Spiders in many families are capable of locomotion on the surface of water, a capability that, at its simplest, requires only a strongly hydrophobic integument and the same postures and motions that are used on land. Specialized aquatic gaits, in contrast, are only characteristic in the Pisauridae, Trechaleidae, Ctenidae, and Tetragnathidae. They are less common features of aquatic locomotion in Lycosidae, are only occasionally encountered in Salticidae, and are rare in Araneidae. Most of what is known about the biomechanics of these specialized gaits comes from research on fishing spiders (Pisauridae) and, because the physics and hydrodynamics are similar in many respects, on water striders (Insecta: Hemiptera: Gerridae). In what follows, I have concentrated on the biomechanics of propulsion in water-walking spiders and water striders because propulsion on the air-water interface was mysterious until the 1990s when researchers began seeking answers to the central question: What provides the resistance against which a spider or water strider pushes when it sweeps its legs backward? The answers, now nearly complete, include a) dimple distortion, b) drag, c) generation of vortices, and d) nanoscale brushing of the water surface by hydrophilic hairs.

To the extent that sperm production or mating opportunities are limited, males are expected to allocate their sperm optimally, so as to increase their overall fitness. Among spiders, sperm depletion and monogyny are known to be optimal male mating decisions either under strong sperm competition or as terminal investment strategies, when future mating opportunities are limited. In a medium-sized wolf spider, Hogna radiata (Latreille 1817), we investigated sperm depletion, terminal sperm investment and the potential for sperm competition in laboratory mating trials in which we allowed males and females to pair sequentially with two mates. Males mated with as many females as they encountered. We found no evidence of sperm depletion or terminal sperm investment, as mating duration and female fitness were unaffected by male mating history or age. Polyandry was rare and did not involve any clear fitness benefit to females, whereas pre-mating sexual cannibalism was a rather common outcome of mating interactions involving inseminated females. Our results indicate that H. radiata males are not sperm limited and support the hypothesis that the potential for sperm competition shapes the evolution of sperm allocation in this species. Monandrous females do not incur any fitness cost and could potentially benefit from cannibalizing their prospective mates.

The study of courtship behavior provides a useful tool for identifying cryptic species due to the qualitative differences that can be observed in closely related species. Here, we present an overview of visual courtship displays of 26 European species of the genus Pardosa C.L. Koch 1847, including new quantitative and qualitative data. Thirty-five recurring courtship elements are described and illustrated by means of drawings, photos and videos (available online). In general terms, complex movements of the palps, the first pair of legs and the abdomen characterize courtship displays in the genus Pardosa. The most complex movements are performed by the palps, while legs and abdomen mainly oscillate in the air or vibrate on the substrate. We noticed a high level of complexity in almost all of the species, both in terms of sensory modes involved and number of courtship elements composing the displays. No apparent relationships emerged when considering ethological similarities among species, attesting to the relative independence between morphological and ethological characters.

We describe here the phenological patterns of the 25 most common ballooning species of spiders caught by a 12.2 m suction trap during an eleven year survey in Switzerland. We aimed at identifying and quantifying the number, position, spread, and relative weight of activity periods for the whole community. Further, we explored the possible link between phenological patterns and habitat use. For this purpose, we used bump-hunting approaches and fitted mixtures of normal distributions to the abundance data. The phenologies can be grouped in four categories, from uni- to quadrimodal. The specific peaks in the timing of ballooning were found between February and November, with most ballooning activity occurring in summer and autumn. For some taxa, it was possible to analyze the data for young instars and adults. For the majority of taxa, the adults' peak appeared between the early and late peaks of immature individuals. Species inhabiting the ground level of open areas, often disturbed by agricultural practices, were clearly dominant in the multimodal categories; spiders living in more closed and stable habitats, such as tree-shrub and herb layers, typically had a single peak of adult dispersal. This discrepancy in phenology may simply reflect different numbers of generations, but may also result from an adaptation to maximize the persistence of populations in unstable habitats.

Trapdoor spiders are challenging to sample using active searching methods because of their cryptic burrowing behavior. This poses problems for ecological studies and for gathering the data needed for conservation assessments. Pitfall trapping provides an alternative method that targets adult males as they wander from their burrows in search of females. Using pitfall trapping requires considerations of the timing of sampling within the year, the effects of environmental conditions on spider activity, and sampling effort required for a high probability of detecting species that are present at a sample site. To investigate these factors, pitfall-trapping surveys were conducted at several localities in Gauteng Province, South Africa. The results showed that trapdoor spider activity occurs in all seasons. Each species has a discrete period of activity ranging from a few weeks to several months in duration. Some species are active at different times of the year at different localities. Statistical analysis showed soil moisture as the only significant predictor of activity from amongst seven environmental variables, and the survey results indicate that trapdoor spiders are active under wet conditions following rainfall. Between two and seven nights of trapping are required for a high probability of detecting all species present and active at a site, using the trap design employed for this study with ten trap arrays per site. Trapping must be repeated at regular intervals throughout the year in order to obtain a near complete inventory of the species assemblage. The number of species collected ranged from two to eight per site, with most sites having six or eight species. Pitfall trapping yielded 1.2–3.0 times the number of species obtained by active searching at sites where both methods were employed. Guidelines for planning pitfall-trapping surveys of trapdoor spiders are presented and future research directions are discussed.

We investigated the effects of area, age, vegetation structure and landscape features of set-asides on the spiders of the herb layer. We caught the spiders using a semi-quantitative sweep netting of the herb stratum in 160 sampling plots at 32 set-asides in the northeastern lowland of Brandenburg, Germany, from May through August 2001. We analyzed the data using multiple linear regression. The results revealed the following. 1) Vegetation height was the most influential factor increasing the number of species and individuals of particular araneid species at the set-asides. 2) Vegetation cover had no significant effect on the total number of species, but did affect the abundance of particular araneid and linyphiid species. 3) Time since the set-aside establishment and time since last management had no significant influence on the number of species, the number of individuals of particular species, the number of individuals of the ecological group “preferred habitat type.” 4) Different types of vegetation structures were used by spider families and araneid species in different ways; the abundance of some araneids benefited from high (dense or sparse) vegetation, whereas linyphiids only benefited from dense vegetation cover.

The sympatric occurrence of species is thought to be based mainly on the differences in their use of habitat and of limiting resources. Segregating parameters may be of spatial or temporal character and may include behavioral differences. We hypothesized that species of large hunting spider living sympatrically in a Costa Rican lowland rain forest should differ in their habitat and/or hunting microhabitat preferences, in daily activity pattern, and, as an adaptation to the preferred hunting microhabitat, in their specific ability to adhere to smooth surfaces. We found an assemblage of eight large species of the families Ctenidae and Trechaleidae, consisting of three subguilds: 1) two semi-aquatic species with low adhesion ability, 2) three forest-floor dwelling species with good adhesion ability, and 3) three vegetation dwelling species showing very good adhesion ability. The species were partially segregated by habitat type, with two of the vegetation dwelling species preferring the treeless area of a temporary swamp. We found no species-specific differences in daily activity patterns. The similarity in community structure between this Costa Rican and a central Amazonian assemblage suggests the existence of similar structuring mechanisms in wandering spider assemblages in climatically similar biomes.

Establishment of communities is a dynamic process initiated by immigration. Therefore, movements of individuals within a metacommunity are important for maintaining and increasing species distribution. We present results of a small landscape-level experiment that manipulated habitat size and diversity. We examined the rates of colonization of spider species, and the richness, abundance and composition of foliage-dwelling spiders. Estimation of colonization rates was based on maximum likelihood. The experimental landscape was composed of five blocks with four patches (two large, 1 m²; two small, 0.25 m²). Less diverse patches had seedlings of one plant species, whereas more diverse patches had four species with diverse structures. Eight periodic censuses of spiders arriving in the patches were performed (average interval between censuses, 28 days). The initial composition of colonizers was significantly different from the final composition, but rates of colonization did not differ between sizes and diversities, or their interaction. Abundances of spiders were positively influenced by patch size. Compositions in each temporal sample were determined by differences in the species pool migrating and arriving at an experimental landscape irrespective of habitat size or diversity. Larger patches were more likely to receive more colonists representing a wider array of species than small patches. The probability of colonization was independent of patch size and diversity, which contradicts theoretical predictions. The results highlight the high colonization capacity of spiders on spatial and temporal scales.

The fauna of surface-active spiders was studied in 12 cereal fields, with two types of subcrop, and in four young (17 months old) perennial leys (grass/clover). The fields were located in the southeastern (A), central (B) and western (C) parts of Norway. In total, 3945 spiders were caught from May to September 2004, using pitfall traps. Linyphidae was the most numerous family, with Erigone atra Blackwall 1833 representing 56% of all trapped individuals. The total numbers of spider species and individuals were significantly higher in leys than in barley at sites where both crops were present (sites A and B), with on average 11 species and 93 specimens in barley, and 20 species and 393 specimens in leys. Thus, young perennial leys appeared to provide a better habitat for spiders than did cereal fields, as has previously been documented for older perennial leys. The use of multi-species crops instead of a single crop species undersown in cereals, tended to result in higher spider species diversity, but it did not influence the total number of specimens. An ordination (DCA) showed a clustering of the spider fauna from the same site, but no clear separation between main crop types (ley vs. barley) was apparent. The main crops, subcrops, and the surrounding environs of the cropped field seem to affect the diversity and abundance of spiders.

Information regarding the eggs and egg sacs of spiders found in agricultural crops in the San Joaquin Valley of California's Central Valley is presented as a feasibility study to aid inspection of international commerce. Egg diameter showed little variation within a species and strong variation among species; hence, it is a valuable diagnostic feature. Egg quantity per sac and sac dimensions showed greater and overlapping variation, yet are still somewhat diagnostic depending on the species. Least diagnostic was the phenology of egg sac production, but this characteristic was still useful in determining that some species finish producing egg sacs prior to crop harvest, indicating that they would not be found in transported produce. A diagnostic key utilizing the most useful of these features is provided. Overall, it appears likely that if keys regarding spider eggs and egg sacs could be developed, they could provide useful information in a real world economic situation.

With 30 species and a natural distribution in North America, 28 confined to Mexico, Physocyclus Simon 1893 is the most diverse genus within the pholcid spider subfamily Arteminae. This paper provides the first phylogenetic test of the genus's monophyly through a cladistic analysis of 54 morphological characters using equal and implied weighting. The equally weighted analysis found 12 most parsimonious trees, whereas the analysis with implied weights varying the concavity values (K  =  6–10) found five or six most parsimonious trees. The monophyly of the genus Physocyclus is supported by three synaphomorphies: 1) the paired ventral apophysis on the anterior part of the epigynum; 2) the lateral constraints in the middle part of the epigynum; and 3) the arc of the uterus, with a single sclerotized projection on the anterior part. The genus Physocyclus contains two clades treated as species groups: the globosus group, with 11 species, and the dugesi group with 19 species. The species relationships within the globosus group were better resolved than those in the dugesi group. The globosus group has a biogeographical distribution pattern in the Mesoamerican and Mexican Mountain biotic components, whereas the dugesi group has a distribution pattern in the Mesoamerican and Continental Nearctic biotic components. Given the complex biogeography in Mexico, apparently a large-scale vicariant event separated the two major clades within the genus Physocyclus.

Three new species of the harvestmen genus Protimesius Roewer 1913 are described from the Amazonian region of Peru. Protimesius amigos n. sp. from Madre de Dios Department may be distinguished by the absence of an anterior prominence on the prosoma and the presence of five pairs of basal large setae on the penis. Protimesius machiguenga n. sp. and P. kakinte n. sp. are described from the Lower Urubamba region of Cusco Department; P. machiguenga n. sp. is similar to P. cirio Villarreal-Manzanilla & Pinto-da-Rocha 2006 and can be distinguished from it by the presence of a conspicuous dorsal prolateral row of tubercles on the male tibia IV; P. kakinte n. sp. is similar to P. amphichelis Roewer 1931 and P. boibumba Villarreal-Manzanilla & Pinto-da-Rocha 2006, but can be separated from these by the development of tubercles on the femur and tibia IV, and by the number of retrolateral tubercles on male femur IV. New records of P. albilineatus (Roewer 1957) from Loreto department in northern Peru are also reported.

The life history of a palpigrade is reconstructed through morphological and morphometric multivariate analyses applied to a series of 37 individuals collected in a single locality in Tlalnepantla, Estado de México, during different seasons. Those analyses reveal the presence of three life stages: protonymph, deutonymph and adult. Morphologically, males and females can be distinguished as deutonymphs and adults. Morphometrically the sexes can be recognized in all of the life stages, unprecedented for the family Eukoeniidae.

Using the road tarantula Eupalaestrus weijenberghi (Thorell 1894), we tested the importance of the third pair of legs in male courtship behavior. Our results showed that the third pair of legs is essential for males to elicit female sexual receptivity. Males with their second pair of legs immobilized elicited receptive responses from females, but males with the third legs immobilized did not. The potential role of the third pair of legs in the generation and/or transmission of seismic signals via the substrate is discussed.

The Ariadna spiders (Araneae: Segestriidae) inhabiting the gravel plains of the Central Namib Desert construct individual burrows with a circular entrance surrounded by a ring of small pebbles; sometimes they close their burrows by a small stone. In the lichen fields, about 20 km east of Walvis Bay (Namibia), there is a consistent population of Ariadna spiders that can also use pieces of lichen both in the ring composition and as the plug when the burrow is closed. We sampled and monitored 175 burrows repeatedly between December 1999 and August 2000. In March 2000, an exceptionally high rainfall occurred in the Namib, leading to flooding even in our fieldwork station. We tested whether and to what extent an event of this magnitude could affect burrow closing. We found the rain event increased burrow closure by large, but not small or medium-sized, Ariadna sp. We suggest that the flooding event acted as an ecological resource pulse for these spiders.

Relatively little is known about the food habits of neotropical harvestmen. We used Erginulus clavotibialis (Pickard-Cambridge 1905), a locally abundant species of cosmetid harvestman in Belize, in a food choice experiment. Individuals were presented with fresh fruit (pineapple) and live invertebrate prey (termites) in an experimental chamber. This species showed a strong preference for fruit, as 72% of individuals ate it first and 67% spent the most time in the fruit-containing portion of the experimental chamber. Five E. clavotibialis (13%) consumed termites, confirming this species' ability to capture and consume live invertebrate prey. Adult males located food more quickly than nymphs. Harvestmen feeding on fruit were also significantly more active than non-feeding individuals or those preying upon termites first. Opportunistic frugivory may be important to E. clavotibialis during times when fruit is available (e.g., wet season). We hypothesize that this species exhibits a generalist diet in the field.

Brachistosternus Pocock 1893 is the most diverse genus of the scorpion family Bothriuridae. Only four species of the genus have been cytogenetically analyzed so far. We report herein the cytogenetic analysis of Brachistosternus alienus Lönnberg 1898 from Comallo (Río Negro province, Argentina). This species is widely distributed in the Monte phytogeographic province, located in central and northern Argentine Patagonia. Meiotic cells of B. alienus from Comallo show 23 homomorphic achiasmatic bivalents. The karyotype of this species contains scarce AT-rich regions that may be associated with the heterochromatin of centromeric regions. Giacomozzi (1977) reports n  =  14 for B. alienus from Chubut province. Unfortunately, it is not presently possible to determine if those specimens correspond to B. alienus or to a sympatric species, Brachistosternus angustimanus Ojanguren-Affilastro & Roig-Alsina 2001. These different chromosome numbers of the two populations analyzed may reflect the occurrence of a chromosomal polytypism in B. alienus, or they may characterize different species.