Anti-predator defences of Pholcus phalangioides (Araneae, Pholcidae), a web-building and web-invading spider

The behaviours used by Pholcus phalangioides (Fuesslin) (Araneae, Pholcidae) to evade its predators were studied with particular attention being given to a special defence behaviour, whirling. To whirl, this long-legged web-building spider swings its body around in a circle, with its legs remaining on the silk. Experiments were carried out to determine the types of stimuli that elicited whirling. Touching the spider or its web elicited whirling, as did air movement over the spider, but there was no evidence that chemical stimuli from potential predators were important. Small juveniles differed from adult females and larger juveniles by more often dropping from the web instead of whirling when confronted by a potential predator. Besides catching prey on its own web P. phalangioides invades other spiders' webs to catch the other spiders. By whirling in alien webs, P. phalangioides could deter attacks by the resident spider, but P. phalangioides was less inclined to whirl when in an alien than when in its own web.     

The Trochidae and Turbinidae of the Kermadec Ridge (Mollusca: Gastropoda)

Abstract

Taieria erebus (Gnaphosidae) was found to be a versatile predator: it captured insects both cursorially (away from webs) and kleptopar-asitically (on alien webs); it captured spiders in both the presence and absence of webs; and it also ate the eggs of host spiders (oophagy). When T. erebus invaded webs, it was as an aggressive mimic — it performed a repertoire of vibratory behaviours to lure the host spider. Although T. erebus pursued and captured spiders on diverse web-types, it was more effective as a predator when invading densely (rather than sparsely) woven cribellate and non-sticky webs, and was especially effective on non-cribellate sticky webs. Gnaphosids are traditionally referred to as hunting spiders, but T. erebus built a small prey-capture web. T. erebus also preyed on segestriid spiders, then used their webs to catch more prey, this being an unusual example of a spider using, as a tool for predation, the spinning-work of another species from an unrelated family. T. erebus used specialised behaviours to prey on nesting cursorial spiders. Prey was either grasped or stabbed; the venom of T. erebus was highly potent against spiders. Experiments indicated that vision was of little or no importance in the predatory behaviour of T. erebus. The behaviour of T. erebus is compared to that of Portia, a web-building salticid spider which is very versatile in its predatory behaviour and has acute vision. T. erebus is discussed in relation to hypotheses concerning gnaphosid and salticid evolution.     

Predator-prey interactions between jumping spiders (Araneae, Salticidae) and Phokus phalangioides (Araneae, Pholcidae)

Portia is a genus of specialized web-invading salticids that use aggressive mimicry. Some other salticids leap into webs to catch spiders but do not use aggressive mimicry. Pholcus phalangioides is a web-building spider with a special defensive behaviour—called whirling—in which it swings its body around in a circle while keeping its long legs on the silk. Pholcus phalangioides is preyed on by Portia and probably other salticid spiders in nature. Interactions between P. phalangioides and 13 species of salticids were studied in the laboratory to compare how effective salticids with different styles of predation were at catching the pholcids. Four species of Portia were studied and each was more efficient at catching P. phalangioides than were the other nine salticids tested. For one species—Portia fimbriata—individuals from three different populations were studied. The Queensland P. fimbriata used aggressive mimicry more consistently and were more efficient at catching P. phalangioides than were the other species of Portia and the other populations of P. fimbriata . The salticids that were the most efficient at catching pholcids were also better able to avoid setting off whirling by the pholcids. An experiment in which pholcids were artificially induced to whirl whenever the predator was near provided additional evidence that whirling is an effective defence of pholcids against predation by salticids.     

Comparative biology of Portia africana,P. albimana,P. fimbriata,P. labiata,and P. shultzi,araneophagic, web-building jumping spiders (Araneae: Salticidae): Utilisation of webs,predatory versatility,and intraspecific interactions

Abstract

Portia is a behaviourally complex and aberrant salticid genus. The genus is of unusual importance because it is morphologically primitive. Five species were studied in nature (Australia, Kenya, Malaysia, Sri Lanka) and in the laboratory in an effort to clarify the origins of the salticids and of their unique, complex eyes. All the species of Portia studied were both web builders and cursorial. Portia was also an araneophagic web invader, and it was a highly effective predator on diverse types of alien webs. Portia was an aggressive mimic, using a complex repertoire of vibratory behaviour to deceive the host spiders on which it fed. The venom of Portia was unusually potent to other spiders; its easily autotomised legs may have helped Portia escape if attacked by its frequently dangerous prey. Portia was also kleptoparasitic and oophagic when occupying alien webs. P. fimbriata from Queensland, where cursorial salticids were superabundant, used a unique manner of stalking and capturing other salticids. The display repertoires used during intraspecific interactions were complex and varied between species. Both visual (typical of other salticids) and vibratory (typical of other web spiders) displays were used. Portia copulated both on and away from webs and frequently with the female hanging from a dragline. Males cohabited with subadult females on webs, mating after the female matured. Adult and subadult females sometimes used specialised predatory attacks against courting or mating males. Sperm induction in Portia was similar to that in other cursorial spiders. Portia mimicked detritus in shape and colour, and its slow, mechanical locomotion preserved concealment. Portia occasionally used a special defensive behaviour (wild leaping) if disturbed by a potential predator. Two types of webs were spun by all species (Type 1, small resting platforms; Type 2, large prey-capture webs). Two types of egg sacs were made, both of which were highly aberrant for a salticid. Responses of different species and both sexes of Portia were quantitatively compared for different types of prey. Many of the trends in behaviour within the genus, including quantitative differences in predatory behaviour, seemed to be related to differences in the effectiveness of the cryptic morphology of Portia in concealing the spider in its natural habitat (‘effective crypsis’). The results of the study supported, in general, Jackson & Blest’s (1982a) hypothesis of salticid evolution which, in part, proposes that salticid ancestors were web builders with poorly developed vision and that acute vision evolved in conjunction with the ancestral spiders becoming proficient as araneophagic invaders of diverse types of webs.     

Predator-prey interactions between web-invading jumping spiders and Argiope appensa (Araneae, Araneidae), a tropical orb-weaving spider

A range of web-invading jumping spiders with different predatory strategies was tested with A. appensa in the laboratory: Mimetus maculosus (Mimetidae), Pholcus phalangioides (Pholcidae), Taieria erebus (Gnaphosidae), and 11 species of salticids. Spiders that are known to specialize at web-invading, either by leaping into webs or by walking slowly into webs and practising aggressive mimicry, captured A. appensa ; three salticid species not known to be web-invaders never did. Web-invaders that practised aggressive mimicry were more efficient than were species that only leapt into webs. Portia fimbriata from Queensland was the most consistent at using aggressive mimicry and was also the most efficient at catching A. appensa . Web-invaders that were more efficient at catching A. appensa were also better able to avoid setting off pumping, a special defence behaviour used by A. appensa . Portia fimbriata from Queensland was especially efficient at avoiding setting off pumping: P. fimbriata more consistently than other Portia made its final approach toward A. appensa by coming down from above the web on a dragline and making minimal contact with the web. An experiment, in which A. appensa was artificially induced to pump whenever the predator was near, provided additional evidence that pumping is effective in defending A. appensa against web-invaders.     

Long-duration whirling of Pholcus phalangioides (Araneae, Pholcidae) is specifically elicited by Salticid spiders

Long-duration whirling (gyrating of the body during several hours a day) was shown by the pholcid spider Pholcus phalangioides to salticid spiders and hardly ever to predatory spiders from eight other families in laboratory arenas. Long-duration whirling has not been reported so far, in contrast to short-duration whirling lasting less than a few minutes. Long-duration whirling may have the anti-predatory function of disturbing continual visual fixation of prey in attacking salticids, in contrast to short-duration whirling that has been demonstrated to favour survival of pholcids in the presence of all sorts of predatory spiders.     

The biology of New Zealand and Queensland pirate spiders (Araneae, Mimetidae): aggressive mimicry, araneophagy and prey specialization

Mimetus sp. indet. and Mimetus maculosus , from New Zealand and Australia, respectively, were studied in the laboratory and in nature. Behaviourally, the two species were very similar. Each was found to be primarily an araneophagic spider which invaded alien webs, acted as an aggressive mimic by performing a variety of vibratory behaviours to which the prey-spider responded as it normally would to its own prey, and attacked by lunging at close range, subduing its victim with a strong, apparently spider-specific venom while holding the spider in a 'basket' formed by its spine-covered legs. In nature, these mimetids were observed to feed on a restricted range of spiders: orb web-building araneids and space web-building theridiids. Sometimes, they occupied other types of webs, but in the laboratory they captured only araneids and theridiids efficiently. They captured non-cribellate amaurobiids considerably less efficiently, and never captured other types of spiders. Occasionally, the mimetids fed on insects ensnared in araneid and theridiid webs and on eggs of theridiids. Experimental evidence indicated that vision was of little or no importance in the predatory behaviour of these mimetids. The behaviour of the mimetids is compared to that of Portia , an araneophagic web-invading salticid, and the results of this study are discussed in relation to hypotheses concerning salticid evolution.     

Variable dependence on detrital and grazing food webs by generalist predators: aerial insects and web spiders

Recent studies have shown that organisms from the detritus food web subsidize generalist predators in aboveground food webs, but its significance in space and time is largely unknown. Here we report seasonal dynamics of aerial insects from grazing and detritus food webs in both forest and grassland habitats, and show how these patterns influence the dependence of web spiders on the detritus food web. Detrital insects were more abundant in spring, decreased in summer, and then increased slightly in autumn. This pattern was most conspicuous in Nematocera. Due to different seasonal activity patterns of grazing and detrital insects, the proportion of detrital insects was greater in spring and autumn. Detrital insects were relatively more abundant in the forest than in the grassland. Prey captured by web spiders generally reflected seasonal and spatial patterns of aerial insect abundance. In particular, Leucauge spiders reversed their dependence on the two food webs seasonally. Body size of spiders was negatively correlated with the proportion of detrital prey, suggesting that the detrital subsidy is essential for relatively small predators. This size effect probably resulted from interaction of the following two factors: 1) the maximum body size of prey that can be caught increased with spider body size, 2) larger body size classes of aerial insects included a higher proportion of insects from the grazing food web.     

Spiders Use Airborne Cues to Respond to Flying Insect Predators by Building Orb-Web with Fewer Silk Thread and Larger Silk Decorations

Orb-web spiders are an important group of trap-building animals that feed upon an array of insect prey and are themselves the prey of wasps and parasitoid flies. The purpose of this study was to examine whether spiders use airborne vibration cues to respond to these flying insect predators by changing their web-building behavior. While on its web waiting for prey, the orb-web spider Eriophora sagana was exposed to a vibrating tuning fork that emitted an airborne vibration signal. The signal mimicked the approach of flying insect predators and its effect on the subsequent web building was examined. No stimulus was provided during web building. A significant treatment effect was observed with respect to the total thread length (TTL) and area of the silk decoration (conspicuous white structure attached to the orb-webs of diurnal spiders) of their webs. While control spiders increased the TTL in their second web, the stimulus group spiders did not, providing the first evidence that orb-web spiders use airborne vibration cues to assess the predation risk and change their foraging activity. It also indicates that spiders remember an encounter with a predator on their webs and use this information later to adjust their web building. My findings imply that spiders devote less effort to foraging (i.e. web building) in response to the presence of their predators, which is considered to reduce their foraging efficiency. In contrast, the stimulus group spiders increased the area of their silk decoration significantly more in their second webs than did the control spiders. This is considered an experimental support for the hypothesis that silk decorations have an anti-predator function.     

Functionally independent components of prey capture are architecturally constrained in spider orb webs

Evolutionary conflict in trait performance under different ecological contexts is common, but may also arise from functional coupling between traits operating within the same context. Orb webs first intercept and then retain insects long enough to be attacked by spiders. Improving either function increases prey capture and they are largely determined by different aspects of web architecture. We manipulated the mesh width of orbs to investigate its effect, along with web size, on prey capture by spiders and found that they functioned independently. Probability of prey capture increased with web size but was not affected by mesh width. Conversely, spiders on narrow-meshed webs were almost three times more likely to capture energetically profitable large insects, which demand greater prey retention. Yet, the two functions are still constrained during web spinning because increasing mesh width maximizes web size and hence interception, while retention is improved by decreasing mesh width because more silk adheres to insects. The architectural coupling between prey interception and retention has probably played a key role in both the macroevolution of orb web shape and the expression of plasticity in the spinning behaviours of spiders.     

Caught in the web: Spider web architecture affects prey specialization and spider–prey stoichiometric relationships

Quantitative approaches to predator–prey interactions are central to understanding the structure of food webs and their dynamics. Different predatory strategies may influence the occurrence and strength of trophic interactions likely affecting the rates and magnitudes of energy and nutrient transfer between trophic levels and stoichiometry of predator–prey interactions. Here, we used spider–prey interactions as a model system to investigate whether different spider web architectures—orb, tangle, and sheet‐tangle—affect the composition and diet breadth of spiders and whether these, in turn, influence stoichiometric relationships between spiders and their prey. Our results showed that web architecture partially affects the richness and composition of the prey captured by spiders. Tangle‐web spiders were specialists, capturing a restricted subset of the prey community (primarily Diptera), whereas orb and sheet‐tangle web spiders were generalists, capturing a broader range of prey types. We also observed elemental imbalances between spiders and their prey. In general, spiders had higher requirements for both nitrogen (N) and phosphorus (P) than those provided by their prey even after accounting for prey biomass. Larger P imbalances for tangle‐web spiders than for orb and sheet‐tangle web spiders suggest that trophic specialization may impose strong elemental constraints for these predators unless they display behavioral or physiological mechanisms to cope with nutrient limitation. Our findings suggest that integrating quantitative analysis of species interactions with elemental stoichiometry can help to better understand the occurrence of stoichiometric imbalances in predator–prey interactions.     

The comparative study of the predatory behaviour of Myrmarachne, ant-like jumping spiders (Araneae: Salticidae)

The predatory behaviour of 31 species of Myrmarachne , ant-like salticids, was studied in the laboratory and the field. The ant-like morphology and locomotion of these spiders appears to function primarily in Batesian mimicry. No evidence was found of Myrmarachne feeding on ants. However, predatory sequences were found to differ considerably from those typical of salticids. Instead of stalking and leaping on prey, Myrmarachne lunged at prey from close range. Myrmarachne used its legs I to tap prey before lunging, another unusual behaviour for a salticid. Myrmarachne fed on a wide range of arthropod prey in nature and the laboratory, but appears to be especially efficient at catching moths. Also, Myrmarachne tends to open up, or enter into, other spiders' nests and eat other spiders' eggs. Myrmarachne males were less efficient than females, in laboratory tests, at catching various types of arthropod prey, but they appear to be as efficient as females at oophagy. Myrmarachne tend to use webs of other spiders as nest sites, but no evidence was found of Myrmarachne preying on spiders in webs. It appears that the unusual features of Myrmarachne's predatory and nesting behaviour are important in enabling these spiders to preserve their ant-like appearance.     

Does the Giant Wood Spider Nephila pilipes Respond to Prey Variation by Altering Web or Silk Properties?

Recent studies demonstrated that orb‐weaving spiders may alter web architectures, the amount of silk in webs, or the protein composition of silks in response to variation in amount or type of prey. In this study, we conducted food manipulations to examine three mechanisms by which orb‐weaving spiders may adjust the performance of webs to variation in prey by altering the architectures of webs, making structural changes to the diameters of silk threads, and manipulating the material properties or amino acid composition of silk fibers. We fed Nephila pilipes two different types of prey, crickets or flies, and then compared orb structure and the chemical and physical properties of major ampullate (MA) silk between groups. Prey type did not affect orb structures in N. pilipes, except for mesh size. However, MA silk diameter and the stiffness of orbs constructed by spiders fed crickets were significantly greater than for the fly group. MA fibers forcibly silked from N. pilipes fed crickets was significantly thicker, but less stiff, than silk from spiders fed flies. Spiders in the cricket treatment also produced MA silk with slightly, but statistically significantly, more serine than silk from spiders in the fly treatment. Percentages of other major amino acids (proline, glycine, and glutamine) did not differ between treatments. This study demonstrated that orb‐weaving spiders can simultaneously alter some structural and material properties of MA silk, as well as the physical characteristics of webs, in response to different types of prey.     

Kleptoparasites influence foraging behaviour of the spider <Emphasis Type="Italic">Stegodyphus lineatus</Emphasis> (Araneae,Eresidae)

Prey captured by a predator may attract kleptoparasites which could significantly reduce the amount of food consumed. Stegodyphus lineatus, a cribellate spider, builds an energetically costly web. Ants raid the webs of S. lineatus to steal prey and behave as kleptoparasites. We investigated ant raids in a natural population of S. lineatus and their influence on the spider’s foraging behaviour. Considering spiders that had captured a prey, 31.2% suffered an ant raid within 24 h after the prey capture. Experimental tests showed that the response to ant raid is to delay web rebuilding and this was independent of a spider’s previous foraging success. There was a tendency for spiders that were exposed to ants to build larger webs. Neither prey-handling duration nor prey consumption was modified after exposure to ants. These results suggest that Stegodyphus lineatus adapt its web-building behaviour in response to the risk of kleptoparasitism.     

Prey preferences ofPortia fimbriata,an araneophagic,web-building jumping spider (Araneae: Salticidae) from Queensland

Portia fimbriata from Queensland, a previously studied jumping spider (Salticidae), routinely includes web-building spiders and cursorial salticids in its diet, both of these types of prey being dangerous and unusual prey for a salticid. The present paper is the first detailed study ofP. fimbriata's prey preferences. Three basic types of tests of prey preference were used, providing evidence that (1)P. fimbriata males and females prefer spiders (both web-building spiders in webs and salticids away from webs) to insects; (2)P. fimbriata males and females prefer salticids to web-building spiders; (3)P. fimbriata males and females prefer larger spiders to smaller spiders; (4) there are intersexual differences in the preferences ofP. fimbriata for prey size, females preferring larger prey and males preferring smaller prey; and (5)P. fimbriata's prey preferences are not affected by a prior period without food of 2 weeks. When preferences were tested for by using both living, active prey and dead, motionless lures, the same preferences were expressed, indicating thatP. fimbriata can distinguish among different types of prey independent of the different movement patterns of different prey.     

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.     

The multiple disguises of spiders: web colour and decorations, body colour and movement

Diverse functions have been assigned to the visual appearance of webs, spiders and web decorations, including prey attraction, predator deterrence and camouflage. Here, we review the pertinent literature, focusing on potential camouflage and mimicry. Webs are often difficult to detect in a heterogeneous visual environment. Static and dynamic web distortions are used to escape visual detection by prey, although particular silk may also attract prey. Recent work using physiological models of vision taking into account visual environments rarely supports the hypothesis of spider camouflage by decorations, but most often the prey attraction and predator confusion hypotheses. Similarly, visual modelling shows that spider coloration is effective in attracting prey but not in conveying camouflage. Camouflage through colour change might be used by particular crab spiders to hide from predator or prey on flowers of different coloration. However, results obtained on a non-cryptic crab spider suggest that an alternative function of pigmentation may be to avoid UV photodamage through the transparent cuticle. Numerous species are clearly efficient locomotory mimics of ants, particularly in the eyes of their predators. We close our paper by highlighting gaps in our knowledge.     

Age-related sequential web building in the colonial spider Metepeira incrassata (Araneidae): an adaptive spacing strategy

Colonial orb-weaving spiders provide insight into the proximate mechanisms by which social animals space themselves within a group. We examined mechanisms for the temporal patterns of web building that determine individual positions in Metepeira incrassata (Araneidae) colonies. The spiders display a characteristic age-related sequence of daily web building, with larger spiders completing their webs significantly earlier than smaller ones. We used data on behavioural interactions, web building, prey capture and predator attacks to evaluate four hypotheses. (1) Larger spiders are better competitors and pre-empt optimal spatial positions. (2) Smaller spiders reduce competition with larger individuals by building webs later. (3) Prey captured by different size classes is available at different times. (4) Differential predation risk determines web-building times. Large individuals dominated behavioural interactions. Disturbances by larger spiders during web construction significantly delayed the completion of smaller individuals' webs and precipitated movements to new web sites. One prediction of the first hypothesis, that spatial needs translate into earlier building, was confirmed by significantly earlier web building by mature females with egg sacs (which are unable to move their egg sacs) compared with same-sized females without eggs (which can change locations freely). Experiments to determine whether the presence of large spiders inhibited the web building of smaller individuals were equivocal. Prey availability and risk of predation are not factors affecting web-building patterns. Sequential web building appears to be a result of both larger spiders competing to pre-empt space from one another and smaller individuals attempting to reduce conflict during web construction. Sequential web building is a proximate mechanism that influences spacing among colonial orb-weaving spiders and helps shape the typical hierarchical size distribution of spiders within the colony. Similar spacing mechanisms may be seen in colonial birds and marine invertebrates. Copyright 2000 The Association for the Study of Animal Behaviour.     

Biomechanical variation of silk links spinning plasticity to spider web function

Spider silk is renowned for its high tensile strength, extensibility and toughness. However, the variability of these material properties has largely been ignored, especially at the intra-specific level. Yet, this variation could help us understand the function of spider webs. It may also point to the mechanisms used by spiders to control their silk production, which could be exploited to expand the potential range of applications for silk. In this study, we focus on variation of silk properties within different regions of cobwebs spun by the common house spider, Achaearanea tepidariorum. The cobweb is composed of supporting threads that function to maintain the web shape and hold spiders and prey, and of sticky gumfooted threads that adhere to insects during prey capture. Overall, structural properties, especially thread diameter, are more variable than intrinsic material properties, which may reflect past directional selection on certain silk performance. Supporting threads are thicker and able to bear higher loads, both before deforming permanently and before breaking, compared with sticky gumfooted threads. This may facilitate the function of supporting threads through sustained periods of time. In contrast, sticky gumfooted threads are more elastic, which may reduce the forces that prey apply to webs and allow them to contact multiple sticky capture threads. Therefore, our study suggests that spiders actively modify silk material properties during spinning in ways that enhance web function.     

Damping capacity is evolutionarily conserved in the radial silk of orb-weaving spiders

Orb-weaving spiders depend upon their two-dimensional silk traps to stop insects in mid flight. While the silks used to construct orb webs must be extremely tough to absorb the tremendous kinetic energy of insect prey, webs must also minimize the return of that energy to prey to prevent insects from bouncing out of oscillating webs. We therefore predict that the damping capacity of major ampullate spider silk, which forms the supporting frames and radial threads of orb webs, should be evolutionarily conserved among orb-weaving spiders. We test this prediction by comparing silk from six diverse species of orb spiders. Silk was taken directly from the radii of orb webs and a Nano Bionix test system was used either to sequentially extend the silk to 25% strain in 5% increments while relaxing it fully between each cycle, or to pull virgin silk samples to 15% strain. Damping capacity was then calculated as the percent difference in loading and unloading energies. Damping capacity increased after yield for all species and typically ranged from 40 to 50% within each cycle for sequentially pulled silk and from 50 to 70% for virgin samples. Lower damping at smaller strains may allow orb webs to withstand minor perturbations from wind and small prey while still retaining the ability to capture large insects. The similarity in damping capacity of silk from the radii spun by diverse spiders highlights the importance of energy absorption by silk for orb-weaving spiders.