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PubMed2002

Spider phobia interaction of disgust and perceived likelihood of involuntary physical contact.

After reading vignettes, a group of spider-phobic girls (n = 18) and a group of nonphobic girls (n = 18) rated the subjective probability of spiders entering their private living space, their tendency to approach and make physical contact, and the subjective probability of spiders doing physical harm. In addition, they indicated their eagerness to eat a favorite food item before as well as after it had been shortly contacted by spiders. In support of the idea that spider phobia results from the convergence of spiders' disgusting properties and the subjective probability of involuntary contact, phobic girls reported relatively high ratings concerning: (a) the probability of spiders entering their room; (b) spiders' tendency to approach and make physical contact; and (c) spiders' disgust-evoking status. Finally, regression analysis indicated that spiders' disgust-evoking status is the single best predictor of spider phobia, whereas the independent contribution of the perceived probability of spiders doing physical harm was found to be negligible. All in all, the present findings strongly support the idea that spider phobia essentially reflects a fear of physical contact with a disgusting stimulus.

Adolescent↗

PubMed2006

Intraguild interactions between spiders and ants and top-down control in a grassland food web.

In most terrestrial ecosystems ants (Formicidae) as eusocial insects and spiders (Araneida) as solitary trappers and hunters are key predators. To study the role of predation by these generalist predators in a dry grassland, we manipulated densities of ants and spiders (natural and low density) in a two-factorial field experiment using fenced plots. The experiment revealed strong intraguild interactions between ants and spiders. Higher densities of ants negatively affected the abundance and biomass of web-building spiders. The density of Linyphiidae was threefold higher in plots without ant colonies. The abundance of Formica cunicularia workers was significantly higher in spider-removal plots. Also, population size of springtails (Collembola) was negatively affected by the presence of wandering spiders. Ants reduced the density of Lepidoptera larvae. In contrast, the abundance of coccids (Ortheziidae) was positively correlated with densities of ants. To gain a better understanding of the position of spiders, ants and other dominant invertebrate groups in the studied food web and important trophic links, we used a stable isotope analysis ((15)N and (13)C). Adult wandering spiders were more enriched in (15)N relative to (14)N than juveniles, indicating a shift to predatory prey groups. Juvenile wandering and web-building spiders showed delta(15)N ratios just one trophic level above those of Collembola, and they had similar delta(13)C values, indicating that Collembola are an important prey group for ground living spiders. The effects of spiders demonstrated in the field experiment support this result. We conclude that the food resource of spiders in our study system is largely based on the detrital food web and that their effects on herbivores are weak. The effects of ants are not clear-cut and include predation as well as mutualism with herbivores. Within this diverse predator guild, intraguild interactions are important structuring forces.

Animals↗

PubMed1997

Spider phobia in children: disgust and fear before and after treatment.

Fear of spiders, disgust sensitivity, and spiders' disgust-evoking status were assessed in a group of spider phobic girls (n = 22) who applied for treatment, in a group of non-phobic girls (n = 21), and in the parents of both groups of children. The phobic girls were tested both before and after behavioural treatment which consisted of 1.5 hr eye movement desensitization and reprocessing and 1.5 hr exposure in vivo. Findings support the idea that disgust is an important aspect of spider phobia: (a) spider phobic girls exhibited higher levels of disgust sensitivity and considered spiders per se as more disgusting than non-phobic girls; (b) there was a parallel decline of spider fear and spiders' disgust-evoking status as a result of treatment; and (c) spiders' disgust-evoking status was relatively strong in mothers of spider phobic girls. The latter finding may indicate, that the acquisition of spider fear is facilitated by specific parental disgust reactions when confronted with spiders.

Adolescent↗

PubMed2004

Predation by cosmopolitan spiders upon the medically significant pest species Loxosceles reclusa (Araneae: Sicariidae): limited possibilities for biological control.

Interspecific predation of three cosmopolitan house spiders, Achearanea tepidariorum (Kock 1841) (Theridiidae), Steotoda triangulosa (Walckenaer 1802) (Theridiidae), and Pholcus phalangioides (Doleschall 1859) (Pholcidae), and the medically significant brown recluse spider, Loxosceles reclusa (Sicariidae) were examined to evaluate transitive predatory relationships and to explore the potential use of cosmopolitan spiders as effective biological control agents on L. reclusa. Fifty houses from northeastern Kansas were visually inspected from May to December 2002 for cosmopolitan spiders and L. reclusa. In 25 houses, insect monitoring traps were used to sample spider diversity and abundance. The remaining 25 houses were monitored to examine intraguild predation and spider behavior. If cosmopolitan spiders have the ability to regulate or decrease L. reclusa populations, houses with large cosmopolitan spider populations are expected to have significantly fewer L. reclusa than houses without cosmopolitan spiders. Predation and/or evidence of predation by all three cosmopolitan spiders on L. reclusa was detected in 68% of houses. Spearman's rank correlation analysis showed overall positive relationships between population densities of cosmopolitan spiders and L. reclusa. When evaluated independently, the presence of both A. tepidariorum and S. triangulosa showed negative, yet nonsignificant, relationships with L. reclusa densities, whereas P. phalangioides showed a positive nonsignificant relationship. Although statistical tests showed a decrease in L. reclusa population densities with increased population densities of two cosmopolitan species, alluding to a potential beneficial interaction for biological control, observations of spider behavior, web positioning (niche partitioning), and predation showed little possibility of biological control capabilities.

Animals↗

PubMed2004

Beat sampling accuracy in estimating spruce spider mite (Acari: Tetranychidae) populations and injury on juniper.

The use of a standardized beat sampling method for estimating spruce spider mite, Oligonychus ununguis (Jacobi) (Acari: Tetranychidae), densities on a widely used evergreen ornamental plant species, Juniperus chinensis variety 'Sargentii' A. Henry (Cupressaceae), was examined. There was a significant positive relationship between total spruce spider mite densities and spider mite densities from beat sampling on juniper. The slope and intercept of the relationship may be used by pest managers to predict total spider mite densities on plants from beat sample counts. Beat sampling dramatically underestimates the total number of spider mites on a foliage sample. The relationships between spruce spider mite feeding injury and spider mite density estimates from beat sampling juniper foliage and total spider mite counts on foliage were also examined. There was a significant positive relationship between spruce spider mite density as estimated from beat sampling and injury to the plants. There was a similar positive relationship between the total number of spruce spider mites and injury to the plants, suggesting that a pest manager could use beat sampling counts to estimate plant injury and related thresholds. These findings have important implications to decision-making for spruce spider mite control, especially as it relates to threshold levels and determining rates of predator releases. Further assessment of the effectiveness of beat and other sampling methods across multiple spider mite- host plant associations needs to be examined to enable pest managers to select sampling plans that are feasible and reliable.

Animals↗

PubMed1995

Regulatory responses of the coxal organs and the anal excretory system to dehydration and feeding in the spider Porrhothele antipodiana (Mygalomorpha: Dipluridae)

The roles of coxal and anal excretion in the regulation of haemolymph osmolality, [Na+] and [K+] were studied in the mygalomorph spider Porrhothele antipodiana (mass 0.71.0 g) under differing conditions of feeding and hydration state. Dehydration of starved spiders by removal of drinking water caused progressive mass loss at a rate of about 2.5 % of initial body mass per day and was associated with increases in the whole-body [Na+] and [K+] and in the osmolality, [Na+] and [K+] of the haemolymph. On provision of prey, feeding partially restored this mass loss but further elevated body and haemolymph ion concentrations. Dehydration reduced fluid excretion by the anal excretory system and the four coxal organs in both starved and feeding spiders. Starved hydrated spiders initially produced anal urine at 5 µl day-1 and this was progressively reduced to zero after 4 days of water deprivation. Spiders dehydrated to less than 12 % mass loss would nevertheless feed and this initiated a small post-prandial anal diuresis (<5 µl day-1 compared with >30 µl day-1 in fed hydrated spiders). Coxal fluid was produced by dehydrated spiders only during feeding and was delivered into the prey, the rate of production by single organs decreasing from about 19 µl h-1 g-1 body mass in hydrated spiders to about 4 µl h-1 g-1 body mass in spiders dehydrated to 11 % mass loss. There was an increase in urine [K+] and in the rate of anal K+ excretion associated with ad libitum feeding in dehydrated spiders. However, urine [Na+] and the rate of anal excretion of Na+ were not increased by feeding. This was associated with an increase in [K+] of the stercoral fluid above that observed in either fed or starved hydrated spiders, but no significant change in [Na+]. Conversely, [Na+] of the coxal fluid produced during feeding was increased by dehydration whereas [K+] was not. These observations are consistent with the previously postulated roles of the coxal organs (Na+) and anal system (K+) in the excretion of ions ingested with the prey. Full elimination of the prey ions was accomplished only after drinking water was resupplied, which initiated further anal and coxal diureses. Smaller anal and coxal diureses also occurred on rehydration of unfed spiders. The production of coxal fluid in the absence of prey is further evidence that the coxal organs have a true excretory function besides, presumably, assisting ingestion. During dehydration and feeding, P. antipodiana, unlike many insects, is unable simultaneously to conserve water and to eliminate ions by production of a highly concentrated excretory fluid. Both coxal fluid and anal urine were approximately iso-osmotic to the haemolymph and the urine was markedly hypo-ionic.

Journal Article↗

PubMedDate not supplied

Spider bites.

BACKGROUND: This review provides the physician with a clinical approach to the diagnosis and management of spider bites. It examines the recent literature concerning management of bites causing dermonecrosis, secondary infection, neuromuscular damage, and allergic reactions. METHODS: Using the key words "spider bites," "brown recluse spider bites," "necrotic arachnidism," "black widow spider bites," "latrodectism," and "Tegenaria agrestis (Hobo spider)," the MEDLINE files were researched for articles pertinent to the practicing physician. Texts related to spiders and spider bites were also consulted. RESULTS AND CONCLUSIONS: At least 60 species of spiders have been implicated in human bites. Most cause bites of minimal medical importance, requiring little treatment. Some (brown recluse, Hobo spider) cause severe cutaneous and systemic reactions requiring intensive medical management. The black widow bite can cause severe neurologic problems requiring the use of antivenin. Spider bites are frequently difficult to diagnose because the spider is not seen at the time of the suspected bite. Such bites should be labeled arthropod bites, vector unknown.

Anti-Infective Agents↗

PubMed2006

The significance of cutaneous spider naevi in children.

BACKGROUND: Cutaneous spider naevi are commonly considered to be a clinical sign of chronic liver disease. Little is known about their occurrence in children. AIM: To evaluate the occurrence of spider naevi in children with and without liver disease. METHODS: The presence of spider naevi was investigated in 460 children, 34 of whom had chronic liver disease. RESULTS: Of children without liver involvement, 38% had at least one spider naevus. The prevalence of spider naevi increased with age. Of control patients aged 5 to 15 years, 2.5% had more than five spiders present. Although eight of 10 children with cirrhosis had at least one spider naevus, only four of 34 children with chronic liver disease had five or more spiders present. Most spiders were on the hands and very few were >5 mm in size. CONCLUSIONS: Children with liver disease rarely have large numbers of spider naevi. Although the finding of five or more spider naevi is more common in liver disease, many normal children also have one or more of these lesions.

Adolescent↗

PubMed2004

Prospective cohort study of definite spider bites in Australian children.

OBJECTIVES: To describe the clinical effects of spider bites in a paediatric population and compare to bites in an adult population. METHODS: Prospective follow up study of children with definite spider bites where the spiders were immediately collected and expertly identified. Cases were recruited from Australian emergency departments and poison information centres and followed up. Data were collected on circumstances of bites and clinical effects, and compared with similar data from adult spider bites. RESULTS: There were 163 cases (62% male, 38% female; age <16, median age 7 years, interquartile range (IQR): 3-11 years). The median duration of effects was 2 h (IQR 0.25-12 h). The commonest spiders were Huntsman spiders (Sparassidae) and Orb weavers (Araneidae), and comparatively few bites by theridiid spiders, including Red-back spiders. Pain or discomfort occurred in all bites and was severe in 20%. Local effects included puncture marks/bleeding (36%) and red mark/redness (73%). Systemic effects occurred in only 6% of cases. There were no necrotic lesions or ulcers as a consequence of any spider bites (0%; 97.5% CI 0.0-2.2%) and no early allergic reactions or secondary infections. The median duration of clinical effects was shorter than adults, the frequency of severe pain was less than adults and systemic effects were less common in children. CONCLUSIONS: Paediatric spider bite causes minor effects in the majority of cases, and is unlikely to cause necrotic ulcers, allergic reactions or infection. The severity and duration of effects differ from adults.

Adolescent↗

PubMed2006

Evaluative learning and emotional responding to fearful and disgusting stimuli in spider phobia.

The present study explores possible changes between spider phobics (N=22) and nonphobics (N=28) in fear, disgust, and neutral ratings of neutral expressions as a result of their pairing with spiders. No statistically significant differences were detected between pre and post fear ratings of the expressions as a result of their association with spiders. However, post disgust ratings were marginally higher than pre disgust ratings and post neutral ratings were significantly lower than pre neutral ratings. The present study also examined differences in fear and disgust responding to threat-relevant and disgust-relevant stimuli between spider phobics and nonphobics. Spider phobics reported significantly more fear and disgust than nonphobics towards threat and disgust-relevant stimuli. The relation between spider phobia and disgust responding to spiders was partially mediated by fear whereas the relation between spider phobia and disgust responding to rotting foods and body products was fully mediated by fear. Emotional responding to threat-relevant and disgust-relevant stimuli was also significantly associated with disgust sensitivity when controlling for trait anxiety. These findings support the notion that the disgust response in spider phobia is independent of fear to the extent that it is specifically bound to spiders.

Adolescent↗

PubMedDate not supplied

Is the mechanical strength of spider's drag-lines reasonable as lifeline?

Drag-lines play a role as a lifeline for a spider to move and fall from trees. The mechanical strength of the drag-lines may be related to the spider's weight since spiders hang from them. The safety coefficient of drag-lines as the lifeline should be considered for the mechanical strength of the drag-lines consisting of double filaments. It was found that the elastic limit strength and breaking strength increase linearly with spider's weight, about twice the spider's weight corresponds to the elastic limit strength, and about six times the spider's weight corresponds to the breaking strength of drag-lines. In other words, the spider's weight corresponds to the elastic limit strength for the single filament. This means that a spider can act safely by one filament even though another filament is broken down. It should be an outcome from spider's long history of 400-million-years evolution. These findings may give a maximal efficiency for the mechanical strength of spider's drag-lines.

Animals↗

PubMed2005

The functions of societies and the evolution of group living: spider societies as a test case.

Many models have been advanced to suggest how different expressions of sociality have evolved and are maintained. However these models ignore the function of groups for the particular species in question. Here we present a new perspective on sociality where the function of the group takes a central role. We argue that sociality may have primarily a reproductive, protective, or foraging function, depending on whether it enhances the reproductive, protective or foraging aspect of the animal's life (sociality may serve a mixture of these functions). Different functions can potentially cause the development of the same social behaviour. By identifying which function influences a particular social behaviour we can determine how that social behaviour will change with changing conditions, and which models are most pertinent. To test our approach we examined spider sociality, which has often been seen as the poor cousin to insect sociality. By using our approach we found that the group characteristics of eusocial insects is largely governed by the reproductive function of their groups, while the group characteristics of social spiders is largely governed by the foraging function of the group. This means that models relevant to insects may not be relevant to spiders. It also explains why eusocial insects have developed a strict caste system while spider societies are more egalitarian. We also used our approach to explain the differences between different types of spider groups. For example, differences in the characteristics of colonial and kleptoparasitic groups can be explained by differences in foraging methods, while differences between colonial and cooperative spiders can be explained by the role of the reproductive function in the formation of cooperative spider groups. Although the interactions within cooperative spider colonies are largely those of a foraging society, demographic traits and colony dynamics are strongly influenced by the reproductive function. We argue that functional explanations help to understand the social structure of spider groups and therefore the evolutionary potential for speciation in social spiders.

Animals↗

PubMed2001

Signal polymorphism in the web-decorating spider Argiope argentata is correlated with reduced survivorship and the presence of stingless bees, its primary prey.

Many spiders, and in particular those in the genus Argiope, spin highly visible web decorations whose function and significance are the subject of spirited debate. In this work, we present data to address two of the competing hypotheses that fuel this controversy. In particular, we examine the relationship between the presence of web decorations and spider survivorship (predator-protection hypothesis) and the relationship between the presence of prey and spider decorating behavior (the prey-attraction hypothesis). Our laboratory studies reveal that the decorating behavior of the spider A. argentata has a genetic component but that the expression of decorating behavior tends to be elicited only when a spider is well fed. Furthermore, our field studies show that in the presence of abundant stingless bees, spider decorating behavior is induced. Nevertheless, our field surveys also suggest that spiders that decorate their webs show reduced survivorship. We propose that the high correlation between web decorating in the presence of stingless bees supports the hypothesis that A. argentata engage in decorating behavior when attracting or targeting specific prey types. However, we also propose that web decorations attract the predators of A. argentata because high-frequency decorators suffer lower survivorship than spiders that decorate moderately or rarely. These findings suggest that spider web decorating behavior is affected by conflicting selection pressures: the positive effect of prey attraction versus the negative effect of predator attraction. Due to the heritable component of decorating behavior, web decorating among A. argentata is likely to be particularly sensitive to the spider's local ecology as well as local patterns of gene flow.

Animals↗

PubMed2003

Trichobothrial mediation of an aquatic escape response: directional jumps by the fishing spider, Dolomedes triton, foil frog attacks.

Fishing spiders (Pisauridae) frequent the surfaces of ponds and streams and thereby expose themselves to predation by a variety of aquatic and semi-aquatic vertebrates. To assess the possibility that the impressive jumps of fishing spiders from the water surface function in evading attacks by frogs, attacks by bullfrogs (Rana catesbiana) and green frogs (R. clamitans) on Dolomedes triton were studied. Both the attack dynamics of the frogs and the evasive behaviors of the spiders were recorded at 250 frames per second. A freeze-dried bullfrog, propelled toward spiders with acceleration, posture, and position that approximated the natural attack posture and dynamics, was used to assess the spiders' behavior. Qualitatively, the spiders responded to these mock-attacks just as they had to attacks by live frogs: jumping (N=29 jumps, 56.9% of instances), rearing the legs nearest the attacking frog (N=15, 29.4%), or showing no visible response (N=7, 13.7%). Spiders that jumped always did so away (in the vertical plane) from the attack (mean =137 degrees vs. vertical at 90 degrees or horizontally toward the frog at 0 degrees ). The involvement of the trichobothria (leg hairs sensitive to air movements), and the eyes as sensory mediators of the evasion response was assessed. Spiders with deactivated trichobothria were significantly impaired relative to intact and sham-deactivated spiders, and relative to spiders in total darkness. Thus, functional trichobothria, unlike the eyes, are both necessary and sufficient mediators of the evasion response. Measurements of air flow during frog attacks suggest that an exponential rise in flow velocity is the airborne signature of an attack.

Animals↗

PubMed1999

Leg autotomy in a spider has minimal costs in competitive ability and development.

A number of species have the ability to autotomize limbs voluntarily, but animals that have lost limbs often face substantial costs. We examined the frequency of leg loss and its effects on competitive ability and development in the spider Holocnemus pluchei (Araneae: Pholcidae), a family of spiders known for its readiness to autotomize legs. Leg loss was common in field populations, with 7.5% of all surveyed spiders missing at least one leg, most commonly one of the anterior pair. More spiders were missing multiple legs than expected by chance, suggesting that leg loss events are not independent. Large adult spiders were missing legs more frequently than were small spiders. The competitive ability of injured males was tested in three contexts. In the field, no effect of leg loss was found on the ability of spiders to remain in webs into which they were introduced. In the laboratory, no effect of leg loss was found on the ability to fight with a single opponent over a prey, except that injured spiders were more likely to lose high-intensity fights. There was no difference between intact and injured males in their ability to compete with three females for limited prey. Leg loss significantly affected development time. The moult interval during the instar in which the injury occurred increased by approximately 15%. However, the growth rate for injured spiders was slightly but not significantly faster in the instar following leg loss, and total development time of the two instars together did not differ significantly between treatments. No spider showed any signs of regeneration. We conclude that, although there were some statistically significant differences between intact and injured males, these are unlikely to have major impacts on fitness, in contrast to findings in other species. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1999

Feeding experience affects web relocation and investment in web threads in an orb-web spider, Cyclosa argenteoalba.

Orb-web spiders often relocate their webs when they assess a web site as prey poor. When a spider spins its web at a new site, it may not be able to assess the prey availability at the site accurately on the first day, owing to stochastic variation in foraging success, but it is gradually able to make an assessment. Therefore, a spider's foraging behaviour may change according to how long it has been at its current web site. To test this possibility, we conducted a prey removal experiment, with the spider Cyclosa argenteoalba, to compare the response to prey deprivation of spiders that were on new sites with that of spiders that had been at a site for several days. Spiders in both groups had a higher relocation rate than the natural rate, but more spiders in the new-site group relocated their webs. Spiders thus seemed to use previous experience of prey capture at a web site to decide whether to relocate their web. The total length of silk thread in a web was greater on the second day at a new web site than on the first. We suggest that spiders minimize their investment in web threads until they are certain that the web site is prey rich. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed2000

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.

Journal Article↗

PubMed2004

White-tailed spider bites--arachnophobic fallout?

AIM: To investigate if public concern regarding the toxic effects of the bites from white-tailed spiders, Lampona cylindrata and L. murina, is reflected in the case histories of patients admitted to Christchurch Hospital with a diagnosis of spider bite. METHODS: The case histories of patients admitted to Christchurch Hospital with a diagnosis of 'contact with venomous spiders' were examined for evidence that the patients developed necrotising arachnidism. RESULTS: Ten patients were admitted to Christchurch Hospital between January 2001 and January 2003 with a diagnosis of 'contact with venomous spiders'. We found no evidence that patients developed necrotising arachnidism. No patients admitted to Christchurch Hospital required re-admission to treat sequelae of the putative spider bite. Support for a spider bite as the causative agent was not robust and alternative agents could have been the cause. CONCLUSIONS: The public's fear of bites from white-tailed spiders is likely misplaced and, if the spider was not caught in the act of biting the patient, alternative diagnoses should be considered before assuming a white-tailed spider was responsible for the patient's symptoms.

Animals↗