Araneophagic Spider Research Articles

First record of Gardena melinarthrum (Heteroptera: Reduviidae) from Thailand with a note on its predation of an araneophagic spider

The thread-legged assassin bug Gardena melinarthrum Dohrn, 1860 (Heteroptera: Reduviidae) is reported for the first time from Thailand. Morphological data of the female adult, including detailed information of the genitalia, is provided with photographs. We also report the predation of an araneophagic spider Portia sp. (Araneae: Salticidae) by the bug in a spider’s web. It is the occasional observation of intra-guild predation evidence involving an assassin bug (Hemiptera: Reduviidae: Gardena melinarthrum) and a spider (Araneae: Salticidae: Portia sp.) in a riparian habitat.

Offspring mortality factors and parental care efficiency of the spider Manogea porracea (Araneidae) in the Brazilian savanna

The expressions of parental care can vary in space and time because factors driving offspring mortality depend on variable abiotic and biotic conditions. Manogea porracea is a spider that exhibits biparental care and widespread distribution in the Neotropical region. Parents can protect their offspring against abiotic conditions that may damage their webs, or compromise their egg sacs, and against araneophagic spiders that prey on their eggs. However, the current knowledge of the parental care in the species is restricted to a population located in areas covered by Eucalyptus plantations. This study investigates parental care efficiency in a new ecological context, a protected area of Brazilian savanna. We described the substrates in which M. porracea built webs and the agents of egg mortality. We also performed a parent removal experiment to test the effect of parental care on the integrity of nursery webs, offspring survival, and the presence of egg predators. Spiders built webs at variable heights and many distinct substrates but were mainly associated with the bromeliad Ananas ananassoides. We found two previously reported egg predators, Faiditus caudatus and Argyrodes elevatus (Araneae Theridiidae), and a new one emerging from the egg sacs, the insect Zeugomantispa virescens (Neuroptera Mantispidae). The presence of parents in the webs of M. porracea prevented the webs from collapsing and effectively increased offspring survival. However, the occurrence of egg predators was not reduced by the presence of parents. Overall, parental care increased offspring survival in both populations, but variation in biotic and abiotic factors between areas influenced offspring mortality and the efficiency of parental behaviours. Our results emphasise the importance of investigating multiple populations in behavioural studies of parental care.

The ontogenetic dietary shift from non-dangerous to dangerous prey in predator-eating predators under capture risk.

Evaluating the patterns and generality of ontogenetic dietary shifts (ODSs) contributes to understanding prey-predator interactions and food web dynamics. Numerous studies have focused on predators that target distinctively lower trophic-level organisms. However, the ODS of predators that routinely prey on organisms at similar trophic levels (i.e., predator-eating predators) have been neglected in ODS research. The ODS patterns of predator eaters may not fit into conventional frameworks owing to constraints of potential capture risk (e.g., deadly counterattack from prey) and body size. We aimed to reveal the ODS patterns of predator eaters and determine whether the patterns were affected by body size and capture risk. Assuming that capture risk is a significant factor in ODS patterns, we expected: (1) juvenile araneophagic spiders to forage on non-dangerous prey (insects) and capture larger non-dangerous prey more frequently than dangerous prey (spiders); and (2) as they grow, their prey types will shift from non-dangerous to dangerous prey because larger predators will be able to capture dangerous prey as the optimal food. As a result of field observations, we revealed that the major ODS pattern in these spiders changed from a mixed (both insect and spider) to a spider-dominant diet. The model selection approach showed that this diet shift was partly due to predator size, and the relative importance of predator size was higher than the life stage per se and almost equal to species identity. In these spiders, the body size of spider prey tended to be smaller than that of insects when the predators were small, suggesting that capture risk may be a critical factor in determining the ODS patterns of these predators. Therefore, our study adds to the evidence that the capture risk is crucial in comprehensively understanding the mechanisms determining ODS patterns in natural systems.

Araneophagy as an alternative foraging tactic to kleptoparasitism in two Argyrodinae (Araneae: Theridiidae) species

Kleptoparasitism is assumed to be the main foraging strategy in some animal groups, such as the spiders of the subfamily Argyrodinae (Theridiidae). However, some species may also feed on silk threads, egg sacs, or even their hosts. The conditions determining these alternative foraging tactics remain unknown for most species. We performed field observations, stable isotope analysis and laboratory experiments to investigate kleptoparasitism and araneophagy of Argyrodes elevatus and Faiditus caudatus in webs of Manogea porracea (Araneidae). We evaluated the following hypotheses: (1) both species exhibit higher trophic positions than their hosts and closest to an araneophagic sympatric species; (2) host web selection is influenced by the presence of alternative resources (adult male and female, and egg sacs); and (3) they preferentially consume egg sacs instead of stored prey items. Both argyrodines showed higher trophic positions than their female hosts and closest to an araneophagic spider species. The invaders were found mainly on host webs with one adult and egg sacs and with egg sacs only. Finally, A. elevatus preferred to feed on prey captured by the host spider instead of egg sacs. We discussed the factors that can potentially determine the choices between foraging exclusively as kleptoparasites and consuming the hosts.

Nest usurpation: a specialised hunting strategy used to overcome dangerous spider prey

Hunting other predators is dangerous, as the tables can turn and the hunter may become the hunted. Specialized araneophagic (spider eating) predators have evolved intriguing hunting strategies that allow them to invade spiders’ webs by adopting a stealthy approach or using aggressive mimicry. Here, we present a newly discovered, specialized hunting strategy of the araneophagic spider Poecilochroa senilis (Araneae: Gnaphosidae), which forces its way into the silk retreat of the potential spider prey and immobilizes it by swathing gluey silk onto its forelegs and mouthparts. Poecilochroa senilis has been reported from the nests of a several, often large, spider species in the Negev desert (Israel), suggesting specialization on spiders as prey. Nevertheless, in laboratory experiments, we found that P. senilis has a wider trophic niche, and fed readily on several small insect species. The specialized nest-invading attack was used more frequently with large spiders, and even small juvenile P. senilis were able to attack and subdue larger spiders. Our observations show that specific hunting tactics, like nest usurpation, allow specialized predators to overcome defences of dangerous prey.

Comparative study of spinning field development in two species of araneophagic spiders (Araneae, Mimetidae, Australomimetus)

External studies of spider spinning fields allow us to make inferences about internal silk gland biology, including what happens to silk glands when the spider molts. Such studies often focus on adults, but juveniles can provide additional insight on spinning apparatus development and character polarity. Here we document and describe spinning fields at all stadia in two species of pirate spider (Mimetidae: Australomimetus spinosus, A. djuka). Pirate spiders nest within the ecribellate orb-building spiders (Araneoidea), but are vagrant, araneophagic members that do not build prey-capture webs. Correspondingly, they lack aggregate and flagelliform silk glands (AG, FL), specialized for forming prey-capture lines in araneoid orb webs. However, occasional possible vestiges of an AG or FL spigot, as observed in one juvenile A. spinosus specimen, are consistent with secondary loss of AG and FL. By comparing spigots from one stadium to tartipores from the next stadium, silk glands can be divided into those that are tartipore-accommodated (T-A), and thus functional during proecdysis, and those that are not (non-T-A). Though evidence was more extensive in A. spinosus, it was likely true for both species that the number of non-T-A piriform silk glands (PI) was constant (two pairs) through all stadia, while numbers of T-API rose incrementally. The two species differed in that A. spinosus had T-A minor ampullate and aciniform silk glands (MiA, AC) that were absent in A. djuka. First instars of A. djuka, however, appeared to retain vestiges of T-AMiA spigots, consistent with a plesiomorphic state in which T-AMiA (called secondary MiA) are present. T-AAC have not previously been observed in Australomimetus and the arrangement of their spigots on posterior lateral spinnerets was unlike that seen thus far in other mimetid genera. Though new AC and T-API apparently form throughout much of a spider’s ontogeny, recurring spigot/tartipore arrangements indicated that AC and PI, after functioning during one stadium, were used again in each subsequent stadium (if non-T-A) or in alternate subsequent stadia (if T-A). In A. spinosus, sexual and geographic dimorphisms involving AC were noted. Cylindrical silk gland (CY) spigots were observed in mid-to-late juvenile, as well as adult, females of both species. Their use in juveniles, however, should not be assumed and only adult CY spigots had wide openings typical of mimetids. Neither species exhibited two pairs of modified PI spigots present in some adult male mimetids.

Molecular phylogenetic analysis of "pirate spiders" (Araneae, Mimetidae) with the description of a new African genus and the first report of maternal care in the family.

We investigate the phylogeny of "pirate spiders" (Mimetidae), a family of araneophagic spiders known for their use of aggressive mimicry as a foraging strategy, but poorly understood phylogenetically. Relationships are inferred by including molecular data from six loci for 92 mimetid terminals spanning four genera, and 119 outgroups representing 12 families. Phylogenetic analyses based on parsimony, maximum-likelihood and Bayesian approaches, as well as static and dynamic homology, robustly support monophyly of Mimetidae and a sister-group relationship to a clade comprising Tetragnathidae+Arkyidae. Relationships among the mimetid genera are largely congruent across methods, as follows: (Gelanor (Ero (Anansi n. gen. (Australomimetus, Mimetus)))). Diversification of Mimetidae is estimated to be around 114Ma, in the Early Cretaceous. In light of the results of our phylogenetic analyses, we erect Anansi n. gen. to include a clade of mimetids from West Africa that contains at least four species, including the newly described A.luki n. sp. We present the first report of maternal care in Mimetidae based on novel field observations.

Maternal defensive behaviors of Uloborus sp. (Araneae, Uloboridae): behavioral repertoire and influence of clutch size and female size on female aggressiveness

Maternal care in spiders often involves behaviors associated with the protection of eggs and spiderlings against parasitoids and predators (including conspecifics). The females of several species have been documented to move their egg sacs away from natural enemies or to invest in active defense behaviors against web invaders, such as parasitoid wasps or araneophagic spider species, to protect their brood. In this study, we present observations of protective behavior by Uloborus sp. females carrying egg sacs. We also investigated whether brood size and female size influence female aggressive behaviors and response time against an artificial source of disturbance. Females carrying egg sacs almost immediately perceived and reacted aggressively against the artificial stimulus, whereas females without egg sacs moved away or ran to the web margins, avoiding the source of disturbance. The aggressive response was independent of clutch size and female body size, indicating that all females will risk interacting with potential agents of egg mortality. This systematic response by all females with egg sacs may be important for reducing the incidence of attack by the egg predator wasp Bathyzonus sp. (Ichneumonidae).

The role of numerical competence in a specialized predatory strategy of an araneophagic spider

Although a wide range of vertebrates have been considered in research on numerical competence, little is known about the role of number-related decisions in the predatory strategies of invertebrates. Here, we investigate how numerical competence is expressed in a highly specialized predatory strategy adopted by the small juveniles of Portia africana when practicing communal predation, with the prey being another spider, Oecobius amboseli. Two or more P. africana juveniles sometimes settle by the same oecobiid nest and then share the meal after one individual captures the oecobiid. Experiments were designed to clarify how these predators use number-related cues in conjunction with non-numerical cues when deciding whether to settle at a nest. We used lures (dead spiders positioned in lifelike posture) arranged in a series of 24 different scenes defined by the type, configuration and especially number of lures. On the whole, our findings suggest that P. africana juveniles base settling decisions on the specific number of already settled conspecific juveniles at the nest and express a preference for settling when the number is one instead of zero, two or three. By varying the size of the already settled juveniles and their positions around the nest, we show that factors related to continuous variables and stimulus configuration are unlikely explanations for our findings.

Kleptoparasites: a twofold cost of group living for the colonial spider, Metepeira incrassata (Araneae, Araneidae)

Several species of kleptoparasitic and araneophagic spiders (Araneae: Family Theridiidae, Subfamily Argyrodinae) are found in colonial webs of the orb-weaving spider Metepeira incrassata (Araneae, Araneidae) from Mexico, where they steal food and/or prey upon their spider hosts. Census data from natural M. incrassata colonies reveal that the incidence of these species increases with colony size. This pattern may reflect the presence of several other orb-weaving spiders, each with their own kleptoparasitic species, invading larger M. incrassata colonies. As the number of these associated spiders increases, so does the density and number of Argyrodinae species in M. incrassata colonies, suggesting that associated spiders might reduce their own kleptoparasite load by building their webs within M. incrassata colonies. This represents a twofold cost to M. incrassata, as a field enclosure experiment revealed that a primarily kleptoparasitic species (Argyrodes elevatus) may reduce prey available to their hosts, but a kleptoparasitic/araneophagic species (Neospintharus concisus) inflicts high mortality upon M. incrassata. However, the cost of kleptoparasitism and predation by these species may be offset in part for M. incrassata individuals in large colonies by certain defensive mechanisms inherent in groups, i.e., “attack-abatement” and “selfish herd” effects. We conclude that increased occurrence of kleptoparasitic and/or predatory Argyrodinae spiders is a consequence of colonial web building and is an important potential cost of group living for colonial web-building spiders.

SPECIALISED PREDATION BY PALPIMANUS SP. (ARANEAE: PALPIMANIDAE) ON JUMPING SPIDERS (ARANEAE: SALTICIDAE)

This is the first detailed report on the natural prey and the prey-capture tactics of Palpimanus sp. from Entebbe (Uganda). Although this species fed occasionally on insects, its dominant prey in the field was other spiders, especially jumping spiders (Salticidae) and their eggs. Encounters between Palpimanus sp. and salticids were staged in the laboratory under red light (to simulate nocturnal or dimly-lit conditions) and under white light (i.e. full light, to simulate daylight or brightly-lit conditions). Altering ambient lighting had no discernible effect on the palpimanid’s predatory tactics, suggesting that eyesight has little, if any role, in governing the palpimanid’s prey-capture behaviour. Reliance on stealth appeared to be critical in enabling the palpimanid to avoid detection and to succeed at capturing salticids. The prey-capture tactics of Palpimanus sp. are compared to the tactics used by other araneophagic spiders to capture salticids.

One-encounter search-image formation by araneophagic spiders.

An experimental study of search-image use by araneophagic jumping spiders (i.e., salticid spiders that prey routinely on other spiders) supports five conclusions. First, araneophagic salticids have an innate predisposition to form search images for specific prey from their preferred prey category (spiders) rather than for prey from a non-preferred category (insects). Second, single encounters are sufficient for forming search images. Third, search images are based on selective attention specifically to optical cues. Fourth, there are trade-offs in attention during search-image use (i.e., forming a search image for one type of spider diminishes the araneophagic salticid's attention to other spiders). Fifth, the araneophagic salticid's adoption of search images is costly to the prey (i.e., when the araneophagic salticid adopts a search, the prey's prospects for surviving encounters with the araneophagic salticid are diminished). Cognitive and ecological implications of search-image use are discussed.

AFRARCHAEA GRIMALDII, A NEW SPECIES OF ARCHAEIDAE (ARANEAE) IN CRETACEOUS BURMESE AMBER

Abstract Afrarchaea grimaldii new species (Archaeidae, Archaeinae) from 88–95 Ma (Cenomanian–Turonian) Upper Cretaceous amber (Burmite) from Myanmar (Burma) is described. This is the first spider to be described from this deposit and is the oldest known Archaeidae sensu stricto extending the known range of the family by approximately 50 Ma from the previously oldest recorded specimens in Baltic and Bitterfeld ambers, and provides further evidence that spiders were not severely affected by the end-Cretaceous mass extinction event. It represents the oldest fossil record of an araneophagic spider. This species could be used to argue for both the theory of mobilistic biogeography and ousted relicts to explain the zoogeography of the genus, but until new data become available, supports neither reliably.

Diet and Insectivory in the “Araneophagic” Spider, Mimetus notius (Araneae: Mimetidae)

Abstract Data on the diet of the web-invading spider Mimetus notius were collected to determine the diet of this araneophagic spider. Mimetus notius primarily invades Theridiidae and Aaraneidae webs and is capable of preying upon at least seven families of spiders, principally in the genus Theridion (Araneae: Theridiidae). Mimetus notius invades the webs of several species on which no successful predation was observed. These data provide the first field data showing significant insectivory by a web invading mimetid, constituting 29% of the prey in this study. The presence of insects in the diet provides a potential explanation for the invasion of webs where successful predation on the resident is unlikely.

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.

Olfactory cues from conspecifics inhibit the web-invasion behavior of Portia, web-invading araneophagic jumping spiders (Araneae: Salticidae)

Portia is a genus of web-invading araneophagic spiders that use aggressive mimicry to capture their spider prey. In an experimental study, we demonstrate that adult females of Portia africana, P. fimbriata, P. labiata, and P. schultzi produce olfactory cues that affect the behavior of conspecific adult males, adult females, and juveniles. The olfactory cues of Portia spp. inhibit aggressive mimicry of conspecific spiders that are on a prey spider's web even if the prey spider is visible. This inhibition occurs regardless of the prey spider's web geometry. Prey pursuit by Portia is also inhibited when conspecific females provide olfactory cues in cases where the prey is a spider inhabiting a web. Olfactory cues from adult females elicit courtship displays of conspecific males when males are on the prey spider's web. Portia spp. do not alter their behavior when exposed to olfactory cues of heterospecifics.

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.