Molecular genetic tools have been a boon to arachnologists for decades and used to study many unique aspects of arachnid biology including genomics, phylogenetics, population genetics, and biogeography. These tools have evolved over time and now provide myriad methods for exploring evolutionary questions. Early tools, while still useful under the proper circumstances, are giving way to a new generation of DNA sequencing technologies. These new platforms yield impressive amounts of data at a fraction of the cost of traditional techniques. Herein, we discuss the history and future of molecular evolutionary arachnology in terms of available genetic/genomic tools and their potential applications, strengths, weaknesses, and relative costs. Next-generation sequencing (NGS) platforms are varied in their methods and potential uses, making high-throughput sequencing studies focusing on a wide array of questions tractable. To date, relatively few studies have employed NGS technologies using arachnids, but many could benefit from using them. Because no model species exist within the class Arachnida, we have a limited understanding of arachnid genomics. With the ever-advancing nature of sequencing technologies and bioinformatics, arachnologists can relatively easily implement NGS studies to bridge the gaps in our understanding and open avenues for deeper and more powerful experiments. To this end, we discuss examples of applications of NGS technologies focusing on arachnid taxa. Despite the allure of acquiring massive quantities of sequence data, we should recognize the limitations of existing NGS technologies and not forsake pre-NGS methods when these technologies could adequately address our questions.

Two specimens of a new spider from the Cretaceous (ca. 129 Ma) El Montsec Fossil-Lagerstätte, northeastern Spain, are described as Montsecarachne amicus gen. et sp. nov. and referred to the extant haplogyne family Plectreuridae. Plectreurids are found today in only in the southwestern USA, Mexico, Central America and Cuba, but fossils show a more widespread distribution in Eurasia. The new species adds an additional stratigraphic and biogeographical record. The paleobiogeographical history of plectreurids is discussed, and it is concluded that the most likely scenario is that the family was more widespread in the past, and has suffered extinction over much of its range, resulting in the present distribution. Possibly, extant plectreurids represent a living remnant of a more diverse group of haplogynes that were widespread in the Mesozoic.

Spiders exhibit a remarkable variety of reproductive phenotypes such as induced parthenogenesis and reproductive skew in primary sex ratio. However, observations of distorted sex ratios are mainly inferred from field catches of adult individuals, whereas detailed information on clutch primary sex ratio and sex ratio inheritance, resulting from multiple generations of laboratory rearing, is scarce. One of the potential causes of sex ratio variation is infection with maternally inherited endosymbiont bacteria that alter a mother's offspring sex ratio to increase their own fitness. Although studies show that spiders are infected with several endosymbiont species, it was only recently discovered that endosymbiont bacteria can cause a female sex ratio bias in this order. To explore the distribution of biased sex ratios and endosymbiont infection patterns, we investigated sex ratio variation and bacterial presence in Oedothorax retusus Westring 1851. Significant sex ratio variation was detected in six matrilines originating from wild-caught females, one of which consistently showed a female bias in offspring production. Congruent with a bacterial effect, the sex ratio bias showed a clear maternal inheritance, and treatment with antibiotics reversed the sex ratio to equal numbers of males and females. Female-biased clutches were found to exhibit a significantly lower number of hatched spiderlings than unbiased clutches, suggesting the occurrence of male-killing. All matrilines showed infection with the Cardinium endosymbiont, while two matrilines, including the female biased one, were additionally infected with Wolbachia and Rickettsia. These findings indicate that bacterial endosymbionts are responsible for the sex ratio variation in this species, and suggest that effects of endosymbiont bacteria in the order Araneae could be more widespread than previously assumed.

We compared the structure of spider assemblages between the upper and lower canopy layers, and between the canopy and forest floor, in plantations of evergreen cedar (Cryptomeria japonica) and deciduous larch (Larix kaempferi). The estimated number of species was similar between the upper and lower canopy layers (49.0 vs 45.1) in C. japonica, but was noticeably smaller in the upper canopy layer (11.3) than in the lower layer (36.9) in L. kaempferi. Arboreal spider assemblages in the canopy differed significantly between the upper and lower layers in both C. japonica and L. kaempferi stands, based on an abundance-based measure. However, based on an incidence-based measure, they only differed significantly between layers in the L. kaempferi stand. The spider assemblages also differed distinctly between the canopy and the forest floor in both stands. Wandering spiders and orb-web builders were dominant in the canopy, while space-web builders dominated the forest floor in the C. japonica stand. In the L. kaempferi stand, wandering spiders dominated both the canopy and the forest floor. Our results suggested that spider assemblages in conifer plantations were distinctive among strata because of differences in such factors as resource quality (i.e., living or dead foliage) and association with adjacent layers along the vertical gradient of the forests.

The design of sampling schemes affects the results of biodiversity inventories. As an approach for quantifying the implications of such effects, we compared data on spider communities sampled in a beech-dominated forest floor habitat by 1) a regular grid of pitfall traps (systematic design) and 2) an expert-based distribution of traps (stratified design). We tested whether the two designs would lead to similar conclusions about the diversity and composition of ground-dwelling spider communities. Estimates of species richness, rarefied species richness and activity density calculated per trap were significantly higher in the stratified than in the systematic design. The community composition based on the presence or absence of sampled species or based on log-transformed activity densities differed significantly. Most of the dissimilarity between the community estimates of the two designs was attributable to three species, with Pardosa saltans Töpfer-Hofmann 2000 being more common in traps of the stratified design and Tenuiphantes zimmermanni (Bertkau 1890) and Walckenaeria cuspidata Blackwall 1833 being more frequently observed in traps of the systematic design. Our study suggests that a stratified sampling design is better suited for inventory surveys of spider communities of forest-floor habitats, as trap locations of this design reflect specific habitat needs. It is important to note that inventories are a major field for the application of such designs and that greater care is needed for the application of inferential statistics. For example, the non-randomness that is caused by expert selection of sampling sites may violate fundamental assumptions of simple linear models.

In many tropical areas of the world, pristine forests have become rare. Nevertheless, due to shifts in the human population the area covered by secondary forests is increasing. These forests may harbor a rich flora and fauna and are considered to be main refuges for species of primary forests. However, this issue is far from clear. To assess the conservation value of secondary forests in the Atlantic Forest of Brazil, we compared the diversity of spiders in differently aged secondary forests with old-growth forests. Within a larger project treating several invertebrate taxa, we sampled spiders using a standard protocol in 24 sites of three successional stages (5–8, 15–20, 30–50 years old) and old-growth forests (> 100 years untouched) in two nature reserves. We describe the diversity and structure of the assemblages using morphospecies and genera and analyze richness at the genus level. Generic richness and diversity showed no differences between successional stages; i.e., did not increase from the youngest to older forests, but guild diversity did increase. The youngest stage showed the highest variability in generic composition, and the turnover of genera and species was strong between the younger forests (5–20 years old) and forests older than 30 years. High alpha diversity, high turnover among sites and the lack of differences in richness between stages support the value of secondary forests for species conservation in the region studied.

Triaeris stenaspis Simon 1891 is a parthenogenetic goblin spider that has been introduced into greenhouses all over Europe. Here we investigated its trophic niche and predatory behavior. Potential prey in the greenhouses included predominantly springtails, aphids, and other spiders. Out of ten potential prey types offered in the laboratory, T. stenapsis captured only three types, the primary one being springtails. The spider rarely caught the other two types, termites and crickets, and completely rejected beetles, ants, aphids, thrips, flies, spiders and mites. Triaeris stenaspis did not build webs for prey capture, but instead used the grasp-and-hold tactic. Prey-capture efficiency decreased with springtail body size, the spider using more than three bites to capture large springtails. Large springtails defended themselves by saltation with the spiders still attached to their backs. Our study supports the hypothesis that T. stenaspis is a specialized predator of springtails, being effective in the capture of this type of prey.

Understanding when and how animals use their performance capacities can yield insights into the selection pressures driving high performance. Using two species of cursorial spiders, Schizocosa ocreata (Hentz 1844) and Rabidosa rabida (Walckenaer 1837) (Araneae: Lycosidae), we investigated the escape speeds exhibited by individuals of various body sizes in response to three aversive stimuli (jets of air, seismic cue, prodding) to determine how individuals use their performance capacity in response to different stimuli. We found that large individuals of both species exhibited their highest observed escape speeds in response to jets of air, whereas smaller individuals exhibited their fastest observed escape performances in response to prodding. We hypothesized that differences in escape behavior may reflect differences in risk associated with each cue type: fast moving jets of air may announce the arrival of an avian predator, and large individuals may be at greater risk of avian predation owing to their more conspicuous body size; whereas smaller individuals may be more susceptible to arthropod predators, which attack from the level of the spider, similar to a prod. We then performed an unreplicated mark-recapture, avian-exclosure experiment for both species, where we tracked individuals' persistence for 30 d. Consistent with our predictions, we found that larger individuals enjoyed greater persistence in our avian exclosure treatment, but their advantage was lost when avian predators were allowed to enter. Our results suggest that these spiders express their highest performances in only their most dire situations.

The taxonomy of the cheliferid pseudoscorpion genus Chelifer Geoffroy 1762 is reviewed with a single cosmopolitan species, Chelifer cancroides (Linnaeus 1758), with the subspecies C. cancroides orientalis Morikawa 1954 from Japan newly synonymised with C. cancroides. Adults and the final two nymphal stages (tritonymph and deutonymph) are redescribed based on numerous specimens from Europe, North America, Asia and Australasia. The large size variation evident in the samples is documented. The latero-ventral process of the tarsal claws characteristically found in adults (except leg I of the male) is lacking in nymphs, a pattern that is also confirmed in the genera Lissochelifer Chamberlin 1932, Lophochernes Simon 1878 and Parachelifer Chamberlin 1932.

The first blind African species of Ideoroncidae is described from a cave in northwestern Botswana, Botswanoncus ellisi, representing a new genus and a new species. Apart from the complete lack of eyes, it is also unusual in having the lowest recorded number of trichobothria of any adult ideoroncid with 17 on the fixed finger and nine on the movable finger.

Scorpions are nocturnal arachnids that fluoresce a bright cyan-green when exposed to UV light. Although the function of this fluorescence remains unknown, some authors have suggested that it may aid the scorpions' light detection. Taking advantage of scorpions' negatively phototactic behavior, we tested the responses of desert grassland scorpions, Paruroctonus utahensis (Williams 1968), to 395 nm UV light at irradiances corresponding to an hour before sunset (0.15 µW/cm²), sunset (0.01 µW/cm²), and moonlight (0.0001 µW/cm²), as well as no light. We found that animals showed the strongest responses to UV light levels equivalent to sunset. The animals moved more quickly and sporadically under the higher light levels. In addition, animals were less likely to complete a trial under highest light conditions, suggesting that UV light may inhibit normal scorpion locomotion. Finally, this study resulted in several methodological refinements, including automated tracking of the subjects' movements that should prove useful in future behavioral studies of scorpion phototactic behavior.

A scorpion's last metasomal segment (telson) consists of a bulbous base that contains two venom glands and a curved tip (aculeus) where two venom ducts open to the outside. These two openings lie laterally just before the very tip of the aculeus; to see both of them at the same time, the stinger has to be looked at “tail-on” from the dorsal side. The two venom ducts have a distinct cuticular lining, which can be recognized in a transparent exuvia as long tubes (1 mm) extending from the distal pores back to the venom glands. Whereas the proximal bulb has many long sensory hairs on its surface, the distal aculeus is very smooth but contains small pits with tiny club-shaped hairs. These are probably contact chemoreceptors. The advantage of such sunken sensory hairs is certainly that the stinger can penetrate into prey (or foe) but can still perceive mechanical or chemical stimuli. Additionally, the aculeus bears several slit sensilla and numerous fine pores of unknown function. The aculeus is thus not only a well-adapted injection device but also contains sensory structures, which provide information on mechanical and chemical input.

We describe for the first time the behavior “Intense Leg Tapping (ILT)” being used in a prey-predator context between the Neotropical harvestman Mischonyx cuspidatus (Roewer 1913) and the syntopic spider Ctenus ornatus (Keyserling 1877). Previously, the harvestman's repeated fast dorsoventral movements of legs II had only been described during conspecific male-male interactions. We suggest it has a defensive function.

Phrynus longipes (Pocock 1894) is a top predator among arboreal invertebrates in the Luquillo Mountains of Puerto Rico, but many aspects of its ecology remain poorly understood. We sampled four of the most abundant tree species in the Luquillo Mountains during the dry and wet seasons of 2008 to evaluate microhabitat preferences of this species. In the dry season, P. longipes occurred significantly less frequently on a palm, Prestoea acuminata var. montana (Arecaceae), than the other tree species. Carapace length and the diameter of the tree on which an individual was found were positively correlated, suggesting competition for substrates. Microhabitat selection shifted in the wet season. Individuals occurred as frequently on P. acuminata as on any other species. The seasonal shift in substrate use could result from altered distribution or abundance of prey, an ontogenetic shift in substrate preference or greater competition arising from an increased abundance of P. longipes.

The natural prey of medium-sized juvenile (ca. 3 mm) crab spiders Xysticus marmoratus Thorell 1875 inhabiting Eryngium biebersteinianum plants was studied on the Absheron Peninsula, Azerbaijan. The percentage of specimens found feeding on prey was low (3.4%). Xysticus marmoratus is a polyphagous predator with representatives of four arthropod orders found in its diet. The primary food of X. marmoratus was ants (Formicidae), which accounted for 83.3% of the total number of prey. The length of prey killed by X. marmoratus ranged between 0.87–7.50 mm (mean 2.96 mm) and constituted from 28.5–300.0% (mean 96.9%) of the length of their captors. The most frequently captured size group of prey was 50–70% the length of the spiders.