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.     

Predator-prey interactions between web-invading jumping spiders and two species of tropical web-building pholcid spiders, Psilochorus sphaeroides and Smeringopus pallidus

Psilochorus sphaeroides from Queensland, Australia and Smeringopus pallidus from Sri Lanka are long-legged, web-building pholcid spiders with a special defence behaviour, whirling. The efficiency of whirling as a defence against web-invading jumping spiders (Salticidae) was examined in the laboratory. Three salticid species were used in these tests- Euryattus sp., Portia fimbriata and Portia labiata. Euryattus leapt into webs, but Portia fimbriata and Portia labiata walked slowly into webs and practised aggressive mimicry. Portia fimbriata was more consistent at using aggressive mimicry and more efficient at capturing Psilochorus sphaeroides and Smeringopus pallidus than was Portia labiata . Both species of Portia were more efficient at catching pholcids than was Euryattus. Portia , especially Portia fimbriata , was less inclined than Euryattus to stimulate pholcids to whirl. In an experiment in which pholcids were artificially induced to whirl whenever a salticid was near, salticids never captured pholcids, providing additional evidence that whirling is an effective defence of Psilochorus sphaeroides and Smeringopus pallidus against web-invaders. Results from this study are compared to those from a study of another pholcid that whirls, Pholcus phalangioides .     

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.     

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.     

The biology of Pholcus phalangioides (Araneae, Pholcidae): predatory versatility, araneophagy and aggressive mimicry

Predatory versatility occurs in Pholcus phalangioides (Fuesslin). In addition to building prey-catching space webs, P. phalangioides invades webs of other spiders and feeds on the occupants. It acts as an aggressive mimic by performing specialized vibratory behaviours to which the prey-spider responds as it normally would to its own prey. Prey (spiders and insects) is attacked by wrapping. Prey that trips over lines at the edge of a web of P. phalangioides , but fails to enter the web, is successfully attacked: P. phalangioides leans out of its web to throw silk over the prey, keeping as few as two legs on the silk. However, P. phalangioides does not attack prey that is completely away from webs. Occasionally, P. phalangioides feeds on eggs of other spiders and on ensnared insects it encounters in alien webs. Experimental evidence indicates that vision is of little or no importance in the predatory behaviour of P. phalangioides . Although P. phalangioides invades diverse types of webs, in addition to using its own web, its efficiency as a predator varies with web-type. It is most efficient as a predator of spiders and, especially, insects on its own web, and least efficient as a predator of amaurobiids on their cribellate sheet webs. Sensory, locomotory and other factors which influence differential predatory efficiency are discussed. The behaviour of P. phalangioides 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.     

Cues for web invasion and aggressive mimicry signalling in Portia (Araneae, Salticidae)

Portia is a web-invading araneophagic spider that uses aggressive mimicry to deceive its prey. The present paper is a first step toward clarifying experimentally the cues that govern Portia's decisions of whether to enter a web, whether to make signals once in a web, and whether to persist at signalling once started. The following conclusions are supported: cues from seeing a web elicit web entry, but volatile chemical cues from webs of prey spiders are not important; seeing a spider in a web increases Portia's inclination to enter the web; after web entry, cues from webs of prey spiders are sufficient to elicit signalling behaviour, even in the absence of other cues coming directly from the prey spider; seeing a prey spider or detecting vibrations on the web make Portia more prone to signal, but volatile chemical cues from prey spiders are not important; once Portia is on a web and signalling, seeing a moving spider and detecting vibrations on the web encourage Portia to persist in signalling; on the basis of visual cues alone, Portia can distinguish between quiescent spiders, insects and eggsacs.     

Predator-prey interactions between web-invading jumping spiders and a web-building spider, Holocnemus pluchei (Araneae, Pholcidae)

Three species of web-invading salticid spiders, with different predatory strategies, were tested with Holocnemus pluchei in the laboratory: Portia fimbriata and Portia labiata , which practise aggressive mimicry, and Euyattus sp., which leaps from outside on to spiders in webs but does not practise aggressive mimicry. Portia was shown to be more efficient than Euryattus at catching H. pluchei. Portia fimbriata from Queensland was more consistent at using aggressive mimicry than was Portia labiata and was also more efficient at catching H. pluchei . The web-invaders that were more efficient at catching H. pluchei were also better able to avoid setting off bouncing, a special defence behaviour used by H. pluchei . An experiment, in which H. pluchei was artificially induced to bounce whenever the predator was near, provided additional evidence that bouncing is effective in defending H. pluchei against web-invaders.     

Out of the Frying Pan and into the Fire: a Novel Trade-Off for Batesian Mimics

A mimicry system was investigated in which the models were ants (Formicidae) and both the mimics and the predators were jumping spiders (Salticidae). By using motionless lures in simultaneous‐presentation prey‐choice tests, how the predators respond specifically to the static appearance of ants and ant mimics was determined. These findings suggest a rarely considered adaptive trade‐off for Batesian mimics of ants. Mimicry may be advantageous when it deceives ant‐averse potential predators, but disadvantageous in encounters with ant‐eating specialists. Nine myrmecophagic (ant‐eating) species (from Africa, Asia, Australia and North America) and one araneophagic (spider‐eating) species (Portia fimbriata from Queensland) were tested with ants (five species), with myrmecomorphic (ant‐like) salticids (six species of Myrmarachne) and with non‐ant‐like prey (dipterans and ordinary salticids). The araneophagic salticid chose an ordinary salticid and chose flies significantly more often than ants. Portia fimbriata also chose the ordinary salticid and chose flies significantly more often than myrmecomorphic salticids. However, there was no significant difference in how P. fimbriata responded to ants and to myrmecomorphic salticids. The myrmecophagic salticids chose ants and chose myrmecomorphic salticids significantly more often than ordinary salticids and significantly more often than flies, but myrmecophagic salticids did not respond significantly differently to myrmecomorphic salticids and ants.     

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.     

Observations of Portia Africana,an araneophagic jumping spider,living together and sharing prey

Abstract

Instances are documented of finding individuals of Portia africana in the field living aggregated in the webs of other spiders, in the nest complexes of other salticids, around solitary nests of other salticids, and around the nests of oecobiid spiders. Aggregation members included all active juvenile stages of P. africana, as well as adult males and females. More than one individual of P. africana sometimes fed on the same prey. Small juveniles of P. africana were more often than other stages found aggregated and more often observed feeding together. Small juveniles of P. africana surrounded the nests occupied by other salticid genera and nests occupied by oecobiid spiders. When the resident salticid or oecobiid attempted to leave or enter the nest, one of the P. africana juveniles lunged and captured it, after which other P. africana individuals sometimes joined to feed.     

The biology of Portia fimbriata, a web-building jumping spider (Araneae, Salticidae) from Queensland: intraspecific interactions

Portia fimbriata (Doleschall) is an unusual salticid because it spins webs and uses its own webs and those of other species in predation. However, the courtship and threat displays of this species are more like those of typical, cursorial salticids than like typical web-building spiders. During male-female interactions, males perform leg-waving and leg-shaking displays, with legs I and II extended stiffly forward, while distant from the females. Before mounting they tap the females with their legs; and after mounting they tap, scrape and stroke the females' abdomens. Copulation takes place on or near the female's web or on the webs of other species. Hunched-legs displays, with legs I–III highly flexed and held to the side of the body, occur in male-male interactions. Also, during male-female and female-female interactions, females perform hunched-legs displays, strike, charge, ram, embrace, grapple with and leap at conspecifics. Sometimes they lose legs while grappling. After female-female interactions associated with maternal webs, if the resident decamps, the intruder eats the eggs left behind on a suspended leaf, spins a new egg-case over the destroyed one, and oviposits. Adult and sub-adult males co-habit in webs with sub-adult females for as long as 48 days and mate when the spiders mature.     

Prey classification by an araneophagic ant-like jumping spider (Araneae: Salticidae)

What to attack is one of the most basic decisions predators must make, and these decisions are reliant upon the predator's sensory and cognitive capacity. Active choice of spiders as preferred prey, or araneophagy, has evolved in several distantly related spider families, including jumping spiders (Salticidae), but has never been demonstrated in ant-like jumping spiders. We used prey-choice tests with motionless lures to investigate prey-choice behaviour in Myrmarachne melanotarsa , an East African ant-like salticid that normally lives in aggregations and often associates with other spider species. We show that M . melanotarsa chooses spiders as prey in preference to insects and, furthermore, discriminates between different types of spiders. Myrmarachne melanotarsa 's preferred prey were juvenile hersiliids and its second most preferred were other salticids. To date, all documented examples of araneophagic salticids have been from the basal subfamily Spartaeinae. Myrmarachne melanotarsa is the first non-spartaeine and also the first ant-like salticid for which araneophagy has been demonstrated.     

Predator-induced plasticity in web-building behaviour

Many orb-web weaving spiders add conspicuous silken structures, called stabilimenta, to the hub of their webs, which are hypothesized to attract more prey. However, they may also attract predators. Orb spiders should therefore alter their web-building behaviour to minimize predation risk. We tested this hypothesis by experimentally examining web-building responses of the St Andrew cross spider, Argiope versicolor, to predation risk from one of its natural predators, the jumping spider Portia labiata. We randomly assigned A. versicolor juveniles to one of three treatments: (1) blank control (clean blotting paper: no odour from the predator or nonpredator); (2) predator odour cues from P. labiata; and (3) nonpredator control (odour cues from Leucauge decorata). Each individual of A. versicolor was monitored until it had built five consecutive webs (two webs before and three webs after the introduction of predator cues). When exposed to predator cues, the juveniles not only decreased the frequency of stabilimentum building but also refrained from increasing stabilimentum area, capture area and capture silk thread with subsequent webs compared with the blank control and the nonpredator control. Web-building traits, however, were not significantly different between the blank control and the nonpredator control. One plausible explanation is that A. versicolor juveniles can detect and discriminate between predators and nonpredators through olfactory cues and alter stabilimentum building and other web traits in response to the risk of predation. This is the first demonstration of an adaptive, plastic web-building behavioural response induced by chemical cues from a predator.     

Risk Sensitivity and the Paradox of Colonial Web-Building in Spiders

Group foraging is rare in spiders, occurring only where preyavailability is high. If colonial web-building increases individualprey capture rates as shown, why does group foraging not occurmore often where prey are scarce? Risk sensitivity may explainthis paradox, as variance in prey capture is reduced in groups;risk-averse spiders should join groups only when prey exceeda threshold level. Field studies show that group foraging variesas predicted between species, between populations of a singlespecies, and between sites within a population. However, recentmodels suggest the necessity of examining variance within individualsover time rather than between individuals within populations.Additionally, mechanisms responsible for variance reductionin colonial webs may be less effective than previously assumed.New field data suggest that while prey variance over time maybe somewhat less for individual spiders in groups than for solitaries,the relationship between colonial web-building and variancein prey capture is far more complex than originally thought.The influence of risk sensitivity on reproductive success andthe evolution of colonial web-building is discussed.     

Predator–Prey Interactions Between Aggressive-Mimic Jumping Spiders (Salticidae) and Araneophagic Spitting Spiders (Scytodidae) from the Philippines

In Los Baños in the Philippines (Laguna, Luzon), Scytodes sp. indet. is a web-building spitting spider (Scytodidae) that preys primarily on jumping spiders (Salticidae) and Portia labiata is an aggressive-mimic jumping spider that preys especially frequently on Scytodes. Tactics by which three species of Portia (P. africana, P. fimbriata, and P. labiata) and, for Portia labiata, three disjunct populations (Sri Lanka and, in the Philippines, Sagada and Los Baños) capture this especially dangerous prey are compared. Local adaptation to Scytodes by the Los Baños P. labiata is discussed. The Los Baños P. labiata uniquely made consistent use of tactics (soft plucking with palps and signal–detour–leap sequences) that were apparently responsible for greater prey-capture success and more effective avoidance of being spat on. Inter- and intraspecific differences were evident despite having used Portia that were reared in the laboratory with no prioir experience with scytodids.     

蛛网结构性能及其适应性

蛛网是蜘蛛的捕食工具,蛛网的结构性能不仅影响蜘蛛的捕食效率,也关系着蜘蛛的捕食投入。在不同的内外环境条件影响下,蜘蛛会通过蛛网结构性能上的相应变化来调整捕食策略和维持网结构的稳定性。本文主要综述了蛛网的结构性能以及蜘蛛通过蛛网结构性能表现出的对环境因子的适应性。     

Management intensity and vegetation complexity affect web-building spiders and their prey

Agricultural management and vegetation complexity affect arthropod diversity and may alter trophic interactions between predators and their prey. Web-building spiders are abundant generalist predators and important natural enemies of pests. We analyzed how management intensity (tillage, cutting of the vegetation, grazing by cattle, and synthetic and organic inputs) and vegetation complexity (plant species richness, vegetation height, coverage, and density) affect rarefied richness and composition of web-building spiders and their prey with respect to prey availability and aphid predation in 12 habitats, ranging from an uncut fallow to a conventionally managed maize field. Spiders and prey from webs were collected manually and the potential prey were quantified using sticky traps. The species richness of web-building spiders and the order richness of prey increased with plant diversity and vegetation coverage. Prey order richness was lower at tilled compared to no-till sites. Hemipterans (primarily aphids) were overrepresented, while dipterans, hymenopterans, and thysanopterans were underrepresented in webs compared to sticky traps. The per spider capture efficiency for aphids was higher at tilled than at no-till sites and decreased with vegetation complexity. After accounting for local densities, 1.8 times more aphids were captured at uncut compared to cut sites. Our results emphasize the functional role of web-building spiders in aphid predation, but suggest negative effects of cutting or harvesting. We conclude that reduced management intensity and increased vegetation complexity help to conserve local invertebrate diversity, and that web-building spiders at sites under low management intensity (e.g., semi-natural habitats) contribute to aphid suppression at the landscape scale.     

Contrasting responses of web-building spiders to deer browsing among habitats and feeding guilds

We examined web-building spider species richness and abundance in forests across a deer density gradient to determine the effects of sika deer browsing on spiders among habitats and feeding guilds. Deer decreased the abundance of web-building spiders in understory vegetation but increased their abundance in the litter layer. Deer seemed to affect web-building spiders in the understory vegetation by reducing the number of sites for webs because vegetation complexity was positively correlated with spider density and negatively correlated with deer density. In contrast, the presence of vegetation just above the litter layer decreased the spider density, and deer exerted a negative effect on this vegetation, possibly resulting in an indirect positive effect on spider density. The vegetation just above the litter layer may be unsuitable as a scaffold for building webs if it is too flexible to serve as a reliable web support, and may even hinder spiders from building webs on litter. Alternatively, the negative effect of this vegetation on spiders in the litter may be as a result of reduced local prey availability under the leaves because of the reduced accessibility of aerial insects. The response to deer browsing on web-building spiders that inhabit the understory vegetation varied with feeding guild. Deer tended to affect web-invading spiders, which inhabit the webs of other spiders and steal prey, more heavily than other web-building spiders, probably because of the accumulated effects of habitat fragmentation through the trophic levels. Thus, the treatment of a particular higher-order taxon as a homogeneous group could result in misleading conclusions about the effects of mammalian herbivores.     

The hunting-web of the young spider Pisaura mirabilis

In the Pisauridae both web-building and non web-building spiders are present, the former building webs comparable to the funnel-webs of the Agelenidae.
Pisaura mirabilis has always been described as a non web-building spider catching the prey by sight.
However the sexually immature Pisaura mirabilis has been found to build a web in which the animal sits.
The structure of this web is not directly comparable to any other type of web, but some kind of relationship to the funnel-web of the Agelenidae may exist.
Even if the young Pisaura mirabilis is capable of catching prey without using the web, detection of the prey seems to be a main function of this structure.     

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.