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Web Orientation in the Spider Micrathena Gracilis (Araneae: Araneidae)
Ecology
Abstract
Web orientation (direction that spiders faced) in a forest-dwelling orb web-building spider, Micrathena gracilis (Araneidae), was related to the microhabitat where webs are constructed. Individuals in shaded (closed) microhabitats faced predominantly north/south, while those in well-lighted microhabitats (open and patchy) faced east/west. Several variables were examined in an effort to explain the patterns that emerged. Wind speeds were found to be so low within the interior of the forest that available instrumentation could not measure them. Nethertheless, webs were not aligned with prevailing winds. There were no significant differences in web site parameters (height, bridge thread distance) between microhabitats. Artificial web studies indicate that prey abundance is greater in open microhabitats and at lower heights, though prey movement through all microhabitats is nondirectional. Spider body temperature, however, was positively correlated with the amount of solar radiation striking the animal, which varied with both microhabitat and direction of orientation. The compass orientation of a spider's web influenced the amount of radiation to which the spider was exposed, and thus affected its body temperature. A model is proposed that relates the time an individual spider can spend on its web to the amount of heat accrued by the spider. Both too little or excessive body heat might affect activity. Since time on the web is positively correlated with total prey captured, more time spent on the web effectively increases the availability of prey. Web orientation is suggested as a behavioral thermoregulatory mechanism which allows Micrathena gracilis enough flexibility to exploit a variety of microhabitats and to maximize its time on the web, thus optimizing its prey take in each habitat.
... One explanation for this discrepancy is that in this population the species constructs the web with the dorsal body section directed towards open space (Messas et al. 2021), instead of towards the vegetation (as we found). This variation might be linked to local differences in light and wind direction, factors that can determine how spiders orient their body on the web (Robinson and Robinson 1978;Biere and Uetz 1981;Herberstein and Heiling 2001). In fact, the way spiders position their body on the hub varies among species (Nakata and Zschokke 2010;Rao et al. 2011;White et al. 2017) and may be related to prey attraction (Rao et al. 2015;Peng et al. 2020) or to other factors like thermoregulation (Biere and Uetz 1981;Herberstein and Heiling 2001;Rao and Mendoza-Cuenca 2016). ...
... This variation might be linked to local differences in light and wind direction, factors that can determine how spiders orient their body on the web (Robinson and Robinson 1978;Biere and Uetz 1981;Herberstein and Heiling 2001). In fact, the way spiders position their body on the hub varies among species (Nakata and Zschokke 2010;Rao et al. 2011;White et al. 2017) and may be related to prey attraction (Rao et al. 2015;Peng et al. 2020) or to other factors like thermoregulation (Biere and Uetz 1981;Herberstein and Heiling 2001;Rao and Mendoza-Cuenca 2016). Identifying the variables that determine G. cancriformis position preference on the web is still an open question and needs to be tested under controlled conditions. ...
Colour has been hypothesized to play a crucial role in prey capture for sit-and-wait predators that rely on visual cues to deceive their prey. Prey capture success has been directly linked to colouration in spiders; however, evidence so far focuses mostly on dorsal colouration, excluding ventral patterns that are visible to prey and may be relevant for prey attraction. Here, we explored whether the dorsal and ventral colouration of a colour polymorphic spider is associated with light environment and prey capture success. We quantified the number of prey captured across three dorsal (black, white, and yellow) and two ventral (black and a mosaic yellow/orange pattern) morphs of Gasteracantha cancriformis, considering light intensity on dorsal and ventral sides. We found that spiders capture more prey in low light environments, and that individuals often expose their dorsal colouration towards low light levels. We did not find significant differences in prey capture rate between morphs dorsally or ventrally. These results indicate that how and where spiders position their web can be more important for prey capture than colouration. Alternative hypotheses such as aposematism, camouflage and thermoregulation deserve more attention in future studies that aim to understand the role of colouration in spiders and the factors causing spider colour polymorphisms.
... Solitary wasps and bees are known to forage at long distances away from their nests (a maximum of 1,200 m away for Xylocopa violacea (Molitor), a solitary bee in a similar size range as S. caementarium and C. californicum; reviewed in Gathmann and Tscharntke [2002]). Only two of our field sites had deciduous forest patches (preferred habitat for M. gracilis as per Biere and Uetz [1981], Hodge [1987]) that were within this maximum foraging distance, given the predominance of open agricultural landscape surrounding Lincoln, NE. ...
... In contrast to the potentially heat-seeking wasps, M. gracilis are most commonly found in shaded areas within deciduous forests (Biere and Uetz 1981). In fact, female M. gracilis will actively move from habitat types with higher sun exposure to more shaded areas (Hodge 1987). ...
Predator diets represent a potential interaction between local prey availability, prey antipredator defenses, and predator foraging behavior. Female spider-specialist mud-dauber wasps (Hymenoptera: Sphecidae) collect spiders and provision them intact, but paralyzed, to their developing larvae, providing a unique means of quantifying the diversity and abundance of prey that they capture. Mud-dauber wasps are hypothesized to be a major source of selection on antipredator defenses in web-building spiders, and the spiny and thickened abdomens of female spiny orb-weaving spiders (Araneae: Araneidae) are hypothesized to function as antiwasp defenses. We inventoried spider prey from nests of the mud-dauber wasps Sceliphron caementarium (Drury) and Chalybion californicum (Saussure), and surveyed for spider fauna in areas surrounding nest collection sites, to specifically investigate if the spiny orb-weaver Micrathena gracilis (Walckenaer) was collected as prey by these wasps. We collected nests from six sites in southeastern Nebraska from two regions that we classify based on habitat—a forest corridor and agricultural land. We collected 761 intact spider prey from 87 nests and identified them to the family level. None of these spiders were M. gracilis. Micrathena gracilis were rare in faunal surveys on agricultural land and, surprisingly, absent in forest corridor surveys. Mud-dauber wasps were more common; we collected more spiders on agricultural land than in the forest corridor. We propose that in agricultural landscapes, the lack of certain spiders in mud-dauber wasp nests is driven by habitat use differences between predators and prey rather than physical antipredator defenses.
... Isto ocorre em razão de que grande parte das presas voe nessa faixa de altura, além dessas teias poderem ser utilizadas como local de pouso e descanso das presas, bem como pelo fato de que muitas presas caem do sub-bosque, assim, teias mais baixas devem receber mais quedas de presas (Waldorf 1976). Entretanto, estudos demonstram que a altura das teias pode variar ao longo do ano, estando isso relacionado com vários fatores além da captura de presas, tais como distúrbios ambientais e variação do microclima (Biere & Uetz 1981;Hodge 1987;Herberstein 1997). Desse modo, o presente trabalho deve ser considerado para a época do ano em que foi realizado (primavera, em outubro) e estudos futuros podem responder se o padrão de construção de teias, bem como sua eficiência, é modulado pelas variações sazonais. ...
... While pitfall trapping suggests that alfalfa perimeter strips did not impact the most common ground-dwelling arthropods in this study, sticky traps in trap cropped plots captured signi cantly more spiders than those in control plots. Vegetation structure in uences microhabitat availability and utilization by spiders (Biere and Uetz, 1981;Biwas, 2015), and these data suggest that alfalfa perimeter strips increase the abundance of canopy-dwelling more than ground-dwelling spiders. Overall, these data suggest that incorporating alfalfa perimeter strips into strawberry eld design has limited effects on the bene cial arthropod community. ...
Lygus lineolaris Palisot de Beauvois (Hemiptera: Miridae) is the primary insect pest of strawberry in eastern and central North America. Strategies to minimize L. lineolaris colonization of strawberry at bloom and peak fruit susceptibility without impacting pollinator health must be developed. To this end, we examined the potential of alfalfa perimeter strips to reduce L. lineolaris populations in June-bearing strawberry fields. Over a three-year experiment, L. lineolaris densities and beneficial arthropod abundance were monitored on three commercial strawberry farms where alfalfa was established as a trap crop near strawberry plots. Alfalfa perimeter strips were found to concentrate L. lineolaris populations and led to a 36% reduction in L. lineolaris densities in adjacent strawberry plots compared to controls. When a protein immunomark-capture experiment was conducted to examine the extent of movement between the alfalfa strips and adjacent strawberry plots, it was determined that approximately three times as many L. lineolaris migrated from strawberry to alfalfa than vice versa. Moreover, adult females were overrepresented among immigrants to alfalfa, suggesting that alfalfa may be a preferred oviposition site for L. lineolaris . While the presence of alfalfa perimeter strips increased beneficial arthropod abundance and diversity in experimental plots overall, most effects were limited to the alfalfa strip itself, with little spillover into adjacent strawberry plots. These data suggest that preferential utilization of alfalfa by L. lineolaris underlies the observed population reductions and that alfalfa perimeter strips act as a trap crop in June-bearing strawberries.
... ese microhabitats are known to provide architectural support for brood care, mating, and shelter [19]. Microhabitats also provide climatic variables, such as wind direction, moisture, and temperature [52]. ...
Spiders (Arachnida, Araneae) represent one of the largest groups of organisms on Earth with more than 45,000 recorded species found in nearly all terrestrial communities. In these communities, spiders are obligate predators and generalist consumers regulating the density of pests. Spiders have a stupefying array of prey hunting strategies ranging from ambushing to the use of complex silk nares. Spider silk is incredibly tough and can be used for many applications such as wrapping and immobilization, catching prey, as dragline to connect spiders to the web, as ballooning to aid dispersal of juveniles, as shelters in burrows, for mating, and as egg sacs (or cocoons). Typically, spider egg sacs are multilayered, complex structures that physically protect the eggs and hatchlings against parasitoids, predators as well as changing temperatures. Much research has been undertaken to elucidate the ecological role of spiders and the mechanical characteristics of silks. However, few studies have examined the parental care of spiders and the role of egg sacs. This review goes into great detail about spider parental care and the functions of egg sacs.
... This trend is even more evident for pastures (PA), which depicted the lowest values of HLD and HLF, which might result from their continuous disturbance patterns (fire, cattle) and low complexitydominated by herbaceous vegetation (mainly species of the genus Brachiaria spp.) used for extensive livestock farming (Table S1 in Supplementary Material) [71]. These are especially unfavorable conditions for RFU web spiders, which are associated with the reduced diversity of arthropods, hiding places, and microclimates, which disrupt mating behaviors as well as inter-and intraspecific competition [77][78][79][80]. ...
Spiders have been increasingly used as environmental and ecological indicators in conservation and ecosystem management. In the Neotropics, there is a shortage of information regarding spiders’ taxonomies and ecological responses to anthropogenic disturbances. To unravel these hitches, we tested the possibility of using high-level diversity and high-level functionality indicators to evaluate spider assemblages’ sensitivity to landscape changes. This approach, if proven informative, might overcome the relevant limitations of taxonomic derived indexes, which are considered time-consuming, cost-demanding and dependent on the (few) expert taxonomists’ availability. Our results highlight the pertinence of both indicators’ responses to the structural changes induced by increasing anthropogenic disturbance, and are associated with reductions in ecosystem complexity, microclimates, and microhabitats. Overall, both indicators were sensitive to structural changes induced by anthropogenic disturbance and should be considered a useful resource for assessing the extent of ecosystems’ disruptions in the Neotropics, and also to guide managers in landscapes’ restoration.
Lygus lineolaris Palisot de Beauvois (Hemiptera: Miridae) is the primary insect pest of strawberry in eastern and central North America. Strategies to minimize L. lineolaris colonization of strawberry at bloom and peak fruit susceptibility without impacting pollinator health must be developed. To this end, we examined the potential of alfalfa perimeter strips to reduce L. lineolaris populations in June-bearing strawberry fields. Over a three-year experiment, L. lineolaris densities and beneficial arthropod abundance were monitored in commercial strawberry fields with and without alfalfa perimeter strips. Alfalfa perimeter strips were found to concentrate L. lineolaris populations and led to a 36% reduction in L. lineolaris densities in adjacent strawberry plots compared to controls. When a protein immunomark-capture experiment was conducted to examine the extent of movement between the alfalfa strips and adjacent strawberry plots, it was determined that approximately three times as many L. lineolaris migrated from strawberry to alfalfa than vice versa. Moreover, adult females were overrepresented among immigrants to alfalfa, suggesting that alfalfa may be a preferred oviposition site for L. lineolaris. While the presence of alfalfa perimeter strips increased beneficial arthropod abundance and diversity in experimental plots overall, these increases were limited to the alfalfa itself, with little spillover into adjacent strawberry plots. These data suggest that preferential utilization of alfalfa by L. lineolaris underlies the observed population reductions and that alfalfa acts as a trap crop in June-bearing strawberries.
To successfully capture flying insect prey a spider's orb web must withstand the energy of impact without the silk breaking. In this study we examine the anchor threads: the silk lines that anchor the main capture area of the web to the surrounding environment. These anchor threads can account for a large portion of the web, yet are usually excluded from experiments and simulations. We compared projectile capture and kinetic energy absorption between webs with and without access to anchor threads. Webs with anchor threads captured significantly more projectiles and absorbed significantly more energy than those with constrained anchors. This is likely because the anchor threads increase web compliance, resulting in webs with the ability to catch high-energy flying insects without breaking. Anchor threads are one example of how different types of web architecture expand the range of possible prey capture by enabling the web to withstand greater impacts.
Animals that create structures often display non-random patterns in the direction of their constructions. This tendency of oriented construction is widely presumed to be an adaptive trait of the constructor’s extended phenotype, but there is little empirical support for this hypothesis. Particularly, for cavity nesting-birds there is a lack of studies examining this issue. In this study of a primary cavity excavator, the endangered red-cockaded woodpecker ( Dryobates borealis ), we show that cavity entrances exhibited a strong westward bias in all 11 of the populations examined throughout the geographic range of the species in the southeastern United States. This species requires cavities in living pine trees for roosting and nesting that often take many years to complete, resulting in many incomplete excavations on the landscape. We used population monitoring data to show that orientation was stronger among completed cavities than incomplete cavities. There was a significant correlation between latitude and average cavity direction among populations, turning northward with increasing latitude, suggesting adaptation to local conditions. Long-term monitoring data showed that cavity orientation and breeding group size are correlated with egg hatching rates, fledging rates, and the total number of fledglings produced per nest. Our results provide empirical evidence from extensive long-term data that directional orientation in animal constructions is an important feature of the extended animal phenotype and have immediate implications for animal ecology and the conservation of endangered species.
Temperature affects nearly all of life's processes. Ectothermic animals living in temperate regions are subjected to dramatic daily shifts in temperature that force them to adapt in a variety of ways. The Dotted Wolf Spider (Rabidosa punctulata) mates during fall, which leaves this species vulnerable to temperature swings that can impact their reproductive success. In this study, we manipulated temperature in a controlled laboratory experiment to examine how the mating behaviors of both sexes of R. punctulata are affected in cold (4.4C) and warm (26.74C) environments. Overall, the species seems well acclimated to colder environments. While these spiders were slower to begin moving in the cold, they spent an equal percentage of the trial in motion across both temperature treatments. Males were less likely to adopt any mating behaviors in the cold, and overall pairs were significantly less likely to mate in the cold. However, males were able to successfully mount and at least two males were able to copulate in the near freezing temperatures. Directly mounting females without prior courtship was the most successful mating tactic regardless of temperature, and there was a trend suggesting males were more likely to forgo courtship and use direct mounting when interacting with females in the cold. This study highlights the amazing flexibility in reproductive tactics that enable mating success in R. punctulata despite experiencing cold temperatures in their fall mating season.
Analyses of the movements and web-site characteristics of the desert spider Agelenopsis aperta (Gertsch) demonstrate that web locations offering the following habitat features are actively selected: shrubs, depressions, litter, and flowering herbs. A model of the effects of the thermal environment and prey avalability on the reproductive success of spiders occupying various web-site types is developed. The estimated productivity for an excel- lent web site (grassland depression with attractants) is 13X that determined for a poor site (lava surface). Model results suggest that more energy is to be obtained from selection of a favorable thermal environment (eight-fold difference) than from a site offering greater num- bers of prey (two-fold difference). The presence of flowers at web sites increases the prob- ability of receiving an occasional high prey density, whereas litter and habitat features pro- viding shade (shrubs and depressions) allow increased spider activity through limitation of body temperature.
1. Seventy-one species of spider were recorded from the Moor House National Nature Reserve, and the family structure of this fauna followed a sub-arctic pattern. 2. Both the common species of orb-web spinning spiders, Meta merianae and Araneus cornutus were restricted in their distribution to breaks in the blanket bog cover. This appeared to be due to the architecture of the site and not to the availability of prey or the effect of wind. Meta merianae was found mainly under peat overhangs, whilst Araneus cornutus occurred on the tips of Calluna shoots and on Juncus effusus. This difference in distribution was attributed primarily to their different light reactions, rather than directly to humidity requirements. 3. Pitfall traps showed four species of Lycosidae to possess a degree of habitat specificity which could be detected on a microdistribution plot only 74.4 m2 in extent. Their distribution was related to the ability of the species to withstand desiccation, and population estimates of the number of Pirata piraticus males on a 74.4 m2 plot were made. 4. The Linyphiidae showed marked habitat specificity in eight vegetation types, and their numbers (and biomass) were correlated with the numbers of other arthropods available on the sites. Spider densities in these areas are compared with those obtained by other workers. Aggregations occurred in patchy Calluna/Eriophorum vegetation, and in an unevenly grazed alluvial grassland, high numbers of spiders were found only in the tussocks. Coarse vegetation, resulting from the withdrawal of grazing pressure by sheep, supported larger numbers of individuals and species of spider. Stratification of species was detected in a stand of Calluna/Eriophorum vegetation by an examination of web positions.
(1) A structurally simple limestone pavement habitat is distinguished from a more complex Calluna vulgaris/Vaccinium myrtillus habitat at 350 m near Ingleborough Hill (Yorkshire West Riding). (2) The population density and distribution of the argiopid spider Araneus diadematus were studied by visual counting and web measurement. (3) The population density varied from 1.33/m2 in June to 0.12/m2 in September. This species is strikingly concentrated in the limestone grikes. (4) The success rate of spiders transferred to the Calluna areas was low, but could be improved by transferring the animals on wooden frames or by cutting spaces 50 cm wide by 10 cm deep in the heather. Araneus survived better in the heather microclimate. (5) Few Araneus webs were found in grikes wider than 40 cm or narrower than 10 cm. The orb diameters and bridge thread lengths measured in the field were found to be independent. (6) When the spatial nature of a grike was changed, the pattern of web distribution changed. Creating an artificially high Araneus density in a grike produced a rapid drop in density, but the final value was higher than normal, and it is concluded that there is no severe competition for spaces in the grikes. (7) The possible reasons for the lack of Araneus of all ages in the Calluna areas are discussed. It is suggested that habitat structure can act both through space available and support stability and these can affect both the bridge thread and the final orb-web. (8) It may be worthwhile to pay more attention to habitat architecture in studies involving invertebrate micro-distribution.
A field study of the ecology and natural history of the spider, Nephila clavipes, was conducted between May 1972 and September 1973. The habitat of Nephila clavipes on the Texas Coastal Plain is described, as well as its life cycle, monthly variation in selected web parameters, and abundance in a study area. Height of the web aboveground, magnetic orientation, degree of slant, and density of weblines all exhibited consistent changes during the year. Numerical density of the spiders was approximately constant during the year, suggesting that adult female Nephila are relatively immune to predation and that there are only a finite number of suitable web sites within the study area.
The influence of thermal stress on the population dynamics of Argiope trifasciata Forskål, a diurnal orb-weaving spider, was studied in the southeastern United States. Comparison of laboratory determined thermal tolerances (48.9°C to 58.6°C for second through tenth instars) and spider body temperatures modeled under field conditions in 1975 indicated that A. trifasciata did not experience mortality from thermal overloading. Vertical orientation of spiders on their webs exposed the minimum body area of the spider to direct solar insolation during mid-day. This orientation and silver body coloration probably helped reduce body temperatures below lethal temperatures. A behavioral correlate of sublethal stress, non-random web orientation, was exhibited on 1 Aug and 14 Aug by spiders occupying all types of habitats. This is the time period when spider body temperatures were closest to laboratory-determined thermal tolerance maxima. Web orientations at these times exposed less surface area of the spiders to the sun. Web orientations became non-random again in Oct, this time resulting in maximum exposure of the spiders to the sun. The venter (underside of the abdomen) changed with maturity morphologically from silver to black, and was oriented toward the sun (SW to SE). /// Исследаваки влияние теплового стресса на динамику популяции Argiope trifasciata, дневного паука, плетущего сферическую сеть, на юге-востоке США. Сравнение температурной устойчивости в лабораторных условнях (от 48.9°C до 58.6°C у 11-х возрастов) и температуры тела пауков в полевых условиях, проведенные в 1975 г., показали, что A. trifasciata не погибают от перегрева. Вертикальная ориентатсия паука на сети обеспечивает освещенность прямыми лучами минимальной площади тела в полуденные часы. Такая ориентация и серебристая окраска очевидно способствуют снижению температуры тела ниже леталвной границы. Пведение при сублетальных стрессах ниеслучайная ориентация сетей навлюдалась 1 и 14 августа у пауков во всех типах местообитаний. Это-период, когда температура тела пауков была близка к измеренному в лаборатории максимуму термальной толерантности. Ориентация сети в этих случаях отрывает незначительную часть поверхности тела пауков солнечным лучам. Ориентация сети снова оказывается неслучайной в октябре, но на этот раз экспонируется максимум поверхности тела паука. Брюшко изменяет окрахку от серебрнитой до черной по достижении половой зрелост и ориентировано на солнце от юго-запада на юго-восток.
1. The floor-dwelling harvestmen are associated primarily with woodland, and the vertical migration which has been described for some of these species is not an exodus from the ground but an upward spread. 2. Although harvestmen are active throughout the 24 h, most movement is at night. When hungry, harvestmen may be active during the day if the humidity is high, and this combination of factors occurs more often in the scrab than in the wood. 3. The cursorial arachnids demonstrate the ecological similarity between winter and night, and between summer and day, and seasonal and diurnal periodicities are discussed in this context. 4. It is suggested as a general rule that the diurnal periodicity of a species is most clearly marked in the most favourable environment. 5. The seasonal variation in spider activity is much greater in the scrub than the wood, as the spider fauna of the scrub is dominated by the Lycosidae and a few species of Linyphaeidae. 6. The Linyphaeidae in the wood give a succession of specific activity peaks which reduces the seasonal variation, and, on this evidence, a graphical model is presented to explain the correlation between the aperiodicity and the complexity of a community.
Solar radiation was measured within and above an east Tennessee deciduous forest over a 2-yr period. Diurnal patterns of within-forest radiation follow the temporal variation in incident radiation but become more irregular with depth in the forest because of the highly variable penetration of beam radiation in space and in time. Seasonally, radiation in the forest increases substantially from winter to its annual maximum in early spring as solar elevations increase. Although solar elevations continue to rise each day until the summer solstice, amounts of total radiation and its beam component drop sharply in the forest with the advent of leaf expansion. Diffuse radiation in the forest continues to increase slowly following the onset of leaf expansion but reverses as the forest approaches a fully leafed state. Following the summer solstice, forest structure remains essentially static until abscission while solar elevations decrease. In summer and early autumn, total radiation and both its beam and diffuse components decrease slowly in the forest to their annual minimum in autumn. With leaf abscission and subsequent fall, radiation increases slightly in the forest but soon declines again as solar elevations approach their annual minimum of the winter solstice.
The energy costs of the predation strategy of the web-spinning spider Lypthyphantes zimmermanni were investigated in the laboratory. The standard respiratory costs associated with the stationary aspect of the strategy were estimated by means of a Gilson respirometer run at the different temperatures prevailing month by month in the beech woodland litter layer which comprises the spider's natural habitat. Respiration rate is related to weight by an exponent with a mean value of 0.7398. The Q
10 of respiration rate is 2.41 between 5C and 10C and 1.97 between 10C and 15C. The energy costs of producing a web comprise the active respiratory costs associated with the locomotory activity involved in spinning a web together with the energy value of the silk used in the web manufacture. The former were evaluated by allowing a spider to spin a web in a respirometer, subtracting the calculated standard respiratory energy costs for a spider of equivalent weight and multiplying by a correction factor for web size. The relationship between spider weight and area of web produced was established in the laboratory. The respiratory cost of spinning a web is effectively constant with temperature at 724.4610-3 J for an adult (4 mg) spider. The energy value of spider silk was estimated by means of a bomb calorimeter and found to be 17,435 J g-1. The energy content of the silk of a single adult's web is 1.16 J, giving energy cost of web production of 1.88 J at all temperatures.
1.1. The cost of web-building and the standard metabolism of a sheet web-building wolf spider, Sosippus janus Brady, were measured at 25°C.2.2. The cost of activity is about 18% of the total cost of the web, the remainder being web silk cost.3.3. The cost of activity in sheet web-building was compared with a literature value for an orb-weaver and found to be similar. An average value is proposed as useful in estimating the cost of activity for other species of web-building spiders, given the weight of the web.