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Spiders in the subfamily Cyrtarachninae, including bolas spiders, are moth specialists, and it has been suggested that these spiders initiate web-weaving under high humidity. Here we used Pasilobus hupingensis to experimentally test whether Cyrtarachninae spiders build webs exclusively under high humidity. The results showed that humidity, as well as temperature and prey feeding history, affected web-building probability, but humidity had a much stronger effect. Moreover, spiders never constructed webs at under <70% humidity. We suggest that a mechanical property in sticky materials derived from moth specialization; namely, unusually high, yet rapidly degrading stickiness, is likely to have promoted the evolution of plastic foraging behaviour that varies with humidity. [ABSTRACT FROM AUTHOR]

Individuals may vary consistently in their architectural makeup of the constructions they build, which might have tremendous implications for their ecology and fitness. In particular, the relationship between individual differences in architectural constructions and behavior (i.e., animal personalities) is largely unexplored. Individual black widow spiders, Latrodectus hesperus, build a 3D cobweb made up of distinctive components serving to support foraging (gumfooted lines) or antipredator protection (structural lines). To explore the relationship between individual differences in behavior and architectural constructions, we quantified 1) the level of consistent individual variation in several elements of web structure and 2) the level of consistent individual variation in foraging behavior and its relationship with web structure. We controlled for condition-dependent or environmental effects by satiating all spiders prior to assays and maintaining them in standardized conditions. Spiders exhibited consistent differences in the number of gumfooted lines they built for capturing preys and overall web weight, but not in the number of structural lines. Individuals also varied consistently in their tendency to attack a prey cue, despite all spiders being satiated. Finally, spiders producing more gumfooted lines exhibited a higher tendency to attack the prey cue. Our results suggest that the architectural constructions may impact the expression of individual behavioral differences (or animal personalities) and suggest that individual behavior and extended phenotype may be part of alternative foraging strategies in L. hesperus. [ABSTRACT FROM AUTHOR]

Spiders in the Orbiculariae spin orb webs that dissipate the mechanical energy of their flying prey, bringing the insects to rest and retaining them long enough for the spider to attack and subdue their meals. Small prey are easily stopped by webs but provide little energetic gain. While larger prey offer substantial nourishment, they are also challenging to capture and can damage the web if they escape. We therefore hypothesized that spider orb webs exhibit properties that improve their probability of stopping larger insects while minimizing damage when the mechanical energy of those prey exceeds the web's capacity. Large insects are typically both heavier and faster flying than smaller prey, but speed plays a disproportionate role in determining total kinetic energy, so we predicted that orb webs may dissipate energy more effectively under faster impacts, independent of kinetic energy per se. We used high-speed video to visualize the impact of wooden pellets fired into orb webs to simulate prey strikes and tested how capture probability varied as a function of pellet size and speed. Capture probability was virtually nil above speeds of ~3 m s-1. However, successful captures do not directly measure the maximum possible energy dissipation by orb webs because these events include lower-energy impacts that may not significantly challenge orb web performance. Therefore, we also compared the total kinetic energy removed from projectiles that escaped orb webs by breaking through the silk, asking whether more energy was removed at faster speeds. Over a range of speeds relevant to insect flight, the amount of energy absorbed by orb webs increases with the speed of prey (i.e. the rates at which webs are stretched). Orb webs therefore respond to faster - and hence higher kinetic energy - prey with better performance, suggesting adaptation to capture larger and faster flying insect prey. This speed-dependent toughness of a complex structure suggests the utility of the intrinsic toughness of spider silk and/or features of the macro-design of webs for high-velocity industrial or military applications, such as ballistic energy absorption. [ABSTRACT FROM AUTHOR]

Nearly all social spiders spin prey-capture webs, and many of the benefits proposed for sociality in spiders, such as cooperative prey capture and reduced silk costs, appear to depend on a mutually shared web. The social huntsman spider, Delena cancerides (Sparassidae), forms colonies under bark with no capture web, yet these spiders remain in tightly associated, long-lasting groups. To investigate how the absence of the web may or may not constrain social evolution in spiders, we observed D. cancerides colonies in the field and laboratory for possible cooperative defense and foraging benefits. We observed spiders' responses to three types of potential predators and to prey that were introduced into retreats. We recorded all natural prey capture over 447 h both inside and outside the retreats of field colonies. The colony's sole adult female was the primary defender of the colony and captured most prey introduced into the retreat. She shared prey with younger juveniles about half the time but never with older subadults. Spiders of all ages individually captured and consumed the vast majority of prey outside the retreat. Young spiders benefited directly from maternal defense and prey sharing in the retreat. However, active cooperation was rare, and older spiders gained no foraging benefit by remaining in their natal colony. D. cancerides does not share many of the benefits of group living described in other web-building social spiders. We discuss other reasons why this species has evolved group living. [ABSTRACT FROM AUTHOR]

There is controversy about the function of silk stabilimenta, also called silk decorations, on spiders' webs. Most of the proposed hypotheses have been tested using indirect methods. Protection against predators, advertisement for vertebrates to avoid web damage, and increasing prey attraction are the most popular hypotheses. In this study, I tested the prey attraction hypothesis on the silk decorations of the araneid Argiope savignyi using a trial tunnel built in the field, in which I exposed stingless bees Telragonisca angustula to decorated and undecorated webs placed on wooden frames. I carried out two experiments: 1) a three- frame choice, consisting of a frame bearing a decorated web, one bearing an undecorated web and a control frame without web and spider; 2) a two-frame choice, in which the bees were exposed to only two frames consisting of "decorated web vs. control," "decorated web vs. undecorated web," and "undecorated web vs. control". In favor of the prey attraction function, I found that decorated webs intercepted more bees than webs deprived of the decoration or controls with no webs. Argiope savignyi's decorations might lure prey to the web by UV-reflectance as it has been suggested for other Argiope species. [ABSTRACT FROM AUTHOR]

Animals use behavioural plasticity to cope with conflicting selective pressures. We investigated how prey availability affects the spinning of cobwebs, whose architecture influences both prey capture and defence. Fed western black widows spun cobwebs containing more silk than did fasted spiders. However, fed spiders invested relatively less silk in the sheets and sticky gumfooted threads of webs and relatively more silk in supporting threads than did fasted spiders. The material properties of silk spun by fed and fasted spiders were relatively similar, but silk threads spun by fed spiders were twice as thick as those of fasted spiders, increasing web strength by 225%. Finally, spiders fed late in the experiment did not reproduce, even though they received the same amount of food as spiders fed earlier, 43% of which reproduced. The reallocation of silk in cobwebs away from sheets and sticky gumfooted threads, which function in prey capture, to supporting threads, which surround spiders with defensive clouds of silk, is consistent with reduced foraging effort and increased predation risk avoidance by fed spiders. Furthermore, this behavioural shift occurs as spiders are reproducing, when spiders can most afford the costs of reduced prey capture and would most benefit from enhanced protection. Our results contrast with those of previous studies on orb-weaving spiders, which found reductions in the sizes of webs as spiders caught more food. Thus, the architectures of spider webs reflect many selective pressures, the effects of which may vary with physiological state. [Copyright &y& Elsevier]