of the web of both species, as in other orb-weavers. The characteristics of each species’ web suggest that L. argyra optimizes prey interception, while Leucauge sp. optimizes stopping and retention of large prey.

Volume 49 Number 3

Abstract

A key challenge for generalist predators is avoiding toxins in prey. Species-specific strategies range from total avoidance of distasteful (and potentially toxic) prey to the use of physiological mechanisms to metabolize toxins after consumption. We compare two species of jumping spiders, Habronattus trimaculatus Bryant, 1945 and Phidippus regius CL Koch, 1846. Based on several anecdotal observations and other aspects of their biology, we hypothesized a priori that H. trimaculatus would be (1) less willing to feed on unpalatable prey and (2) more susceptible to toxins that are consumed compared with P. regius. In Experiment 1, we presented spiders of both species with size-matched quinine-dipped crickets. Consistent with our hypothesis, all H. trimaculatus attacked and rejected them while all P. regius attacked and consumed them. In Experiments 2 and 3, we assigned spiders of both species to experimental feeding treatments with varying levels of toxicity (using toxic springtails, Folsomia candida) and assessed effects on their growth. Spiders of both species readily fed on the springtails. Collectively, results from these two experiments suggest that springtails have negative effects on both species, but that these effects are stronger in H. trimaculatus. Habronattus FO Pickard-Cambridge, 1901 has a unique red retinal filter pigment (not found in Phidippus CL Koch, 1846) that likely improves their ability to discriminate reds and oranges. The evolution of this unique visual system may have been driven by their heightened susceptibility to prey toxins, and thus the benefits of avoiding prey that advertise toxins with long-wavelength colors.