Genetically modified crops expressing insecticidal proteins from Bacillus thuringiensis (Bt) have dramatically increased in acreage since their introduction in the mid-1990's. Although the insecticidal mechanisms of Bt target specific pests, concerns persist regarding direct and indirect effects on non-target organisms. In the field, spiders may be exposed to Bt toxins via multiple routes, including phytophagy and pollenivory, consumption of Bt-containing prey, and soil exudates in the detrital food web. Beyond direct toxicity, Bt crops may also have indirect impacts, including pleiotropic and prey-mediated effects. Here, we comprehensively review the literature and use meta-analyses to reveal that foliar spider abundance is unaffected by Bt corn and eggplant, while cotton and rice revealed minor negative effects and there were positive effects from potato. Moreover, the soil-dwelling community of spiders was unaffected by Bt corn and cotton, while positively impacted in potato. However, Bt crops had higher populations of both foliar and epigeal spiders than insecticide-treated non-Bt crops. The current risk-assessment literature has several caveats that could limit interpretations of the data, including lack of taxonomic resolution and sampling methods that bias the results in favor of certain spiders. These families responded differently to Bt crops, and spider responses to insecticides are species- and toxin-specific, thus highlighting the need for greater taxonomic resolution. Bt crops have become a prominent, and increasingly dominant, part of the agricultural landscape; understanding their interactions with spiders, a diverse and integral component of agroecosystems, is therefore essential.

We collected data on maternal mass, clutch mass (reproductive effort), number of offspring, and mean offspring mass from 28 species of Lycosidae (wolf spiders) and five species of Pisauridae (nursery-web spiders) found in Mississippi, USA. Our primary goal was to test for a trade-off between offspring number and offspring size (mass) among wolf and nursery-web spiders, which are sister families. The regression of reproductive effort on maternal mass was highly significant and explained 94% of the variation in reproductive effort among species and 96% of the variation among genera. The slope of the regression line between maternal mass and total offspring mass was not significantly different from one, suggesting that spiders used a constant proportion of their total energy budget for reproduction regardless of size. Partial correlation and principal components analyses demonstrated a clear trade-off between offspring size and number. Species with large offspring (relative to adult size) produced fewer offspring than expected. Lycosids produced small numbers of large offspring relative to pisaurids, and smaller species of both families are more constrained in the evolution of the offspring size:number continuum than larger ones.

Three Draconarius species collected from the Tiantangzhai National Forest Park, China are studied, including two new species, D. peregrinus sp. nov. and D. tiantangensis sp. nov. The male D. molluscus (Wang et al. 1990) is reported for the first time.

Temperature strongly affects spider metabolic rate. Consequently, quantifying a species' temperature-metabolism relationship is useful in evaluating consequences of choices that affect body temperature. Body size also influences metabolic rate, and body size in spiders is strongly impacted by feeding and reproductive condition. Using adult female crab spiders, Misumenoides formosipes Walckenaer 1837 and Mecaphesa asperata (Hentz 1847) (formerly Misumenops asperatus) acclimated to field ambient conditions, I measured standard metabolic rates (SMR) over an ecologically relevant temperature range (10–40° C). I controlled hunger and reproductive condition of M. formosipes using starved (25 days post-feeding) or fed (7 days post-feeding) spiders, and virgin or mated spiders; in experiments with M. asperata, I used fed spiders of unknown reproductive status. Temperature strongly affected crab spider SMR, and both species showed similar temperature-SMR relationships. Mecaphesa asperata displayed equivalent temperature coefficients (Q₁₀s – the factor by which a physiologic process changes with temperature) for SMR across the experimental temperature range, while M. formosipes had significantly higher Q₁₀ at low temperature than at mid-range or high temperature; Q₁₀s of the two species reflected previously determined impacts of temperature on hunting performance. Influence of hunger-reproductive condition on SMR of M. formosipes depended on how I accounted for body size; regardless of method, gravid spiders did not show elevated metabolic rate. Lastly, I combined crab spider SMR data with published SMR data to generate mass-metabolism equations for spiders; mass-scaling exponents approximated 0.67.

Most spiders are aggressive, socially intolerant predators; however, broods develop inside a common site and thus should benefit from restraining aggression at this time and until they disperse. I tested single and mixed-brood groups of Misumena vatia (Clerck 1757) (Thomisidae) spiderlings that had just emerged from their nests to determine whether they cannibalized other young under crowded conditions comparable to the immediate area of their nests, and if so, whether they distinguished between sibs and non-sibs. Young M. vatia provide an interesting test case, since some broods remain in close contact for a short period of time after emerging from their nests. Mortality remained low over one month in provisioned young under crowded conditions, and no cannibalism occurred in these individuals. Cannibalism remained low in most broods of unprovisioned young, even though most of them eventually starved over this time. Just-emerged spiderlings placed in the field for three days and then run similarly also showed initially low tendencies toward cannibalism. However, larger free-ranging spiderlings that overlapped in size with provisioned spiderlings in the study cannibalized freely when confined similarly to the other spiderlings in this study. During this period the spiderlings showed no clear evidence of distinguishing between sibs and non-sibs.

Mesobuthus karshius new species from the southern region of Xinjiang, China, is described. Nine species and subspecies of the genus Mesobuthus Vachon 1950 from China are recorded, and diagnoses of M. eupeus mongolicus (Birula 1911), M. eupeus thersites (C.L. Koch 1839) and M. martensii martensii (Karsch 1879) are provided. In addition, M. caucasicus przewalskii (Birula 1897), M. caucasicus intermedius (Birula 1897), M. eupeus mongolicus (Birula 1911), M. karshius sp. nov. and M. martensii martensii (Karsch 1879) are illustrated, and a key to the Chinese Mesobuthus is also provided.

Females of the leaf-curling sac spider Clubiona riparia build three-sided capsules, in which they enclose both themselves and their eggs. A capsule is usually constructed by bending a single blade of grass or other leaf twice, each time causing a fold that is perpendicular to the long axis of the blade, and joining the edges with silk. When constructed with monocot leaf blades, the resulting capsule is roughly triangular in cross section and 2–4 times as long as it is wide. We sampled occupied capsules from a 0.16–hectare marsh in central Ontario, Canada. Although we found capsules built with the leaves of cattails (Typha latifolia), iris (Iris versicolor), a grass (Calamagrostis sp.), and an unidentified willow shrub (Salix sp.), for the current analysis we concentrated on the monocots because of their structural similarity. Capsules built on cattails (2.13 ± 0.14 ml) were more voluminous than those on iris (1.63 ± 0.14 ml), and capsules made of grass blades (0.67 ± 0.08 ml) were the smallest. Nearly 70% of the total variation in capsule volume was associated with differences between the plant species. Only among capsules built on cattails was there a significant positive relationship between pre-oviposition spider mass and capsule volume; it accounted for about 37% of the variability in capsule volume. On willow leaves, spiders always constructed capsules with the lower surface of the leaf to the inside of the capsule; and on cattail blades, spiders always made their bends in a clockwise direction. We discuss the implications of our findings for an understanding of the choices these spiders make just prior to oviposition.

Funnel-web spinning spiders of the genus Hololena are capable of fast movements in a horizontal plane across a variety of challenging surfaces. We used two species, H. curta (McCook 1894) and H. adnexa (Chamberlin & Gertsch 1929), in experiments designed to reveal how they achieve remarkable speeds, occasionally exceeding 70 body lengths (∼50 cm) per second. In high-speed recordings we found that spiders used their legs in alternating sets of four, distributed in staggered pairs along the body axis, resulting in an alternating-tetrapod gait. Increases in speed showed positive linear relationships with both frequency and stride length. There were also inverse, linear relationships in both species between speed and duty factor, meaning that increases in speed are associated with a decrease in the relative amount of time spent by the legs on the ground during each full leg cycle. By examining their duty factor vs. speed regressions, we found that spiders of both species were capable of aerial phases during high-speed running, with the transitional speed occurring at an average of 54 body lengths per second. We conclude that further experimentation with high-speed spiders and insects will likely show that a variety of species exhibits dynamically stable locomotion, including aerial phases.

In Central America, the family Manaosbiidae is recorded only from Panama and Costa Rica. Four species occur in this region: Barrona williamsi Goodnight & Goodnight 1942, Bugabitia triacantha Roewer 1915, Poassa limbata Roewer 1943, and Zygopachylus albomarginis Chamberlin 1925. In this paper, we describe Barrona felgenhaueri new species (Coclé Province, Panama) and Bugabitia akini new species (Coclé Province, Panama) and report a new record for B. williamsi (Coclé Province, Panama). We used SEM to examine the penis morphology of Barrona Goodnight & Goodnight 1942 and the Caribbean species Cranellus montgomeryi Goodnight & Goodnight 1947 and Rhopalocranaus albilineatus Roewer 1932. We compared genital morphology of these species with published descriptions for Manaosbiidae from South America. With respect to genital morphology, we found that the most variable characters were the number and relative sizes of the setae that occur on the lateral margins of the ventral plate. Other features that exhibited interspecific variation included the shape of the ventral plate, the shape of the distal border of the ventral plate, and the shape and armature of the apex of the stylus.

Spiders are effectively blind with respect to the lines in their webs, and they commonly use exploratory leg movements to find lines, just as a blind man finds objects using a cane. Nevertheless, a mature female Leucauge mariana (Keyserling 1881), which spins a relatively open, sparsely-meshed hub and whose legs I and II hold widely-spaced radii rather than dense hub lines, turns precisely and rapidly when prey strike her orb. She can turn > 90°, finding and grasping new lines with all her legs, in as little as 0.1 s and can reach a prey several body lengths away in as little as 0.23 s after impact. The hub design and resting postures of the spider's legs allow her to sense where the prey strikes the web, generate the force necessary to turn her body rapidly, and find lines to grasp. The spider may move most (if not all) of her legs, without obtaining further guidance information once the leg has begun to move until it nears the site where it will grasp a line. The order in which legs are moved is relatively consistent, and each tarsus moves to a site where lines are relatively abundant; some then make small, quick searching movements to find and grasp lines there. When radial lines were experimentally cut near the hub in a sector in which a prey was subsequently introduced, legs I and II first made small searching movements, and then executed much larger searching movements. The rapid leg movements directed toward specific areas where lines are abundant, and the small searching movements employed at these sites suggest that the spider modifies her behavior when she is at the hub of an orb.

Predaceous arthropods such as spiders are often adapted to hunting sites where their hunting success is greatest. We investigated the responses of two spiders to phytochemical cues that they potentially experience while hunting on leaves or flowers, and how these cues could influence their decisions where to forage. We compared the behavior of two sit-and-wait predators, Pisaura mirabilis and Misumena vatia, which hunt predominantly in the vegetation or on flowers, respectively. In choice tests, P. mirabilis frequently preferred leaves and leaf extracts to flowers and floral extracts and avoided substrates treated with the common floral scents β-caryophyllene and nerolidol (sesquiterpenes) in natural concentrations. In contrast, M. vatia did not show any preferences for any of the substrates and treatments offered. The lack of responses by M. vatia contrasts with earlier studies on another crab spider species (Thomisus spectabilis) that used phytochemical cues as a guide to rewarding flowers. The avoidance of many flowers, their extracts, and the floral scent compounds by P. mirabilis suggests that these cues may prevent the visitation by this and other generalised predators that potentially decrease the pollination success of a plant.

Homalonychus selenopoides Marx 1891 is endemic to the coastal plains of the Sonoran Desert in the state of Sonora, Mexico and the southwestern United States. Although the species was described more than a century ago, nothing is known about its behavior. We collected spiders in the southern Sonoran Desert to study their reproductive behavior, which we recorded with an infrared camera, mainly at night. Sperm induction was of an indirect type; males wove a triangular sperm web about 2 cm² near the ground. Females and males prepared threads of silk and sand. Courtship behavior was intermediate between levels I and II, and the copulation position was a modification of type III, where the male tied the female's legs with silk before mating. Sexual cannibalism may occur during mating. Females began to spin their egg sac at ∼11 days after mating and completed it in ∼15 h, including ovipositioning. The outer layer of the egg sac contained sand, and the sac was surrounded by a garniture of cords of silk and sand, possibly to protect the eggs from desiccation and as a barrier to parasites and predators.

The function of silk web decorations in orb weaving spiders has been debated for decades. The most accepted hypothesized functions are that web decorations 1) provide camouflage against predators, 2) are an advertisement for vertebrates to avoid web damage, or 3) increase the attraction of prey to the web. Most studies have focused on only a few genera, Argiope being the most common. In this study, I evaluated the prey attraction hypothesis of silk decorations for a species of a poorly studied genus in this topic, Micrathena sexpinosa Hahn 1822. I used a web-choice experiment in which I presented empty or web-bearing frames at the end of a tunnel to stingless bees (Tetragonisca angustula). This frame-choice experiment consisted of the following comparisons: decorated web vs. empty frame, decorated web vs. undecorated web, and undecorated web vs. empty frame. Webs with decoration intercepted significantly more bees than empty frames and undecorated webs. Therefore, the decorations of Micrathena sexpinosa might play a role in increasing foraging success.

We investigated the trophic strategy of Mexcala elegans Peckham & Peckham 1903, an ant-eating salticid spider from South Africa, in order to gain baseline information concerning the evolution of prey specialization. We studied its natural prey, prey acceptance, and choice using a variety of prey species. In its natural habitat, the spider captured only ants, mainly its mimetic model Camponotus cinctellus, indicating that the species is a stenophagous ant-eater. However, in the laboratory, M. elegans captured 12 different invertebrate taxa with efficiency similar to the capture of ants, suggesting that it is euryphagous. For the capture of ants but not for other prey, it used a specialized prey-capture behavior. In prey-choice experiments, the spiders did not prefer ants to flies. We found no evidence for neural and behavioral constraints related to identification and handling of prey. Our results suggest that M. elegans is a euryphagous specialist using a specialized ant-eating capture strategy in which prey specialization has evolved as a byproduct of risk aversion (“enemy-free space” hypothesis).

We used data from 33 species of cursorial spiders in northern Mississippi (USA) to investigate the relative contributions of ecology and phylogeny to the reproductive trade-off between number and size of offspring. Sixty percent of the variation among genera for female reproductive allocation was due to differences between the family Pisauridae and the family Lycosidae. Temporal variation in reproductive allocation during the reproductive season was not observed for the majority of species examined. We found significantly different patterns of reproductive allocation among species within genera, suggesting that each species has responded to distinct selection pressures. Preliminarily, this extensive variation appears to be due mostly to interspecific competition and predation risk from other spiders. However, the patterns of reproductive allocation of species within a single guild (i.e., a group of species potentially competing for the same resources) for the two families are very different. Larger species of wolf spiders (family Lycosidae) within a given guild produce smaller numbers of larger offspring relative to the size of the mother, and smaller species produce the reverse. However, in nursery-web spiders (family Pisauridae) the larger species within a guild produce larger numbers of smaller offspring than expected. The current study provides an example of the flexibility of life history evolution despite phylogenetic constraints. It also demonstrates the potential for varying life history strategies to mediate competition, allowing similar species to coexist.

The arachnid order Opiliones, and the suborder Cyphophthalmi in particular, have recently been used to test biogeographical patterns in Southeast Asia due to their ancient age and extremely low vagility. Here we report the first Cyphophthalmi—two juveniles—known from Mindanao in the southern Philippine Archipelago, and we place them in a molecular phylogeny to test biogeographical hypotheses for their colonization of that island. Five molecular markers were sequenced from one specimen, three from the other, and these sequences were added to a previously completed phylogenetic analysis. The specimens were recovered as members of a clade found almost exclusively on Borneo. Their deep placement within this clade suggests a very old origin and colonization that perhaps involved the mysterious landmass now underlying Mindanao's Zamboanga Peninsula. This species prompts new questions about the abilities of Southeast Asian Cyphophthalmi (Stylocellidae) to disperse and colonize, and it emphasizes how much remains to be understood about the geological history of the Philippines.

The natural diets of many terrestrial predators such as spiders have yet to be investigated. In this study, I analyzed the diet of a web-building spider, Latrodectus hesperus Chamberlin & Ivie (1935), over one year in a natural habitat of coastal British Columbia, Canada. This is the first study to document the natural diet of L. hesperus over several months. I identified and measured 1599 prey items collected from L. hesperus webs and web sites between January and December. Spiders fed on ground-active prey from eight different orders of arthropods. Coleoptera and Hymenoptera were the predominant prey of L. hesperus in this habitat, combinely accounting for > 85% of the total prey catches and biomass. The other prey orders included, in order of abundance, Isopoda, Araneae, Dermaptera, Orthoptera, Lepidoptera and Diptera. Spiders captured prey mostly between May and October, when females oviposit, juveniles grow, and prey are most active. These results show that L. hesperus is a polyphagous predator that feeds primarily on prey from two orders of insects.

Energetic costs of courtship behavior were measured for two sympatric wolf spiders that are reproductively isolated based on distinct male courtship behaviors with different signaling modes and activity levels: Schizocosa ocreata (Hentz 1844) uses multi-modal communication (visual and seismic signals) and an actively-moving courtship display, whereas S. rovneri (Uetz & Dondale 1979) uses only seismic signals produced while stationary. To test for increased energetic expense of more complex multimodal courtship in S. ocreata, we recorded peak CO₂ output for male spiders standing, walking, or courting. We found that peak CO₂ output while standing or walking was similar between species. Courtship behavior of S. ocreata produced greater peak CO₂ output than these other behaviors, and was significantly greater than peak CO₂ output of S. rovneri courtship, which was not different from that of locomotion. Hence, unequal energy expenditure related to the modality of the males' courtship displays resulted in different energetic costs for courting male spiders. Male courtship vigor may serve as a criterion for female mate choice in Schizocosa.

About 1% of the nests of a crab spider (Misumena vatia [Clerck 1757]) population in coastal Maine, USA, contained apparently cannibalistic individuals. These spiderlings remained in their nests over three times longer than average and attained average masses twice that of non-cannibalistic spiderlings (maximum  =  four-fold) before dispersing. Parents of the 14 cannibalistic broods came from 10 sites separated from each other by 0.5–10 km and over 23 years; thus, this behavior appears to be widespread and relatively stable, though uncommon.

We counted and measured Sphodros rufipes (Latreille 1829) pursewebs in two survey plots on Tuckernuck Island, Massachusetts. Our objectives were to quantify web density, record physical web characteristics and determine the main components of S. rufipes' diet. We counted 479 webs in the two plots and report web densities between 0.058 and 0.18 webs/m², denser than previously reported populations. Webs were not distributed evenly, and densities ranged from 0 to 0.38 webs/m². Aggregation indices suggest that webs are aggregated on a landscape level, but are more evenly distributed at a local level. Contrary to most previously published literature on S. rufipes, we noted the predominance of the grass-like sedge, Carex pensylvanica, rather than trees, as a web support. Coleopterans and isopods made up 79 percent of the prey parts collected from 56 pursewebs.

Spitting spiders eject silk and glue from their fangs when attacking prey. The ejection is complete in less than 35 ms and involves high-frequency fang oscillations that can approach 1700 Hz. Because of Newtonian physical constraints, these oscillations, which cause the spit to be dispersed in a zigzag pattern, could not occur at such high frequencies if the fangs themselves were not very small. We hypothesized that allometric neoteny, in which the developmental rate of a structure is retarded relative to the changing overall size of the growing individual, could explain (in an ontological sense) the small fangs of adult spitting spiders. We measured the fangs, chelicerae, carapaces, and sterna of many sizes of spitting spiders, Scytodes thoracica (Latreille 1802a), brown recluse spiders, Loxosceles reclusa Fertsch & Mulaik 1940, and wolf spiders, Varacosa avara (Keyserling 1877), to discover whether the fangs of spitting spiders grow unusually slowly. Using sternum width as our proxy for spider size, we found that the carapaces of spitting spiders grow disproportionately fast but that the spiders' chelicerae and fangs grow at the same rate as their sterna. The growth patterns in L. reclusa and in V. avara differed both from each other and from S. thoracica. We evaluate these patterns and conclude that the diminutive fangs of adult spitting spiders do not constitute an instance of allometric neoteny.

We examine the social characteristics and sex ratio of the recently described Anelosimus oritoyacu Agnarsson 2006. We find that this spider, whose nests occur on tree crowns and bushes in open fields near Baeza, Ecuador, lives in colonies that may contain from one to several thousand adult females and their progeny. It differs from most other social congeners in that it occurs at relatively high elevations (1800–1900 m) and its primary sex ratio, 2.5 females per male, is the least biased of any known social species in the genus. The low sex ratio bias may reflect a low colony turnover rather than high gene flow among colonies, as the colonies occurred in complexes that were few and far between, but appeared to be long-lived. The relatively small body size of adult females and a web that appears to allow the capture of insects from all directions, combined with individual and group foraging, may allow the formation of large colonies at an elevation where insects, albeit abundant, are for the most part small.

Juvenile solifuges have rarely been observed hunting in natural conditions. We recorded the hunting behavior of juvenile third or fourth instar solifuges of the genus Chanbria (Eremobatidae) near lanterns set up in the Imperial Sand Dunes, Imperial County, California. At least 10 juveniles were observed between 22:50 and 01:40 h on 18–19 June 2010. The behavior consisted of nearly constant movement, abrupt stops or retreats, and quick excavation of the sand. The juveniles probed the sand using their pedipalps. One juvenile was observed to dig up an immature Hemiptera from just beneath the surface amidst the sand grains. Direct contact with other solifuges or arthropods occasionally triggered an immediate flight response.

A new Brazilian species of the genus Eukoenenia is described from a single male specimen collected within the Archimedes Passini cave, a marble cave located in the municipal district of Vargem Alta, Espírito Santo. Eukoenenia spelunca, sp. nov., has six blades on the prosomal lateral organs and a unique shape of the genital lobes. Some morphometric parameters demonstrate the specialization of this new species to the cave environment.

Sheet-webs are built by a variety of unrelated spiders. Some of these spiders are common, but information on their web construction behavior is scarce. This study describes the sheet-web construction behavior of Melpomene sp. (Agelenidae) and the sites where webs are built. I recorded the beginning of sheet-web construction by several spiders and analyzed photographs of webs in the field and the laboratory. Web construction consisted basically of two alternating behaviors: laying support threads and the filling in the sheet. These behaviors were repeated during several construction sessions until the available area was filled, or until the web reached approximately 80 cm². Apparently the spider uses both ampullate and aciniform lines for web construction, contrary to a recent description.

The primary impediment of long term, high-resolution, ecological studies of scorpions is the difficulty of marking individuals for monitoring and recapture. I tested the use of Visible Implant Elastomer (VIE) as a permanent subcuticular tagging technique in the striped bark scorpion Centruroides vittatus (Say 1821). Mortality and prey capture rates of tagged scorpions did not significantly differ from untagged controls. Tag readability was high and comparable to published studies on other arthropod groups. Animals molted (3 treated, 7 control) and gave birth (1 treated, 2 control) successfully. I recommend VIE tagging as a viable solution to what was a major impediment to the proliferation of fine-scale ecological and population-level field research in C. vittatus and similar arthropods.

In sexually cannibalistic spiders, males usually only copulate with one female. This selects for male strategies to improve paternity success in their single mate. Male mating strategies can include genital damage during female attack in some cannibalistic orb-weaving spiders, where males are dwarf and females polyandrous. We explored whether sexual cannibalism is necessary for male genital damage in the silver spider Argiope argentata (Fabricius 1775) by performing mating trials with recently killed virgin females. We found that males can break off their copulatory organs without female intervention and spontaneously die during copulation. Results suggest that genital damage evolved in response to sperm competition in this species.

In the Yucatan Peninsula, the tarantula Brachypelma vagans Ausserer 1875 is commonly associated with human settlements, as are the scorpions Centruroides gracilis Latreille 1804 and C. ochraceus Pocock 1898. Nonetheless, scorpions are virtually absent from villages showing a high density of tarantulas. Predatory interactions between these predators could explain the lack of local overlap. To test this hypothesis, we observed the behavioral interactions between B. vagans and C. gracilis or C. ochraceus in experimentally controlled conditions, and we compared these interactions to interactions between the tarantula and two prey species: cricket and cockroach. For observations, a pre-adult tarantula was placed in an experimental arena in which we introduced either a scorpion or an insect. In all, 115 trials were performed. We recorded time elapsed and behavioral responses: avoidance, attack, escape, capture, and attack success. Tarantulas preyed on all prey with the same attack success (63.8% ± 0.8%), but they attacked and captured cockroaches quicker and more often than the other prey (87% vs. 50%, and 57% vs. 30%, respectively). Scorpions attacked tarantulas in 25.5% of occasions, but they were never successful, and were killed in 9% of occasions. We conclude that tarantulas are potential predators of scorpions. Moreover, in villages where tarantulas are abundant they might prevent the presence of scorpions. Thus the presence of this non-aggressive tarantula may be beneficial from the human perspective.