Species Of Orb-weaving Spiders Research Articles

Adhesive contact and protein elastic modulus tune orb weaving spider glue droplet biomechanics to habitat humidity

Tiny glue droplets along the viscous capture threads of spider orb webs prevent insects from escaping. Each droplet is formed of a protein core surrounded by a hygroscopic aqueous layer, which cause the droplet's adhesion to change with humidity. As an insect struggles to escape the web, a thread's viscoelastic core proteins extend, transferring adhesive forces to the thread's support fibers. Maximum adhesive force is achieved when absorbed atmospheric moisture allows a flattened droplet to establish sufficient adhesive contact while maintaining the core protein cohesion necessary for force transfer. We examined the relationship between these droplet properties and adhesive force and the work of extending droplets at five relative humidities in twelve species that occupy habitats which have different humidities. A regression analysis that included both flattened droplet area and core protein elastic modulus described droplet adhesion, but the model was degraded when core protein area was substituted for droplet. Species from low humidity habitats expressed greater adhesion at lower humidities, whereas species from high humidity habitats expressed greater adhesion at high humidities. Our results suggest a general model of droplet adhesion with two adhesion peaks, one for low humidity species, which occurs when increasing droplet area and decreasing protein cohesion intersect, and another for high humidity species, which occurs when area and cohesion have diverged maximally. These dual peaks in adhesive force explain why some species from intermediate and high humidity habitats express high adhesion at several humidities. Statement of significanceWe characterized the effect of humidity on the adhesion of twelve orb weaving spider species’ glue droplets and showed how humidity-mediated changes in the contact area of a droplet’s outer, hygroscopic aqueous layer and the stiffness of its protein core affect droplet performance. This revealed how droplet adhesion has been tuned to the humidity of a species’ habitat and allowed us to revise a model that describes the environmental determinants of droplet biomechanics.

Two New Species of Orb-Weaving Spiders of the Genera Cyrtarachne Thorell, 1868 and Pasilobus Simon, 1895 (Araneae: Araneidae) from India

Two new species of orb-weaving spiders, Cyrtarachne wayanadensis sp. nov. and Pasilobus sahyadriensis sp. nov., are recorded from Southern Western Ghats, Kerala. Detailed description and illustrations of the new species are provided.

Ocrepeira klamt sp. n. (Araneae: Araneidae), a novel spider species from an Andean páramo in Colombia.

Herein we describe Ocrepeira klamt sp. n. (Araneae: Araneidae), a new orb-weaving spider species from a Colombian páramo, which was formerly inaccessible for scientific studies due to decades long armed conflicts. Both, phenotypic and molecular data are used to confirm genus affiliation, and the new species is placed into phylogenetic context with other araneid spiders. Morphological characteristics and ecological notes of Ocrepeira klamt sp. n. are reported together with the sequence of the barcoding region of cytochrome c oxidase subunit I (COI) to provide a comprehensive description of the spider, facilitating future identification beyond taxonomic experts. With this study we contribute to the taxonomic knowledge that is required to inventory the hyper diverse yet threatened ecosystem of the Colombian páramos.

Different patterns of behavioral variation across and within species of spiders with differing degrees of urbanization

Behavioral characteristics importantly shape an animals’ ability to adapt to changing conditions. The notion that behavioral flexibility facilitates exploitation of urban environments has received mixed support, but recent studies propose that between-individual differences are important. We leverage existing knowledge on three species of orb-web spider (Araneidae, Araneae) whose abundances differ along an urban–rural gradient to test predictions about between- and within-species/individual behavioral variation. We sampled Larinioides sclopetarius from their urban environment, and two species from suburban environments, Zygiella x-notata and Nuctenea umbratica. For each species, we quantified activity in a novel environment and within-species aggression. We analyzed between- and within-individual variation in behavior as well as their repeatability and correlations. As predicted, L. sclopetarius exhibited the highest activity in a novel environment and N. umbratica the lowest. Across all species, males were more aggressive than females and Z. x-notata was the most aggressive, followed by L. sclopetarius and N. umbratica. For all species, between-individual differences in activity and aggressiveness were repeatable; but the two behaviors were not correlated for any species. We next tested how group composition in relation to aggressiveness affects survival in high density conditions. Groups of Z. x-notata consisting of aggressive and tolerant spiders had higher survival rates than groups composed of only aggressive or tolerant individuals. Ultimately, we uncovered a complex pattern of behavioral variation between species as well as between and within individuals and we discuss the relative roles of this variation with respect to adapting to urban environments. Urbanization has drastically changed biodiversity patterns. While the majority of species cope poorly with urban habitats, some species flourish in cities. Our understanding of behavioral characteristics that facilitate this exploitation, however, remains poor. We explored between and within species and individual variation in behaviors in ecologically similar orb-weaving spider species whose abundances differ along the urban–rural gradient. We detect both consistent individual differences and plasticity, in individuals’ response to a novel environment, suggesting that some degree of flexibility in reaction to novelty may be crucial in an urbanized environment. We also found that variation in aggressiveness type enables survival in high density conditions, conditions typical for urban populations. Urban populations thus exhibit a complex pattern of behavioral flexibility and behavioral stability.

Two new species of orb-weaving spiders of the genus Larinia (Araneae, Araneidae) in meridional Brazil.

The araneid genus Larinia Simon currently includes 56 species, eleven of them with New World distribution (World Spider Catalog, 2016). North American species of the genus were revised first time by Levi (1975) and South American species by Harrod et al. (1991). According to these authors there are four species known from subtropical South America (Larinia bivittata Keyserling 1885; L. montecarlo (Levi, 1988); L. t-notata (Tullgren, 1905); L. tucuman Harrod, Levi & Leibensperger, 1991) and also four species known from tropical South America (L. ambo Harrod, Levi & Leibensperger, 1991; L. directa (Hentz, 1847); L. lampa Harrod, Levi & Leibensperger, 1991; L. neblina Harrod, Levi & Leibensperger, 1991). According to Buckup et al. (2010) a total of 209 species of Araneidae are recorded for state of Rio Grande do Sul, including the three species L. bivittata, L. montecarlo and L. t-notata.

Reproducing Natural Spider Silks’ Copolymer Behavior in Synthetic Silk Mimics

Dragline silk from orb-weaving spiders is a copolymer of two large proteins, major ampullate spidroin 1 (MaSp1) and 2 (MaSp2). The ratio of these proteins is known to have a large variation across different species of orb-weaving spiders. NMR results from gland material of two different species of spiders, N. clavipes and A. aurantia , indicates that MaSp1 proteins are more easily formed into β-sheet nanostructures, while MaSp2 proteins form random coil and helical structures. To test if this behavior of natural silk proteins could be reproduced by recombinantly produced spider silk mimic protein, recombinant MaSp1/MaSp2 mixed fibers as well as chimeric silk fibers from MaSp1 and MaSp2 sequences in a single protein were produced based on the variable ratio and conserved motifs of MaSp1 and MaSp2 in native silk fiber. Mechanical properties, solid-state NMR, and XRD results of tested synthetic fibers indicate the differing roles of MaSp1 and MaSp2 in the fiber and verify the importance of postspin stretching treatment in helping the fiber to form the proper spatial structure.

Systematic review of a new orb-weaving spider genus (Araneae: Araneidae), with special reference to the Australasian-Pacific and South-East Asian fauna

The Australasian-Pacific and South-East Asian species of the new orb-weaving spider genus Plebs with Plebs eburnus (Keyserling, 1886) as type species are revised. Following this study, Plebs includes a total of 22 species of which seven are here described new. Seven species are found in Australia, two in the Pacific region (New Caledonia, Vanuatu), and two in South-East Asia (Papua New Guinea, The Philippines). Eleven Asian species are transferred to the new genus. Plebs represent comparatively small orb-weaving spiders of c. 1.2–15.0 mm body length with a slightly elongated abdomen and humeral (shoulder) humps. Males of most species have two to three stout setae on the ventral side of their fourth coxae. Male pedipalps are characterized by the presence of a single macroseta on the patella, the presence of a paramedian apophysis as basal extension of the conductor, and an apical tegular protrusion. The female epigyne has a scape that is generally much longer than wide. It does not have a terminal pocket and is frequently broken off in a number of species. A phylogenetic analysis of 15 species of Plebs (those for which both sexes are known), 13 Australian/Pacific orb-weaving spider species representing the most commonly collected clades with paramedian apophysis, three species of Nearctic Eriophora Simon, 1864, and Araneus diadematus Clerck, 1758, as outgroup, identified a single synapomorphy of Plebs based on 35 morphological and three behavioural characters: a distinct, inverted U-shaped light pattern on the ventral side of the abdomen with two additional white spots anterolateral to the spinnerets. This analysis recovered a monophyletic clade of all Asian Plebs, suggesting a single colonization event of the genus that putatively originated in Australia. Most Plebs species appear to be active during the day. They build a regular orb-web with vertical stabilimentum in grass and low shrubs. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166, 279–341.

An organic coating keeps orb-weaving spiders (Araneae, Araneoidea, Araneidae) from sticking to their own capture threads

More than 95% of orb-weaving spider species ensure prey capture success by producing viscous threads equipped with gluey droplets. However, this trap may bear serious risks for the web-inhabiting spider as well. The obvious question, how a spider avoids getting stuck in its own capture spiral, has gained little scientific attention up till now. In 1905, the French naturalist Jean-Henry Fabre concluded from anecdotal observation that orb-weaving spiders protect themselves by a fatty surface coating. Here, we test this hypothesis by indirectly measuring the force necessary to detach an autotomized spider’s leg from the capture spiral of its own web (here called ‘index of adhesion’, IOA). Three groups of legs, each of the species Araneus diadematus Clerck, 1757 and Larinioides sclopetarius (Clerck, 1757), were tested. One was left untreated, one was washed with distilled water (H2O), and one was washed with the organic solvent carbon disulphide (CS2). In both species, we found a weak IOA between the spider leg and the gluey capture spiral in untreated and water-washed legs without significant differences between the two. The IOA approximately doubled, when spider legs had been washed with carbon disulphide prior to measurement, that is, the CS2-washed legs stuck significantly more strongly than the untreated and water-washed legs. These results provide indirect evidence for a protective anti-adhesive organic coating on the spider’s body surface and so support Fabre’s hypothesis. Über 95% der Radnetz-bauenden Spinnen benutzen einen klebrigen Faden mit komplex aufgebauten Klebstoff-Tröpfchen zum Beutefang. Ein derartiger Fangfaden birgt aber auch für die Spinne Risiken. Die naheliegende Frage, wie es eine Spinne vermeidet, im eigenen Fangfaden kleben zu bleiben, wurde bisher kaum untersucht. Im Jahr 1905 schloss der französische Naturforscher Jean-Henry Fabre aus einzelnen Beobachtungen, dass sich Radnetzspinnen mittels eines fettigen Schutzfilms auf ihrem Körper vor dem Klebstoff schützen. Diese Hypothese wurde bisher nie überprüft. Wir maßen auf indirektem Wege die Kraft, die nötig ist, um ein autotomiertes Spinnenbein aus der Fangspirale des eigenen Netzes zu lösen. Je drei Gruppen von Beinen der Arten Araneus diadematus Clerck, 1757 und Larinioides sclopetarius (Clerck, 1757) wurden getestet. Eine Gruppe blieb unbehandelt, die zweite wurde mit destilliertem Wasser (H2O) gewaschen, die dritte mit dem organischen Lösungsmittel Schwefelkohlenstoff (CS2). Beine beider Arten hafteten schwach am Klebfaden, wenn sie unbehandelt geblieben oder mit Wasser gewaschen waren, ohne dass es einen signifikanten Unterschied zwischen den beiden Gruppen gab. Mit Schwefelkohlenstoff behandelte Beine hafteten etwa doppelt so stark wie die unbehandelten oder mit Wasser gewaschenen Beine am Fangfaden. Unsere Resultate liefern einen indirekten Beleg für einen organischen anti-adhäsiven Oberflächenschutzfilm bei araneoiden Spinnen und unterstützen daher Fabres Hypothese.

Niche partitioning in orbweaving spiders Meta menardi and Metellina merianae (Tetragnathidae)

Hypogean habitats are relatively simple exhibiting low diversity, low production and relative constancy of environmental factors, and are therefore appropriate for studying species coexistence in situ. We investigated the coexistence of two closely related, similarly sized orb-weaving spider species, Meta menardi and Metellina merianae, living syntopically in a Slovenian cave. We studied the annual dynamics of both species within a mixed population, and the impact of the ambient temperature, relative humidity, airflow and illumination, and compared their trophic niches to legacy data on prey of both species from 55 caves in Slovenia. We predicted a large overlap in their spatial niches and substantial differences in their temporal and trophic niches. We found that their spatial niches overlap greatly with few exceptions, mostly on the dates of notable meteorological changes in the cave but that their temporal niches differ significantly with r-strategy resembling epigean annual dynamic in M. merianae and a steady low abundance course in M. menardi within the cave. We also found that different predatory strategies significantly segregate their trophic niches: M. merianae uses a typical orb-weaving hunting strategy, while M. menardi combines web hunting with off-web hunting. Our findings suggest that both the diverse dynamics and trophic niches enable the coexistence of M. menardi and M. merianae despite their similar spatial niches, and that M. menardi, in particular, is optimally adapted to the epigean/hypogean ecotone.

Behavioural and biomaterial coevolution in spider orb webs

Mechanical performance of biological structures, such as tendons, byssal threads, muscles, and spider webs, is determined by a complex interplay between material quality (intrinsic material properties, larger scale morphology) and proximate behaviour. Spider orb webs are a system in which fibrous biomaterials--silks--are arranged in a complex design resulting from stereotypical behavioural patterns, to produce effective energy absorbing traps for flying prey. Orb webs show an impressive range of designs, some effective at capturing tiny insects such as midges, others that can occasionally stop even small birds. Here, we test whether material quality and behaviour (web design) co-evolve to fine-tune web function. We quantify the intrinsic material properties of the sticky capture silk and radial support threads, as well as their architectural arrangement in webs, across diverse species of orb-weaving spiders to estimate the maximum potential performance of orb webs as energy absorbing traps. We find a dominant pattern of material and behavioural coevolution where evolutionary shifts to larger body sizes, a common result of fecundity selection in spiders, is repeatedly accompanied by improved web performance because of changes in both silk material and web spinning behaviours. Large spiders produce silk with improved material properties, and also use more silk, to make webs with superior stopping potential. After controlling for spider size, spiders spinning higher quality silk used it more sparsely in webs. This implies that improvements in silk quality enable 'sparser' architectural designs, or alternatively that spiders spinning lower quality silk compensate architecturally for the inferior material quality of their silk. In summary, spider silk material properties are fine-tuned to the architectures of webs across millions of years of diversification, a coevolutionary pattern not yet clearly demonstrated for other important biomaterials such as tendon, mollusc byssal threads, and keratin.

Discovery of the largest orbweaving spider species: the evolution of gigantism in Nephila.

BackgroundMore than 41,000 spider species are known with about 400–500 added each year, but for some well-known groups, such as the giant golden orbweavers, Nephila, the last valid described species dates from the 19th century. Nephila are renowned for being the largest web-spinning spiders, making the largest orb webs, and are model organisms for the study of extreme sexual size dimorphism (SSD) and sexual biology. Here, we report on the discovery of a new, giant Nephila species from Africa and Madagascar, and review size evolution and SSD in Nephilidae.MethodologyWe formally describe N. komaci sp. nov., the largest web spinning species known, and place the species in phylogenetic context to reconstruct the evolution of mean size (via squared change parsimony). We then test female and male mean size correlation using phylogenetically independent contrasts, and simulate nephilid body size evolution using Monte Carlo statistics.Conclusions Nephila females increased in size almost monotonically to establish a mostly African clade of true giants. In contrast, Nephila male size is effectively decoupled and hovers around values roughly one fifth of female size. Although N. komaci females are the largest Nephila yet discovered, the males are also large and thus their SSD is not exceptional.

Partitioning of Niches Among Four Species of Orb-Weaving Spiders in a Grassland Habitat

Partitioning of niches can play an important role in structuring faunal communities. We tested the hypothesis that differences between four species of orb-weaving spiders (Araneidae) in body size and the structure and position of their webs resulted in their partitioning the available prey. The study species are sympatric in a grassland habitat and included Argiope trifasciata (Forskål), Cyclosa turbinata (Walckenaer), Mangora gibberosa (Hentz), and Neoscona arabesca (Walckenaer). The spider species differed in body size, web diameter, height of web above the ground, spacing of mesh within webs, and the type of plant to which the web was attached. The spider species had a generalist diet and captured prey of multiple trophic levels. Nevertheless, the hypothesis was supported: the spider species differed in the types of prey that they captured. Partitioning of the available prey was influenced by body size, with larger spiders capturing larger prey, but not by the structure or position of their webs. Differences between spider species in niche may reduce competitive interactions and allow them to coexist in sympatry.

Not from “Down Under”: new synonymies and combinations for orb-weaving spiders (Araneae: Araneidae) erroneously reported from Australia

The examination of type material of presumed Australian orb-weaving spiders as part of a revision of the Araneidae of this country revealed that a number of species are not from Australia. The Natural History Museum, Vienna (Austria) holds the type material of three species of orb-weaving spiders that were originally described from Australia, however all of the species are undoubtedly of American, most likely southern Brazilian, origin and it is unlikely that they were collected in Australia. We propose the following synonymies and generic transfers: Acacesia tenella (L. Koch, 1871) comb. nov. (= Acacesia cornigera Petrunkevitch, 1925 new synonymy); Alpaida navicula (L. Koch, 1871) comb. nov. (= Alpaida roemeri (Strand, 1908) new synonymy); and Eustala mucronatella (Roewer, 1942) comb. nov. In addition, Novearanea queribunda (Keyserling, 1887) comb. nov. (= Araneus quaesitus (Keyserling, 1887) new synonymy; = Novaranea laevigata (Urquhart, 1891) new synonymy) is a New Zealand orb-weaving spider based on the labels that were found with the type specimens housed at the Natural History Museum, London (England). In the original description no locality data was given for N. queribunda and “Australien” was erroneously listed for A. quaesitus.

The contribution of axial fiber extensibility to the adhesion of viscous capture threads spun by orb-weaving spiders

The viscous capture threads produced by over 4000 species of orb-weaving spiders are formed of regularly spaced aqueous droplets supported by a pair of axial fibers. These threads register increased stickiness when spans of increasing lengths contact a surface, indicating that adhesion is recruited from multiple droplets. This study examined threads produced by five species to test the hypothesis that axial fiber extensibility is crucial for this summation of adhesion. It did so by comparing the stickiness of unstretched threads with threads that had been elongated to reduce the extensibility of their axial fibers. As stretching these threads also increased the distance between their droplets, we measured the stickiness of stretched threads with contact plates whose widths were increased in proportion to the degree of thread elongation. We then accounted for the actual thread elongation achieved for each individual's threads and for differences in the five species' absolute thread extensibility. The results showed that in four species thread extensibility contributed positively to adhesion. For three species, thread extensibility and droplet volume together explained the mean per droplet adhesion of threads. Models based on these three species show that, as threads were elongated, increasing amounts of potential adhesion were lost to diminished axial fiber extensibility. These models indicate that approximately one-third of an unstretched viscous thread's stickiness accrues from the adhesive recruitment made possible by axial fiber extensibility.

Spider capture silk: performance implications of variation in an exceptional biomaterial

Spiders and their silk are an excellent system for connecting the properties of biological materials to organismal ecology. Orb-weaving spiders spin sticky capture threads that are moderately strong but exceptionally extensible, resulting in fibers that can absorb remarkable amounts of energy. These tough fibers are thought to be adapted for arresting flying insects. Using tensile testing, we ask whether patterns can be discerned in the evolution of silk material properties and the ecological uses of spider capture fibers. Here, we present a large comparative data set that allows examination of capture silk properties across orb-weaving spider species. We find that material properties vary greatly across species. Notably, extensibility, strength, and toughness all vary approximately sixfold across species. These material differences, along with variation in fiber size, dictate that the mechanical performance of capture threads, the energy and force required to break fibers, varies by more than an order of magnitude across species. Furthermore, some material and mechanical properties are evolutionarily correlated. For example, species that spin small diameter fibers tend to have tougher silk, suggesting compensation to maintain breaking energy. There is also a negative correlation between strength and extensibility across species, indicating a potential evolutionary trade-off. The different properties of these capture silks should lead to differences in the performance of orb webs during prey capture and help to define feeding niches in spiders.

HAVE MALE AND FEMALE GENITALIA COEVOLVED? A PHYLOGENETIC ANALYSIS OF GENITALIC MORPHOLOGY AND SEXUAL SIZE DIMORPHISM IN WEB-BUILDING SPIDERS (ARANEAE: ARANEOIDEA)

Sexual size dimorphism (SSD) can strongly influence the evolution of reproductive strategies and life history. If SSD is extreme, and other characters (e.g., genitalic size) also increase with size, then functional conflicts may arise between the sexes. Spiders offer an excellent opportunity to investigate this issue because of their wide range of SSD. By using modern phylogenetic methods with 16 species of orb-weaving spiders, we provide strong evidence for the "positive genitalic divergence" model, implying that sexual genitalic dimorphism (SGD) increases as SSD increases. This pattern is supported by an evolutionary mismatch between the absolute sizes of male and female genitalia across species. Indeed, our findings reveal a dramatic reversal from male genitalia that are up to 87x larger than female genitalia in size-monomorphic species to female genitalia that are up to 2.8x larger in extremely size-dimorphic species. We infer that divergence in SGD could limit SSD both in spiders, and potentially in other taxa as well. Further, male and female body size, as well as male and female genitalia size, are decoupled evolutionarily. Finally, we show a negative scaling (hypoallometry) of male and female genitalic morphology within sexes. Evolutionary forces specific to each sex, such as larger female size (increased fecundity) or smaller male size (enhanced mate-searching ability), may be balanced by stabilizing selection on relative genitalic size.

HAVE MALE AND FEMALE GENITALIA COEVOLVED? A PHYLOGENETIC ANALYSIS OF GENITALIC MORPHOLOGY AND SEXUAL SIZE DIMORPHISM IN WEB-BUILDING SPIDERS (ARANEAE: ARANEOIDEA)

Sexual size dimorphism (SSD) can strongly influence the evolution of reproductive strategies and life history. If SSD is extreme, and other characters (e.g., genitalic size) also increase with size, then functional conflicts may arise between the sexes. Spiders offer an excellent opportunity to investigate this issue because of their wide range of SSD. By using modern phylogenetic methods with 16 species of orb-weaving spiders, we provide strong evidence for the "positive genitalic divergence" model, implying that sexual genitalic dimorphism (SGD) increases as SSD increases. This pattern is supported by an evolutionary mismatch between the absolute sizes of male and female genitalia across species. Indeed, our findings reveal a dramatic reversal from male genitalia that are up to 87x larger than female genitalia in size-monomorphic species to female genitalia that are up to 2.8x larger in extremely size-dimorphic species. We infer that divergence in SGD could limit SSD both in spiders, and potentially in other taxa as well. Further, male and female body size, as well as male and female genitalia size, are decoupled evolutionarily. Finally, we show a negative scaling (hypoallometry) of male and female genitalic morphology within sexes. Evolutionary forces specific to each sex, such as larger female size (increased fecundity) or smaller male size (enhanced mate-searching ability), may be balanced by stabilizing selection on relative genitalic size.

Safer sex with feeding females: sexual conflict in a cannibalistic spider

Mating strategies are to a large degree shaped by conflicts between the sexes, causing a rapid antagonistic coevolution of traits involved in reproduction. The view that sexual cannibalism represents a form of sexual conflict leads to the prediction of male traits that facilitate escape from cannibalistic females. A variety of traits have been suggested to serve this function in spiders, where sexual cannibalism is comparatively common. Empirical evidence, however, is virtually absent. Here we show experimentally that opportunistic mating with feeding females, which has been reported from several species of orb-weaving spiders, greatly reduces the risk of cannibalism and injury for males in the spider Nephila fenestrata. This has direct consequences for a male's fertilization success because surviving males can reduce the female's remating probability by guarding her against rivals. Although copulation with previously mated females sometimes appears to be mechanically impossible, second males that do copulate can expect to fertilize on average 64% of a female's eggs. Our results support the view that opportunistic mating may have evolved as a male tactic in a context of sexual conflict over sexual cannibalism.

COMPARATIVE NESTING BEHAVIOR OF EPISYRON QUINQUENOTATUS (HYMENOPTERA: POMPILIDAE) IN THE NORTHEASTERN UNITED STATES

The nesting behavior of >150 females of Episyron quinquenotatus was studied comparatively at eight localities in the northeastern United States from 1967 to 1993. The two major study sites, Presque Isle State Park, Erie County, PA, and Auburn, Cayuga County, NY, were investigated mainly during 1967–1969. Wasps nesting in sand at Presque Isle dug longer and deeper burrows more rapidly than females nesting in loamy fine sand at Auburn. Females at Auburn were smaller than those at Presque Isle and transported prey spiders mainly on the ground. The prey spiders at Presque Isle were often carried in flight by the larger wasps. Mechanics of nest closure sometimes differed between wasps at the two localities. Females captured six genera and nine species of orb-weaving spiders (Araneidae) at seven localities. Araneus patagiatus adult females, A. diadematus immatures, and Eustala anastera adult females were predominant prey at Presque Isle while Araniella displicata adult females and Neoscona arabesca adult females were prevalent prey at Auburn. Larger wasps laid larger eggs. There was a positive correlation between size of prey spider and size of wasp produced in the next generation. Females at Presque Isle sometimes completed two or, rarely, three nests per day.

Stabilimenta characteristics of the spider Argiope argentata on small islands: support of the predator-defense hypothesis

A variety of orb-weaving spider species construct stabilimenta, patterned areas of dense silk, typically near the hub of the orb. The adaptive significance of this construction, along with associated behaviors such as shuttling and vibrating, is much debated. Arigiope argentata on small islands of the Bahamas frequently possess stabilimenta; we studied 397 individuals of this species to investigate possible functions of their stabilimenta, paying particular attention to predator-defense hypotheses. Cruciform stabilimenta were commoner in all size classes of spiders than discoid stabilimenta or no stabilimentum at all; discoid stabilimenta occurred mostly among intermediate size classes. Within the cruciform type, two-segmented stabilimenta were especially common among the very smallest spiders. Size of cruciform stabilimenta showed a curvilinear relation to spider body length; the fitted curve for “total segment length” had a maximum at an intermediate spider length. We argue that this relationship (among other phenomena) supports an apparently-larger-size hypothesis, whereby intermediate-sized spiders in particular appear much larger than they actually are. This could discourage predators, including those that are gape-limited such as lizards. We argue that stabilimenta in the smallest spiders, in which typically two segments are opposed, so that they more or less “line up”, serve as camouflage. When disturbed experimentally, spiders with discoid stabilimenta shuttle to the opposite side of the centrally located stabilimentum. This seems an obvious defensive behavior and occurs less frequently among spiders with cruciform stabilimenta. Large spiders vibrate more frequently than small ones, but no relation exists between vibration frequency and stabilimentum type. We argue (see also Tolbert 1975) that vibrating behavior, in which the spider can become a blur, renders its location more difficult to discern and the spider more difficult to grasp, rather than increasing apparent size.