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.     

Aggressive use of Batesian mimicry by an ant-like jumping spider

Batesian and aggressive mimicry are united by deceit: Batesian mimics deceive predators and aggressive mimics deceive prey. This distinction is blurred by Myrmarachne melanotarsa, an ant-like jumping spider (Salticidae). Besides often preying on salticids, ants are well defended against most salticids that might target them as potential prey. Earlier studies have shown that salticids identify ants by their distinctive appearance and avoid them. They also avoid ant-like salticids from the genus Myrmarachne. Myrmarachne melanotarsa is an unusual species from this genus because it typically preys on the eggs and juveniles of ant-averse salticid species. The hypothesis considered here is that, for M. melanotarsa, the distinction between Batesian and aggressive mimicry is blurred. We tested this by placing female Menemerus sp. and their associated hatchling within visual range of M. melanotarsa, its model, and various non-ant-like arthropods. Menemerus is an ant-averse salticid species. When seeing ants or ant mimics, Menemerus females abandoned their broods more frequently than when seeing non-ant-like arthropods or in control tests (no arthropods visible), as predicted by our hypothesis that resembling ants functions as a predatory ploy.     

Compound mimicry and trading predators by the males of sexually dimorphic Batesian mimics

Sexual dimorphism is pronounced in Myrmarachne, a large genus of ant-like jumping spiders (Salticidae) and one of the major animal groups in which Batesian mimicry of ants has evolved. Although adult females and juveniles of both sexes are distinctly ant-like in appearance, Myrmarachne males have elongated chelicerae that might appear to detract from their resemblance to ants. Experimental findings suggest that the Myrmarachne male's solution is to adopt compound mimicry (i.e. the male's model seems to be not simply an ant worker but a combination of an ant and something carried in the ant's mandibles: an "encumbered ant"). By becoming a mimic of a particular subset of worker ants, Myrmarachne males may have retained their Batesian-mimicry defence against ant-averse predators, but at the price of receiving the unwanted attention of predators for which encumbered ants are preferred prey. Two salticid species were used as predators in the experiments. Portia fimbriata is known to choose other salticids as preferred prey and to avoid unencumbered ants and their mimics (Myrmarachne females). In experiments reported here, P. fimbriata avoided encumbered ants and Myrmarachne males. Ants are the preferred prey of Chalcotropis gulosus. In our experiments, C. gulosus chose safer encumbered ants in preference to more dangerous unencumbered ants, chose Myrmarachne males more often than Myrmarachne females and showed no evidence of distinguishing between Myrmarachne males and encumbered ants. The cost of reconciling sexual dimorphism with Batesian mimicry appears to be that Myrmarachne males attract the unwanted attention of specialist predators of their compound model.     

Salticid predation as one potential driving force of ant mimicry in jumping spiders

Many spiders possess myrmecomorphy, and species of the jumping spider genus Myrmarachne exhibit nearly perfect ant mimicry. Most salticids are diurnal predators with unusually high visual acuity that prey on various arthropods, including conspecifics. In this study, we tested whether predation pressure from large jumping spiders is one possible driving force of perfect ant mimicry in jumping spiders. The results showed that small non-ant-mimicking jumping spiders were readily treated as prey by large ones (no matter whether heterospecific or conspecific) and suffered high attack and mortality rates. The size difference between small and large jumping spiders significantly affected the outcomes of predatory interactions between them: the smaller the juvenile jumping spiders, the higher the predation risk from large ones. The attack and mortality rates of ant-mimicking jumping spiders were significantly lower than those of non-ant-mimicking jumping spiders, indicating that a resemblance to ants could provide protection against salticid predation. However, results of multivariate behavioural analyses showed that the responses of large jumping spiders to ants and ant-mimicking salticids differed significantly. Results of this study indicate that predation pressure from large jumping spiders might be one selection force driving the evolution of nearly perfect myrmecomorphy in spiders and other arthropods.     

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.     

The biology of ant-like jumping spiders: intraspecific interactions of Myrmarachne lupata (Araneae, Salticidae)

Myrmarachne lupata is an ant-like salticid in which males have very large chelicerae. The display repertoire of this species is unusually large and complex for a salticid spider. Each individual male uses one of three different mating tactics depending on the female's maturity and location. With adult females outside nests type 1 courtship occurs which seems to be a form of visual communication and includes specialized movements and postures of the legs, palps and body. With adult females inside nests, males use type 2 courtship, which seems to be a form of non-visual communication and consists primarily of probing with the legs on the silk; males mate with receptive females inside the nests. With subadult females, males first use type 2 courtship then spin an adjacent silken chamber and cohabit. After she moults and matures, mating occurs inside the nest. Vacant nests of conspecific females, but not those of another sympatric salticid species, elicit courtship behaviour from males. During male-male interactions, embracing occurs with the large chelicerae spread apart. Females and subadults also display, and different displays occur in interactions depending on the sex/age classes of the spiders involved. Despite the unusual morphology of these spiders, their individual displays are similar to those of more typical salticids. During copulation males stand beside the female instead of over or on her as occurs with typical salticids.     

Vision-based innate aversion to ants and ant mimics

Innate vision-based aversions to model and mimic were investigatedusing a mimicry system in which the models were ants (Formicidae),and both the mimics and the predators were jumping spiders (Salticidae).Jumping spiders are a large group of predatory invertebratesthat usually prey opportunistically on prey of similar size.We used 12 representative species from this group, the "ordinarysalticids" as predators. The mimics considered belonged to anothergroup, salticids that resemble ants. A choice arena containingan empty chamber and a stimulus chamber was used for testingpredator responses to a variety of dead arthropods (ants, antmimics, and an array of non–ant-like species) mountedin a lifelike posture. When presented with visual cues fromarthropods other than ants or ant-like salticids, naive predatorschose the empty chamber no more often than the stimulus chamber.However, when visual cues were from ants or from ant-like salticids,ordinary salticids chose the empty chamber significantly moreoften than the stimulus chamber. These findings suggest learningby the predator is not necessary in order for ant-like salticidsto gain Batesian mimicry advantages.     

Innate aversion to ants (Hymenoptera: Formicidae) and ant mimics: experimental findings from mantises (Mantodea)

Field data suggest that ants may be important predators of mantises which, in turn, may be important predators of jumping spiders (Salticidae). Using a tropical fauna from the Philippines as a case study, the reactions of mantises to ants, myrmecomorphic salticids (i.e. jumping spiders that resemble ants) and ordinary salticids (i.e. jumping spiders that do not resemble ants) were investigated in the laboratory. Three mantis species ( Loxomantis sp., Orthodera sp., and Statilia sp.) were tested with ten ant species, five species of Myrmarachne (i.e. myrmecomorphic salticids), and 23 ordinary salticid species. Two categories of the myrmecomorphic salticids were recognized: (1) 'typical Myrmarachne ' (four species with a strong resemblance to ants) and (2) Myrmarachne bakeri (a species with less strong resemblance to ants). Ants readily killed mantises in the laboratory, confirming that, for the mantises studied, ants are dangerous. In alternate-day testing, the mantises routinely preyed on the ordinary salticids, but avoided ants. The mantises reacted to myrmecomorphic salticids similarly to how they reacted to ants (i.e. myrmecomorphic salticids appear to be, for mantises, Batesian mimics of ants). Although myrmecomorphic salticids were rarely eaten, M . bakeri was eaten more often than typical Myrmarachne . Because the mantises had no prior experience with ants, ant mimics or ordinary salticids, our findings suggest that mantises have an innate aversion to attacking ants and that this aversion is generalized to myrmecomorphic salticids even in the absence of prior experience with ants. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 23–32.     

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.     

Extreme ultraviolet sexual dimorphism in jumping spiders (Araneae: Salticidae)

Jumping spiders (Salticidae) have acute vision with some cells in the retina that are sensitive to ultraviolet (UV) spectra (< 400 nm). However, no study has documented the use of UV signals in salticids. To appreciate the function of UV vision, it is necessary to characterize the UV colours of salticids. In the present study, the UV and human-visible wavelengths of a tropical ornate salticid spider, Cosmophasis umbratica , were analysed using reflectance spectrometry to obtain evidence of sex-specific UV colours. An absolute sexual dimorphism in the UV colours of this salticid species was found. All of the body parts of adult males that are displayed to conspecifics during intra-specific interactions reflected UV (300–400 nm) light, whereas the adult females and juveniles did not reflect UV light from any body part. A great deal of variation was also found in the UV wavebands among males. This is the first full UV characterization of a salticid spider and the first study to demonstrate an extreme sexual UV dimorphism in jumping spiders. The findings obtained provide evidence that UV reflectance may comprise important sexual signals in jumping spiders.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 397–406.     

Ant mimicry lessens predation on a North American jumping spider by larger salticid spiders

Ant-like appearance (myrmecomorphy) has evolved >70 times in insects and spiders, accounting for >2,000 species of myrmecomorphic arthropods. Most myrmecomorphic spiders are considered to be Batesian mimics; that is, a palatable spider avoids predation through resemblance to an unpalatable ant-although this presumption has been tested in relatively few cases. Here we explicitly examined the extent to which Peckhamia picata (Salticidae), a North American ant-mimicking jumping spider, is protected from four species of jumping spider predators, relative to nonmimetic salticids and model ants. In addition, we conducted focused behavioral observations on one salticid predator, Thiodina puerpera, to determine the point at which the predators' behaviors toward model, mimic, and nonmimic diverge. We also examined the behaviors of Peckhamia in the presence of Thiodina. We found that mimetic jumping spiders were consumed less than a third as often as nonmimetic jumping spiders, suggesting that Peckhamia does indeed gain protection as a result of its resemblance to ants, and so can be considered a Batesian mimic. Furthermore, our focal predator did not consume any ant-mimicking spiders, and seemed to categorize Peckhamia with its model ant early in the hunting sequence. Such early determination of prey versus nonprey may be the result of speed-accuracy trade-offs in predator decision-making.     

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.     

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.     

Prey-capture techniques and prey preferences of Habrocestum pulex, an ant-eating jumping spider (Araneae, Salticidae) from North America

The prey-catching techniques and prey preferences of Habrocestum pulex (Hentz), ant-eating jumping spider (Araneae: Salticidae) from North America, were studied in the laboratory. H. pulex uses prey-specific, prey-catching behaviour against ants. Ants, but not other insects, were consistently attacked head-on. After attacking an ant, but not after attacking other insects, H. pulex kept its forelegs extended laterally and forwards without touching the ground. H. pulex feeds on ants in preference to other insects. Preference for ants and prey-specific predatory behaviour do not depend on prior experience with ants. As in earlier studies of other ant-eating salticids, three different types of tests for prey preference were carried out, using active, living prey: Type 1 (one type of prey presented to salticid at a time on alternate days); Type 2 (two types of prey presented to salticid simultaneously); and Type 3 (salticid feeding on one type of prey presented with alternative prey of another type). However, newly-designed apparatus made testing more efficient. Preference for ants over other insects is shown not to depend on level of activity or any other cues from prey movement pattern: Type 1 and Type 2 tests were carried out using motionless (dead) lures, and again ants were taken in preference to other insects. Findings from this study are discussed in relation to recent findings on other ant-eating salticids.     

Observations in nature of detouring behaviour by Portia fimbriata, a web-invading aggressive mimic jumping spider from Queensland

Portia fimbriata , a web-invading, araneophagic salticid that uses aggressive mimicry to deceive its prey (web-building spiders), takes indirect routes to reach its prey (i.e. it makes detours). Data are presented from 18 instances of Portia making detours to reach prey in nature, the prey being five different species of web-building spiders. Portia spent 17 min (median) per predatory sequence with the prey out of view and covered 375 mm detouringper sequence. These detours were longer and more complex than those previously recorded for salticids, and these are the first detailed records of detouring behaviour by a salticid in the field.     

Bugs with backpacks deter vision-guided predation by jumping spiders

As a case study of how insects use masks as a defence against vision-guided predators, an experimental study was carried out using Acanthaspis petax , a reduviid bug ('ant bug') that covers itself with a 'mask', or 'backpack', made from carcasses of its preferred prey (ants), and three salticid spider species, Hyllus sp., Plexippus sp. and Thyene sp., salticids being predators with exceptionally acute vision. The ant bugs and the salticids were from the Lake Victoria region of East Africa. In each test, a salticid was presented with a live bug or a lure made from a dead bug, with the mask removed ('naked') or intact ('masked'). Salticids made predatory responses to naked bugs significantly more often than to masked bugs. These findings suggest that salticids readily identify naked bugs as prey, but fail to identify masked bugs as prey.     

The biology of ant-like jumping spiders (Araneae, Salticidae): prey and predatory behaviour of Myrtnarachne with particular attention to M. lupata from Queensland

Myrtnarachne is a genus of ant-like salticids. Eight species were observed feeding, in nature, in Australia, Kenya, Malaysia and Sri Lanka, on varied types of insects but not ants. The behaviour of M. lupata , from Australia, was studied in the laboratory. Predatory sequences were found to differ considerably from those of typical salticids. Attacking by lunging instead of leaping and the pronounced use of pre-attack tapping are especially noteworthy. The unusual behaviour of M. lupata when preying on insects is consistent with maintenance of ant mimicry. Myrmarachne lupata also preys on the eggs of other spiders which it extracts from their nests. The males of many species have very large chelicerae, and the large chelicerae of M. lupata males influence the course of predatory sequences, with insects and with eggs.     

Anti-predator crèches and aggregations of ant-mimicking jumping spiders (Araneae: Salticidae)

Myrmarachne assimilis , an ant-like jumping spider (Araneae, Salticidae) from the Philippines and a Batesian mimic of Oecophylla smaragdina , the Asian weaver ant, aggregates on leaves in the company of its model. All stages in this species' lifecycle are sometimes found in nest complexes (nests connected to each other by silk). Although aggregating and forming nest complexes is known for a few other salticid species, the aggregations of M. assimilis have some unusual characteristics. In particular, reproductive females appear to be most frequently found with other reproductive females in nest complexes, suggesting that nest complexes have a role in parental care and are often built by females joining other females. An egg-survival experiment showed that eggs in solitary nests were more often destroyed than were eggs in nest complexes, suggesting that, for females of M. assimilis , choosing aggregations as oviposition sites may be functionally akin to life insurance for their progeny.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 475–481.     

Vision-based ability of an ant-mimicking jumping spider to discriminate between models,conspecific individuals and prey

Myrmarachne assimilis, an ant-like (myrmecomorphic) jumping spider (Araneae, Salticidae) from the Philippines, is a Batesian mimic of Oecophylla smaragdina, the Asian weaver ant. Salticids are well known for their acute eyesight and the elaborate vision-based display behaviour they adopt during encounters with conspecific individuals, but most salticids are not myrmecomorphic. Despite its unusual morphology, M. assimilis adopts display behaviour during intraspecific interactions that is similar to the display behaviour of more typical salticids. The specificity with which M. assimilis deploys display behaviour is investigated and provides insights into this mimic’s ability to differentiate, by sight alone, between models, conspecific individuals and prey. During each standardized test, an adult M. assimilis female was in a large cage along with a small transparent glass vial, a stimulus animal being enclosed in the vial such that potential optical cues, but not potential chemical cues, were available to the tested M. assimilis individual. Depending on the test, the stimulus animal was another adult M. assimilis female, a house fly (prey) or an ant (Camponotus sp. or O. smaragdina). Only the conspecific female consistently elicited display from M. assimilis, implying that M. assimilis is a Batesian mimic that can, when relying on vision alone, discriminate between conspecific individuals, models and prey. Received 12 June 2006; revised 22 September 2006; accepted 26 September 2006.     

A specialized araneophagic predator's short‐term nutrient utilization depends on the macronutrient content of prey rather than on prey taxonomic affiliation

A specialist predator that has a specialized diet, prey‐specific prey‐capture behaviour and a preference for a particular type of prey may or may not be specialized metabolically. Previous studies have shown that jumping spiders of the genus Portia prey on other spiders using prey‐specific prey‐capture behaviour, prefer spiders as prey to insects and gain long‐term benefits in terms of higher survival and growth rates on spider diets than on insect diets. However, it is unclear whether there are substances uniquely present in spiders on which Portia depends, or, alternatively, spiders and insects all contain more or less the same nutrients but the relative amounts of these substances are such that Portia perform better on a spider diet. These questions are addressed by testing the hypothesis that prey specialization includes metabolic adaptations that allow Portia an enhanced nutrient extraction or nutrient utilization efficiency when feeding on spider prey compared with insect prey. Three groups of Portia quei Zabka are fed either their preferred spider prey or one of two types of flies (Drosophila melanogaster Meigen) that differ in nitrogen and lipid content. Portia quei shows a higher feeding rate of high‐protein flies than of high‐lipid flies and spiders but, after 5 days of feeding, there is no significant difference in growth between treatments, and the diets lead to significant changes in the macronutrient composition of P. quei as a result of variable extraction and utilization of the prey. The short‐term utilization of spider prey is similar to that of high‐lipid flies and both differ in several respects from the utilization of high‐protein flies. Thus, the short‐term nutrient utilization is better explained by prey macronutrient content than by whether the prey is a spider or not. The results suggest that spider prey may have a more optimal macronutrient composition for P. quei and that P. quei does not depend on spider‐specific substances.