Spiders are effectively blind with respect to the lines in their own webs. Species in four orb-weaving families solved the problem of finding lines by tapping with their anterior legs, like a blind man with his cane, and then “following” these anterior legs with more posterior legs, which grasp lines that the anterior legs are already holding. Following behavior occurs during several stages of orb construction, and probably economizes on searching time and effort. The movements of following legs are finely adjusted to the morphological details of the grasping structures on their tarsi (the middle claw and its associated serrate accessory setae): the small searching movements made by following legs have consistent orientations: legs I and II move prolaterally, while legs III and IV moved retrolaterally. These orientations are appropriate to bring the asymmetrically placed middle claw and accessory setae into contact with the line. Spiders solved the additional problem of grasping lines that are more or less parallel to the long axis of the leg by using a previously unrecognized movement; they rotate the distal portion of the leg on its longitudinal axis, orienting the middle claw so that it is more or less perpendicular to the line. As an orb-weaver moves across her web, she probably constantly adjusts the rotation of each leg to align its middle claw perpendicular to the lines that it grasps.

Orb webs evolved primarily to capture prey, though they also have other functions. Recently, it has been argued that the orb web does not work as a functional unit, but instead some sections or components have presumably been shaped by selection to increase capture success of large prey (relative to the spider size). Changes in these components (e.g., an increase capture area) presumably compromise the design and function of other components (e.g., density of adhesive threads). In this study, we explore the changes in the design of orb webs throughout the ontogeny of two orb-weaving spiders of the genus Leucauge: L. mariana (Taczanowski, 1881) and L. argyra (Walckenaer, 1841). Small nymphs of both species construct webs with a relatively larger capture area and higher density of adhesive spiral loops compared to webs of larger individuals. In addition, small nymphs of L. argyra construct webs with more radii. These features probably increase the probability of capturing large prey. Some web features show different trade-offs in the two species. For instance, the number of adhesive threads increases with capture area in webs of L. mariana, but decreases in L. argyra. The density of adhesive threads in webs of both species decreases as the area of the web increases, but decreases faster in L. argyra. Thus, small nymphs are capable of optimizing different structural components of the web to increase the probability of capturing large prey, but the trade-offs between web features vary between species.

The distribution of sticky spirals and radii within orb webs is usually not uniform. Distinct patterns of silk investment in inner and outer portions of the orb may influence the web's capacity to stop and retain specific prey types. Several incidental and functional hypotheses have been proposed previously to explain the variation in web patterns. Herein, we describe the webs built by spiders of the monospecific genus Wixia O. Pickard-Cambridge, 1882 (Araneidae) and evaluate web-building hypotheses, considering the presence of a free-sector, vertical symmetry, sticky spiral distribution and radii spacing. Because all information available on the ecology of Wixia is restricted to the species that were subsequently transferred to other araneid genera, there is no information about the webs of the last species remaining in this genus, Wixia abdominalis O. Pickard-Cambridge, 1882. We observed that this spider builds complete orbs, but some individuals add a free-sector, remaining resting on a twig above the orb and holding a signaling thread. On the upper part of the orb the spiral distribution follows the pattern of increasing densities from the edge to the hub. However, on the lower part of orbs, this pattern is seen only in complete webs; in contrast, in webs with a free-sector the pattern of spiral distribution observed in lower part of webs is homogeneous from the edge to the hub. We discuss possible implications of the web structure of W. abdominalis for prey capture and how the incidental and functional hypotheses may explain the patterns of spiral spacing observed in this species.

Tengella perfuga Dahl, 1901 is a Nicaraguan cribellate zoropsid spider found in high altitude remnant cloud forest habitats bordering coffee plantations. Since its description in 1901, and its rediscovery in 2012, almost nothing is known of its natural history, life history, courtship or web spinning behavior. Observations were made in the field, as well as in the lab. Mature female T. perfuga occurred in funnel webs with several knockdown lines comprised of cribellate silk, and that were typically placed between buttress roots of strangler figs or other outcropping structures, while males abandoned their webs upon adulthood to search for females. Here, we describe the life history, growth, web ontogeny, courtship and reproductive behaviors, as well as silk use of this spider for the first time. There are 11–12 instars to reach adulthood and cribellate silk did not appear in juvenile webs until the eighth instar. Interestingly, orbicularian-like behaviors were observed in the initial appearance of cribellate silk lines in the juvenile web in a spiral-like pattern. Males exhibited positive allometric growth in Leg I from penultimate to adult instars, which likely plays an important role in courtship; this included strumming the sheet, stroking the female and depositing a thin ‘bridal veil' of silk on the female. Virgin females had ‘mating plugs' prior to exposure to males. This suggests that T. perfuga may be an interesting species with which to further examine sexual evolution and female choice.

Funnel webs are common and widespread taxonomically, but little is known about how they are built or details of their structure. Aglaoctenus castaneus (Mello-Leitão, 1942) (Lycosidae) builds horizontal, densely meshed funnel webs of non-adhesive silk, with a tangle of lines above. Web construction behavior was unique in that the spider frequently laid swaths of lines rather than simple drag lines, both to float bands of fine lines on the breeze as bridges to distant objects and to fill in the sheet. Spiders utilized special spinneret movements to widen the swaths of lines that they laid on sheets. These movements have not been seen in web construction by other araneomorphs, but are were similar to and perhaps evolutionarily derived from those used during prey wrapping by many other species. Observations, made with a compound microscope, of the construction behavior of the agelenid Melpomene sp. O.P. Cambridge 1898, and of lines and attachments in sheets of these species and another funnel web spider, the zoropsid Tengella radiata (Kulczyński, 1909) demonstrated the possibly general nature of including obstacles in the web. This probably disadvantageous behavior may be related to constraints in selecting web sites imposed by the need for sheltered retreats, or to the spider's inability to remove preliminary lines. The observation also showed the importance of further improvements in the discriminations made between “sheet” and “brushed” webs in recent discussions of spider web evolution.

Minor ampullate glands produce fibers that are involved in construction of the complex adhesive band for capturing prey, which is produced by particular cribellate spiders. Despite such a specific role, however, the glands persist even in species where production of cribellate capturing bands no longer occurs. In these species, minor ampullate fibers are instead used to reinforce major ampullate fibers in draglines and capturing webs. The fibers are also used in combination with the aciniform fibrils to make silk for bridging lines – airborne lines used by spiders to allow them to move to points on the substrate where these threads adhere. In this study, we compare the morphology of minor and major ampullate glands in related cribellate and ecribellate groups within spider families of the group traditionally termed the Amaurobioidea, which lies at the base of the RTA clade. We found that the minor ampullate glands are bifurcated in the cribellate members of this group, in particular in the representatives of the families Amaurobiidae, Titanoecidae, Desidae, Amphinectidae and Phyxelididae. In ecribellate representatives, the major ampullate glands are never bifurcated. We found irregularly branched minor ampullate glands in some representatives of the family Agelenidae. In other ecribellates, the glands are either unbranched or they are absent. Thus, bifurcation of the minor ampullate gland seems to be important in determining some aspect of cribellate capturing band formation that is as yet undetermined.

Eggs of black widow spiders in the genus Latrodectus Walckenaer, 1805 (Theridiidae) are known to be toxic when injected into mammals. We surveyed eggs from 39 species of spiders in 21 families to determine if spider egg toxicity is a unique property of widow spiders, or if spider egg toxicity is associated with other spider taxa. Eggs from 13 species of spiders in three families were determined to be highly lethal to mice, eggs from four species in four families were moderately lethal, and eggs from 22 species in 17 families lacked detectable lethality. Egg lethality appears to have evolved multiple times in spiders within the Araneidae, Theridiidae, and Agelenidae, and possibly also within the Tetragnathidae, Pimoidae, and Linyphiidae. These toxins in the various spiders may have differing chemical structures and could represent new sources of toxins that may be of future research interest.

Although spiders are common inhabitants of tree cavities, factors that drive their community structure in these microhabitats are little known. Here we investigated whether bark type, season, intraguild predation (IGP) among spiders, and presence of vertebrate predators can influence the spider community structure in tree cavities. We examined spider abundance and the taxonomic and functional composition of spiders in nest-boxes within two mixed forest stands in central Slovakia in 2012–2013. In total, 1211 spiders belonging to 31 species were sampled from 60 nest-boxes at two sites over three seasons. Spider abundance peaked in autumn as spiders sought wintering sites. Guilds and taxonomic composition changed seasonally with spring and autumn communities dominated by “Other hunters” (Anyphaenidae, Clubionidae, Philodromidae) while during summer the community was dominated by “Sheet web weavers” (Linyphiidae). The guild and taxonomic turnover may be partly explained by the interaction between spiders' phenology and IGP exerted by winter-active spiders on smaller spiders from autumn until spring. Bark type influenced the guild composition as dominance of “Space web weavers” was higher in trees with rough bark than in trees with smooth bark. The rough bark also reduced the intensity of IGP by Anyphaena accentuata (Sundevall, 1833) on philodromids. The presence of insectivorous birds reduced the abundance of spiders by 67%. The presence of bird predators altered the guild composition as they affected mostly the web spiders. The results show that the biotic interactions and abiotic factors interactively determined the spider community structure in the nest-boxes depending on spiders' functional traits.

Amblypygids (Order: Amblypygi) can be found across different habitat types, each with very different microhabitat structure, including rainforests, deserts, and caves in the tropics and subtropics. Most prior studies on amblypygid microhabitat use have focused on characteristics of trees and their relationship with amblypygid abundance, though many species regularly occupy refuges away from trees. Here we explore microhabitat use in the amblypygid Paraphrynus laevifrons Pocock, 1894 through mark-recapture surveys conducted along creeks and trails in a secondary forest in southeastern Costa Rica. We identified (1) microhabitat characteristics associated with abundance of P. laevifrons and (2) resighting ratio—the likelihood of finding individual P. laevifrons over multiple nights, potentially in association with a particular area (a putative territory). We measured four microhabitat characteristics: (i) number of visible refuges, (ii) surface area of vertical substrate, (iii) estimated plant cover of substrate, and (iv) presence/absence of an overhang. We found that the number of P. laevifrons sighted did not differ across wet and dry seasons, but P. laevifrons were sighted in greater numbers in creeks than trails. The abundance of P. laevifrons was positively affected by the presence of overhangs, there was no effect of plant cover, and the positive effect of number of refuges was stronger in trails, where overhangs were less common, than in creeks. Our results support earlier studies showing that amblypygids can be found more abundantly in areas with greater available refuges and potential shelter, suggesting that predation may be a strong source of selection on amblypygid microhabitat use.

Males of many species of spider engage in alternative mating tactics that do not involve pre-mating courtship. Here I report field observations of a novel opportunistic mating tactic of the wolf spider Rabidosa punctulata (Hentz, 1844): simultaneous double mating, whereby males that encounter copulating pairs also mount and achieve inseminations concurrently with the first male. On three separate occasions, female R. punctulata were observed mating with two males simultaneously. Males that mate with already copulating females likely receive multiple fitness benefits. It may allow courtship parasitism of other males while also reducing male agonistic interactions, eliminate the need to court or subdue the female, and reduce pre-mating cannibalism risk. If such behavior is common, it may limit sexual selection acting on male courtship displays by reducing the effectiveness of pre-mating female choice while also increasing sperm competition.

A bilateral gynandromorph specimen of the tarantula Pterinochilus murinus Pocock, 1897 is here described and illustrated. In addition, encounters with conspecific females were studied. The possible explanations for this case of gynandry are discussed. This constitutes the first formal report of gynandry in a mygalomorph spider.

The salticid spider Phidippus regius C.L. Koch, 1846 is documented preying on small frogs (Hyla spp., Osteopilus septentrionalis) and lizards (Anolis carolinensis and Anolis sagrei) in Florida, USA. Female as well as male P. regius were engaged in feeding on this type of vertebrate prey. A total of eight incidents of P. regius devouring vertebrates have been witnessed in seven Florida counties. Furthermore, we report an incident of a large unidentified Phidippus sp. (possibly P. bidentatus F. O. Pickard-Cambridge, 1901) preying on an immature anole lizard in Costa Rica. P. regius, otherwise known to feed almost exclusively on insects and spiders, is one of the world's largest salticid spiders reaching a maximum recorded body length of 2.2 cm. Most other salticid spiders appear to be too small in body size to overcome vertebrate prey. Vertebrate predation by salticid spiders has not been previously documented in the scientific literature. Together with Salticidae, spiders from 27 of 114 families (24%) are currently known to occasionally consume vertebrate prey.

Predation on earthworms is common in some generalist predator species, as for example several ground beetle species (Coleoptera: Carabidae) that frequently feed on earthworms. In spiders (Araneae), however, such behavior is far less well documented. A survey of reports on spiders feeding on earthworms yielded a total of 44 naturally occurring predation events. Spiders from 14 families were observed feeding on earthworms in nature, and species from two additional families consumed earthworm prey in captivity. Earthworm predation by spiders has been observed in temperate, subtropical, and tropical regions in 18 different countries. Tropical spiders from the families Theraphosidae (Mygalomorphae) and Ctenidae (Araneomorphae) accounted for 59% of the reported predation events. Reports from French Guiana document the capture of giant earthworms (0.6–1 m in length) by the giant tarantula, Theraphosa blondi (Latreille, 1804). Predation on giant earthworms by large tarantulas has also been observed in rainforest habitats in Brazil, Ecuador, Peru, and Venezuela. Wandering spiders (Ctenidae) are known to feed on earthworms in Belize, Brazil, Costa Rica, French Guiana, Guyana, and Singapore. Quite obviously, larger-sized mygalomorph and araneomorph spiders in humid tropical rainforests are predators with broad feeding niches—including earthworms and vertebrate prey in addition to arthropod prey—and this is presumed to improve the survival of these spiders. By comparison, reports of earthworm predation in temperate climate are rarer, and recent molecular studies of the diet composition of lycosid and linyphiid spider species in Swedish arable fields suggest that earthworms are not a common prey of these species.

Urbanization is associated with a variety of anthropogenic impacts that alter aquatic ecosystems and could affect riparian web-spinning spiders. The objective of this study was to evaluate how changes in web structural features and body condition of a horizontal orb-weaver are associated with surrounding levels of urbanization. Along an urban watershed in Puerto Rico, we found a significant negative relationship between the capture area of webs and in the body condition of spiders with increasing levels of surrounding impervious surface. We propose that these changes in web structure and body condition are associated with variations in the diversity and quality of prey, as well as the loss of riparian substrate in more heavily urban areas.