Spiders construct a wide variety of silk structures, ranging from draglines to prey capture webs. Spider silks rank among the toughest materials known to science, and these material properties are critical for understanding how silk structures, such as webs, function. However, the mechanics of spider silk are often ignored in the study of webs. This review aims to show how the material properties of silk proteins, the structural properties of silk threads, and the architectures of webs ultimately interact to determine the function of orb webs during prey capture. I first provide a brief introduction into spider silk and how to characterize its material and structural properties. I then examine the function of draglines as “lifelines” to provide a well-understood example of the interaction of material and structural properties in silk function. Next, I examine how orb webs function in prey capture by first intercepting insects, then stopping their kinetic energy of flight, and finally retaining the insects long enough to be subdued by spiders. I show how variation in the material and structural properties of silk acts synergistically to facilitate the stopping and retention potentials of orb webs, and why this can occur in opposition to how orb webs intercept prey. Finally, I summarize why information on the material properties and structures of silk threads needs to be better incorporated into future investigations of spider webs in general.

Flies of the family Acroceridae are specialized internal parasitoids of spiders. We infected hatchlings of wolf spiders Pardosa prativaga (L. Koch 1870) (Araneae: Lycosidae) with larvae of Acrocera orbiculus (Fabricius 1787); most hosts were infected by a single larva, but others endured multiple infections of up to eight larvae. The infected spiders and a group of uninfected control spiders were raised in the laboratory for up to 23 weeks. We found that most (81%) spiders infected by only one larva were able to suppress the infection, whereas most multiple infections (73%) were “successful” (i.e., a larva emerged or was recovered by dissection, perhaps from a prematurely dead spider). Infected spiders had their survival reduced in proportion to the infection load, but the reduction was not significant if the infection was suppressed. Infected spiders had higher growth rates than uninfected, and growth stimulation was proportional to the number of initially infecting larvae and independent of whether the larva was suppressed or not. Due to these patterns, we suggest that growth enhancement results from the spider's mobilization of extra resources for combating the infection rather than parasitoid manipulation of spider growth. Spiders with multiple infections took longer to mature than uninfected spiders, and the pattern of instar durations was changed compared with that of control and singly infected spiders. As multiple infections were important for the parasitoid's success, we suggest that the parasitoid fly's habit of laying eggs in large clumps may be an adaptation to increase the chance of success via multiple infections.

When host organisms mount an immune response, they incur energetic costs. Theory predicts that these costs result in trade-offs between investment in life history traits (such as growth and reproduction) and investment in immune response. Recent empirical work investigating whether immune ability is impaired during sexual activity in invertebrates does not uniformly support this prediction. Here, we use lytic activity to test for trade-offs between immune ability and reproductive events in three experiments with the pholcid spider Physocyclus dugesi (Simon 1893). First, we test whether males or females have their immune response negatively affected after mating; second, we assess whether oviposition behavior affects immune response; and third, we investigate whether sexual aggression by females affects immune response. We compare reproductive and non-reproductive spiders' immune response. Our results suggest a down-regulation of immune response following mating, oviposition, and aggression. This supports the notion that immunocompetence is competing for a resource with sexual activities. We discuss reasons why such costs arise in P. dugesi.

Evarcha culicivora Wesolowska & Jackson 2003 is a jumping spider (Aranea: Salticidae) that has the distinction of being the only predator known to express an active preference for the vectors of human malaria (i.e., the mosquito genus Anopheles) and to feed indirectly on blood by choosing blood-carrying female mosquitoes as prey. Here we examine this predator's preference profile in greater detail than has been achieved before. Lures (dead prey mounted in life-like posture) were made from two mosquitoes (Anopheles gambiae and Culex quinquefasciatus) and a non-biting midge (Clinotanypus claripennis). Testing protocols were simultaneous presentation (two prey presented simultaneously), alternate day (two prey, each presented singly but on alternate days) and alternative prey (second prey presented while test spider feeding on first prey). Pre-trial fasts were 1, 7, 15 and 21 days. Findings from this combination of variables were used to estimate strengths of preferences. Besides confirming the preference of E. culicivora for blood meals and for Anopheles in particular, we provide the first evidence of a preference, independent of blood meals, for female instead of male mosquitoes. The strength of preference, measured by its persistence despite increasingly long pre-trial fasts, shows that preference for Anopheles is expressed by juveniles more strongly than by adults, but preference for blood meals is expressed by adults more strongly than by juveniles.

We characterize, in both the laboratory and the field, the preferential thermal microenvironments of Paraphysa parvula (Pocock 1903) (Araneae: Theraphosidae), a mygalomorph spider that successfully inhabits the high elevation environments of the Chilean Andes. We studied 116 spiders. Their average body temperature in the field was 31.02 ± 2.74° C, similar to the laboratory preferred temperature of 31.7 ± 2.31° C, and higher than the ideal temperature of reproductive females, 29.34 ± 2.81° C. In non-reproductive spiders, we found significant associations between body temperature and the temperatures of the air, substrate and rocks; however, the strongest association was between body and rock temperatures. Similar results were obtained in reproductive females, but there the best predictor of the body temperature was air temperature in the shelter. In both cases, the air temperature remained below body temperature and well below the temperature of the rocks and stones. Both situations show the importance of behavioral thermoregulation and the mechanisms of heat transfer into the microenvironment in the body temperature regulation of spiders. Conduction from the environment, heat transfer by small convection currents, and radiation from the hot stones constitute small environmental cues that allow these spiders to maintain an optimal temperature. The selection of shelters meeting specific temperature regimes appears to be a key condition for the optimization of female reproductive success and survival of females and juveniles in a high elevation environment.

We evaluated spider guild abundance and vegetation complexity in riparian forests in southern Brazil in four distinct river basins over 2 yr. We compared spider guild abundance among rivers, habitats (edges vs. forest interior), and against vegetation complexity. We also compared spider assemblages between juvenile and adults in terms of guilds. Of 42,057 spiders sampled, 79% were juveniles and 21% were adults. Space-web weaving was the most abundant guild whereas cursorial hunters was the least abundant one. Weaving spiders dominated over hunters (59% vs 40.58%, respectively). Thirty-four families were recorded; ambush hunters totaled 11 families; space web sheet builders and hunting runners had eight families each and there were seven families for orbicular web builders. Space web sheet builders dominated on all levels: among rivers and habitats (edges and forest interior). Unexpectedly, spider guilds did not seem to be influenced by environmental complexity, given the variables measured, under a Canonical Correspondence Analysis. There was an interaction between guild relative abundance and ontogeny, since the proportion of the space web sheet builders guild among adult spiders was larger than the proportion among juveniles, with a decrease in proportion of adults especially for hunting runners.

Spiders are important generalist predators in agroecosystems, yet early season colonization is poorly understood, especially in northern regions. We investigated colonization patterns of spiders in agricultural fields after snow-melt in four cornfields in southwestern Quebec (Canada). Paired pitfall traps were associated with two drift fences to obtain data about immigration to and emigration from the fields and were placed at increasing distances from a deciduous forest border. Control traps were placed four meters inside the forest. Seventy-four species were collected, dominated by Linyphiidae and Lycosidae. Most of the fauna was already active during the first weeks of collection, and early season assemblages differed from late season assemblages. A significant ecotone effect was found for spider abundance, species richness and species composition. This study stresses the importance of early season spider activity in agroecosystems, and this context is relevant to a period of colonization by the dominant, active spider species.

Grazing is an established conservation tool for maintaining grassland habitats and under some circumstances may enrich arthropod assemblages. However, even if enrichment occurs, it is not granted that conservation value signified by rare and specialist species will also increase. To assess how some preset levels of grazing suit conservation aims, we studied spider assemblages of ungrazed, sparsely grazed and intensively grazed areas of a pasture in Hungary for three years by pitfall trapping and suction sampling. At ground level there was no significant difference among grazing areas, while at higher strata increasing grazing intensity negatively affected number of individuals and species. C-score analysis indicated equally neutral community assembly in all three grazing areas. All statistical methods that took into account species identity indicated virtually no difference between the spider assemblages of the sparsely grazed and ungrazed areas; however, there was a marked difference between these and the intensively grazed area. Spider species in the intensive grazing area had significantly lower affinity but wider tolerance for habitat naturalness, preferred more open habitats and had a lower rarity status. In the intensive grazing area a number of disturbance-tolerant species, among them agrobionts, were present, whereas the exclusion of rare or specialist species in the intensively grazed area occurred infrequently. The primary effect seen at the intensive grazing area was the opening of the spider assemblage to disturbance-tolerant species, while species richness was likely maintained by neighboring source populations. Overall, we experienced a marked decrease in the naturalness status of the spider assemblage in the intensive grazing area.

Accurate characterization of predator-prey linkages in agroecosystems is important prior to the implementation of conservation biological programs. The Russian wheat aphid, Diuraphis noxia (Hemiptera: Aphididae), is a significant pest of wheat and barley in the United States. This research utilized molecular gut-content analysis as a minimally disruptive technique to characterize the trophic connectivity between two spider species, Tetragnatha laboriosa Hentz 1850 and Pardosa sternalis (Thorell 1877), and D. noxia. We describe the development of species-specific primers that amplify a 227 bp fragment of D. noxia COI mtDNA to identify the frequency of predation under varying aphid densities and developmental stages of winter wheat. We tested the hypotheses that predation rates on D. noxia would be highest for both spider species at the greatest aphid infestation level in the aphid-resistant wheat cultivar plots and that densities of T. laboriosa would be highest at the highest aphid infestation level in the aphid-resistant cultivars. Despite short detection periods of prey DNA in the laboratory, 32% and 48% of field-collected T. laboriosa and P. sternalis spiders screened positive for D. noxia DNA, respectively. T. laboriosa densities were highest at the highest aphid infestation level. Aphid-resistant wheat cultivars did not impact predation rates or densities. Additionally, P. sternalis predation on D. noxia increased with increasing aphid infestation levels. Given the high predation rates on D. noxia and their association with increased aphid densities, both spider species represent important natural enemies within wheat agroecosystems, and further research is required to quantify their impact on aphid populations.

Available evidence suggests that sociality in the spider genus Anelosimus Simon has evolved as a gradual transition from short-term maternal care to permanent sociality. The discovery and description of new species displaying various intermediate levels of sociality deepens our understanding of this transition. Here I use five molecular loci (28S, ITS2, COI, 16S, ND1) to phylogenetically place specimens of an intermediate-social population from Uruguay, previously and tentatively identified as the widespread and common A. studiosus (Hentz 1850). The Chinese A. chonganicus Zhu 1998 is also phylogenetically placed for the first time, and new sequences from four additional Anelosimus species and two theridiid genera (Audifia Keyserling, Tekellina Levi) are all combined with previously published data to reconstruct a novel phylogeny of Anelosimus spiders. This phylogeny recaptures previously well-established groups and reiterates well-known themes such as the multiple origin of sociality. The Uruguayan specimens nest outside of A. studiosus, and I therefore describe these as a new species, Anelosimus vierae sp. n. and summarize existing data on its behavior in the context of social evolution. I also synonymize A. tungurahua Agnarsson 2006 with A. studiosus new synonymy. Finally, I define the subfamily Anelosiminae, containing Anelosimus and Kochiura Archer; Anelosiminae is sister to the diverse Theridiinae.

A new species of trapdoor spider, Idiops rubrolimbatus sp. nov., is described from the northern part of the Western Ghats of Maharashtra. Idiops bombayensis Siliwal et al. 2005 was originally described based on only a female specimen. Here, a description of the male is provided for the first time, along with a female description based on fresh collections from Mumbai and Matheran, Maharashtra state, India. Natural history information is provided for both species.

Cyphophthalmi, commonly known as mite harvestmen, are a suborder of cryptic Opiliones with a global distribution. The genus Austropurcellia Juberthie 1988 is a lineage of mite harvestmen currently known from a small number of localities in the forests of Queensland, Australia. We describe four new species of Austropurcellia (A. alata, A. culminis, A. despectata, and A. vicina) from museum lots; each new species is known from only a single collection and few specimens. We present the first key to the species of Austropurcellia, a catalogue of known collecting localities, and a distribution map. Although our current knowledge of the diversity and distribution of this genus is certainly incomplete, it is clear that these narrow-range endemics have great potential as a system for understanding the role of historical forest fragmentation in the evolution of rainforest animals.

Diversification of morphological characteristics among geographically separated populations is particularly important in understanding evolutionary processes and is considered the early stage of allopatric speciation. In the present study, we investigated geographic variation in scorpion populations of Bothriurus bonariensis (Koch 1842). Our principal goal was to compare different populations of this species with regard to its distribution, analyzing somatic and genitalic characters. In Argentina, specimens of B. bonariensis from Entre Ríos and Corrientes Provinces are dark brown, while specimens from La Pampa have reddish coloration. Scorpions of this species from Brazil and south of Uruguay are totally black. Also, we observed variability in body size, some morphological characteristics of adult specimens (e.g., prosoma length, hand height, hand width, and telson height), and genitalic traits (e.g., hemispermatophore lamina length, basal and distal lamina width, dorsal fold length). Results indicate the presence of evident geographic variation: populations from Argentina show similar morphological patterns that differ from populations from Uruguay. We discuss these data in the context of the current phylogeographical and evolutionary knowledge of this species.

Solifuges, or camel spiders (order Solifugae), keep their pedipalps extended when moving through the environment, utilizing them much the way insects use their antennae. The male also uses his pedipalps during copulation, staying in contact with the female throughout the process. The pedipalps are covered with setae that are assumed to function as chemo-, mechano-, thermo-, hygro-, and olfactory receptors. We surveyed setal forms and other possible sensory structures on the pedipalps of solifuges to determine 1) if certain setae and structures are common to all families, 2) if some may be unique to certain families, and 3) the possible function of the various setae and other structures. We found that all families had bifurcated and tapered setae, and that all families had dorsal tarsal pores. Other setal forms were evident only in one or a few families. Three of the setal types had distal pores suggesting that they function as chemoreceptors. These data suggest that the pattern and types of setae on the pedipalps of solifuges may be phylogenetically informative and confirm that the pedipalps do function as sensory appendages.

Despite the fact that taxonomically the name Eurypelma californicum (Ausserer 1871) has been regarded as a nomen dubium and thus invalid for several decades, it is increasingly used in non-taxonomic publications and on the internet. This makes it necessary to trace back the identity of the spiders involved. The taxonomy of Eurypelma californicum and Aphonopelma hentzi (Girard 1852) was investigated, and it is concluded that the spiders referred to as Eurypelma californicum in physiological publications of the last 35 years belong to an Aphonopelma species, most likely A. hentzi.

The holotype female of Clubiona analis Thorell 1895 is examined, illustrated, and redescribed. The systematic position of the species is discussed, and a map with the type locality together with those of related species is provided.

We describe post-ovipositional maternal care in Liogonyleptoides tetracanthus Mello-Leitão 1932 (Gonyleptinae) and experimentally evaluate the protective role of this behavior against egg predation under laboratory conditions. Females laid 138.8 eggs on average and remained close to the clutch during the entire day. Eggs hatched after 11–15 days and nymphs dispersed from maternal protection after one to two days. Most of the experimental clutches left unattended were entirely consumed by conspecifics in 2–3 days. There was no reduction in egg number in the clutches protected by females. Although biological data are scarce, there are cases of egg hiding, paternal and maternal care within the subfamily Gonyleptinae. This diversity of forms of parental care is unusual when compared to other gonyleptid subfamilies, and future systematic revisions of the polyphyletic Gonyleptinae should include parental care as a potential source of phylogenetic information.

For many spiders, sex pheromones associated with female silk are important stimuli that elicit male searching and courtship behaviors. In that context, female sexual receptivity and chemical attractiveness can depend on age and reproductive status. In Paratrechalea ornata (Mello-Leitão 1943) (Araneae: Trechaleidae), males offer females a nuptial gift (a prey wrapped in silk) during courtship. Gift construction is elicited by the presence of female silk, and silk attractiveness is influenced by female age, increasing from 20 days after the female reaches adulthood. Our goal was to investigate whether female age affects female sexual receptivity and to discuss the relationship between receptivity and silk attractiveness. We exposed 26 virgin females, from 2 to 28 days after the final molt, to males offering a nuptial gift. Female sexual receptivity was age dependent and increased with adult female age. Females over 15 days from adulthood accepted more gifts than younger females, but the latency of female gift acceptance was not affected by female age. Female sexual receptivity is synchronized with chemical attractiveness, suggesting that females' pheromone release is adjusted at a particular mating age. We suggest that young virgin females may invest more in foraging and maturing gonads than in mating, accounting for the delay in receptivity and chemical attractiveness.

Temperature affects metabolic rate and egg development in mature female spiders. For temperate species, declining temperatures toward the end of the reproductive season may limit reproductive output, particularly for late-maturing females. Although spiders are known to alter their web-site preferences in response to temperature, it is unknown whether females can use web placement to overcome low temperatures that prohibit reproduction and thus extend their reproductive time frame. I surveyed web temperatures for female Nephila clavipes (Linneaus 1767) to compare female web sites and control sites at the beginning and end of the reproductive season in order to assess whether females change their web preferences in response to declining temperatures. Survey data showed that the web sites chosen by females at the end of the reproductive season have a higher minimum temperature than sites occupied during the early season. In a laboratory experiment, I addressed whether a low but biologically relevant temperature affects egg development and the female's ability to oviposit in N. clavipes. Females kept at 16° C failed to oviposit and showed signs of slowed egg development. Thus this preliminary study suggests that females may be able to protect themselves against temperatures that are prohibitively low for reproduction, but further experiments should explore the effects of temperature on egg development and web-site selection in this species.

Philoponella vicina O. Pickard-Cambridge 1899 rests on its orb web in a cryptic posture with its legs folded against its body. While feeding, the spider coats the entire prey with digestive fluid and changes its posture, spreading its anterior legs wide. We tested whether this change in leg position may function to protect against damage to its legs from its own digestive fluid. When we touched detached legs I with prey packages wetted with digestive fluid, more setae fell from the legs than when we applied tap water in a similar manner. In addition, intersegmental membranes were damaged by digestive fluid, but not by water. This and other uloborids may thus break their cryptic postures while feeding in order to avoid damage from their own digestive enzymes.