Silk elasticity as a potential constraint on spider body size

Silk is known for its strength and extensibility and has played a key role in the radiation of spiders. Individual spiders use different glands to produce silk types with unique sets of proteins. Most research has studied the properties of major ampullate and capture spiral silks and their ecological implications, while little is known about minor ampullate silk, the type used by those spider species studied to date for bridging displacements. A biomechanical model parameterised with available data shows that the minimum radius of silk filaments required for efficient bridging grows with the square root of the spider’s body mass, faster than the radius of minor ampullate silk filaments actually produced by spiders. Because the morphology of spiders adapted to walking along or under silk threads is ill suited for moving on a solid surface, for these species there is a negative relationship between body mass and displacement ability. As it stands, the model suggests that spiders that use silk for their displacements are prevented from attaining a large body size if they must track their resources in space. In particular, silk elasticity would favour sexual size dimorphism because males that must use bridging lines to search for females cannot grow large.     

Offspring recognition by mother crab spiders with extreme maternal care

Maternal care is provided by several spider species, but there are no reports of mother spiders recognizing their young, which suggests that maternal care can be exploited by unrelated individuals. Diaea ergandros, a crab spider with extreme, sacrificial maternal care, does accept unrelated spiderlings (ca. 43.9% of spiderlings) into its nest in areas of high nest density. However, a field and a laboratory experiment with mother spiders and natural and adoptive spiderlings demonstrated that mothers did recognize their own offspring. Recognition was not expressed in survival as adopted (unrelated) spiderlings had similar survival rate to that of natural offspring. Instead it was displayed in growth; mother D. ergandros caught large prey items for their own offspring, but not for adopted spiderlings, and so natural offspring grew more than adopted spiderlings. Also, mothers produced trophic oocytes, which are important for the sacrificial care that influences spiderling survival, only when they lived with their own offspring.     

Haltung und Zucht der Geißelspinne (Damon variegatus) (Phrynichidae) (Chelicerata: Amblypygi)

In the temporary carboniferous hall of „GONDWANA – Das Prähistorium“ in Germany, whip spiders (Damon variegatus) were kept and bred. 3,3 were purchased from a dealer in summer 2007. The night active spiders were kept together in a terrarium. No aggresions were observed. The animals were fed little locusts, young hissing cockroaches, and crickets. In 2008 courtship display and mating could be observed. The biggest male was the only active one. After 7 days after the intake of the spermatophores all females carried eggsacs under the ophistosoma. Each egg sack contained approximately 25–30 eggs. During the carrying phase only one female feasted on a cricket. 98 days after the egg sack was produced the young spiderlings hatched. The coloration of the spiderlings was completely different from the coloration of the adults. The spiderlings were carried by the female for the next 9 days. Then, the spiderlings moulted and left the female immediately. The adults were now separated from their young. The three groups of spiderlings stayed together in a smaller terrarium. However, each group from each female stayed separate from the others for weeks. The second moulting took place 41 days after the first one. No cannibalism was observed. Obviously Damon variegatus seems to be a spider with a social touch. If the terrarium and the climate conditions inside are adapted to the needs of the whip spiders keeping and breeding is possible. The species is highly attractive to visitors.     

A mass rearing method for the linyphiid spider species Erigone atra (Blackwall) (Araneae: Linyphiidae)

Abstract:  A mass rearing method for Erigone atra (Blackwall) (Araneae: Linyphiidae) allowing continuous laboratory rearing is described. Twenty 1–2-day old spiderlings were kept together in plastic boxes, which were filled with soil containing a culture of the Collembola species, Lepidocyrtus lanuginosus (Gmelin) (Entomobryidae), and serving the spiders as a continuous available prey source. Once per week vestigial-wing fruit flies of Drosophila melanogaster Meigen (Diptera: Drosophilidae) were provided as additional prey. In addition, the rearing boxes were filled with wood-wool serving spiders as points of contact for their webs. After 3–5 weeks most of the spiderlings developed to adults, which were separated individually into glass tubes filled with soil and Collembola until all of them became adult. To produce a new generation of spiders 20–40 adult/subadult spiders originating from different mass rearing boxes were brought together and kept and fed in the same way as the spiderlings. Within a few days females started to produce eggsacs. The eggsacs were transferred into glass tubes filled with a layer of moist plaster of Paris until the spiderlings hatched, which were then bred as described above. Erigone atra was bred over 12 generations within a period of 2 years. The mean rearing success (from 1 to 2-day-old spiderlings to adults) was 59.3%. Decreasing rearing success, decrease of fecundity or decrease of adult spider size were not observed. Advantages and use of the mass rearing method are discussed in relation to rearing methods for other spiders.     

Haltung und Zucht der Geißelspinne (Damon variegatus) (Phrynichidae) (Chelicerata: Amblypygi)

In the temporary carboniferous hall of „GONDWANA - Das Prähistorium“ in Germany, whip spiders (Damon variegatus) were kept and bred. 3,3 were purchased from a dealer in summer 2007. The night active spiders were kept together in a terrarium. No aggresions were observed. The animals were fed little locusts, young hissing cockroaches, and crickets. In 2008 courtship display and mating could be observed. The biggest male was the only active one. After 7 days after the intake of the spermatophores all females carried eggsacs under the ophistosoma. Each egg sack contained approximately 25-30 eggs. During the carrying phase only one female feasted on a cricket. 98 days after the egg sack was produced the young spiderlings hatched. The coloration of the spiderlings was completely different from the coloration of the adults. The spiderlings were carried by the female for the next 9 days. Then, the spiderlings moulted and left the female immediately. The adults were now separated from their young. The three groups of spiderlings stayed together in a smaller terrarium. However, each group from each female stayed separate from the others for weeks. The second moulting took place 41 days after the first one. No cannibalism was observed. Obviously Damon variegatus seems to be a spider with a social touch. If the terrarium and the climate conditions inside are adapted to the needs of the whip spiders keeping and breeding is possible. The species is highly attractive to visitors.     

Tracing the evolutionary origin of a visual signal: the coincidence of wrap attack and web decorating behaviours in orb web spiders (Araneidae)

The silk decorations that adorn the webs of many orb-web spiders are thought to have a signal function, but the evolution of the decorating behaviour remains unresolved. The decoration signal is maintained apparently because it improves foraging efficiency, through either increased encounter rates with prey or reduced damage to the web. Recent investigations suggest that the decorations may originate in a regulation of the activity of the aciniform silk glands, which produce silk for both decorating the web and wrapping prey. This view predicts a link between decorating behaviour and a preference for restraining prey by wrapping with silk, which is evident among species of Argiope spiders. Here I compare the frequency of the wrap attack behaviour in four species of orb-web spiders that occupy the same habitat, but differ in their silk decorating behaviour: two species, Plebs bradleyi and Gea theridioides, build silk decorations, while the other two, Araneus hamiltoni and Backobourkia brounii do not. Spiders were presented with prey items that varied in the ease with which they could be captured, with houseflies being more easily subdued than house crickets. As predicted, the silk decorating species used wrap attacks significantly more often than non-decorating spiders, irrespective of the prey species. These data support the view that both behaviours are evolutionary linked. I propose that silk decorating originated from the evolution of wrap attacking, and that silken web decorations have later evolved into a signal and are now maintained for that function.     

Spider silk reduces insect herbivory

The role of predators in food webs extends beyond their ability to kill and consume prey. Such trait-mediated effects occur when signals of the predator influence the behaviour of other animals. Because all spiders are silk-producing carnivores, we hypothesized that silk alone would signal other arthropods and enhance non-lethal effects of spiders. We quantified the herbivory inflicted by two beetle species on green bean plants (Phaseolus vulgaris) in the presence of silkworm silk and spider silk along with no silk controls. Single leaflets were treated and enclosed with herbivores in the laboratory and field. Another set of leaflets were treated and left to experience natural herbivory in the field. Entire plants in the field were treated with silk and enclosed with herbivores or left exposed to herbivory. In all cases, the lowest levels of herbivory occurred with spider silk treatments and, in general, silkworm silk produced intermediate levels of leaf damage. These results suggest that silk may be a mechanism for the trait-mediated impacts of spiders and that it might contribute to integrated pest management programmes.     

Costs and benefits of facultative aggregating behaviour in the orb-spinning spider Gasteracantha minax Thorell (Araneae: Araneidae)

Abstract The potential costs and benefits of foraging in aggregations are examined for the orb-spinning spider Gasteracantha minax. Web-site tenacity is low in this species; individuals frequently move among sites, thereby joining aggregations of different sizes. Female spiders in aggregations suffered lower predation rates and attracted more males than their solitary counterparts. However, aggregated eggsacs, probably produced by females in aggregations, experienced higher rates of parasitism than solitary eggsacs. We found no evidence of higher prey capture success rates among spiders in aggregations. However, we demonstrate a novel way in which spiders can increase their foraging efficiency by decreasing silk investment. A spider spinning a web within an existing aggregation can attach the support threads of its web to those of other webs, thereby exploiting the silk produced by other spiders.     

The allometry of CNS size and consequences of miniaturization in orb-weaving and cleptoparasitic spiders

Allometric studies of the gross neuroanatomy of adults from nine species of spiders from six web-weaving families (Orbicularia), and nymphs from six of these species, show that very small spiders resemble other small animals in having disproportionately larger central nervous systems (CNSs) relative to body mass when compared with large-bodied forms. Small spiderlings and minute adult spiders have similar relative CNS volumes. The relatively large CNS of a very small spider occupies up to 78% of the cephalothorax volume. The CNSs of very small spiders extend into their coxae, occupying as much as 26% of the profile area of the coxae of an Anapisona simoni spiderling (body mass < 0.005 mg). Such modifications occur both in species with minute adults, and in tiny spiderlings of species with large-bodied adults. In at least one such species, Leucauge mariana, the CNS of the spiderling extends into a prominent ventral bulge of the sternum. Tiny spiders also have reduced neuronal cell body diameters. The adults of nearly all orbicularian spiders weave prey capture webs, as do the spiderlings, beginning with second instar nymphs. Comparable allometric relations occur in adults of both orb-weaving and cleptoparasitic species, indicating that this behavioral difference is not reflected in differences in gross CNS allometry.     

State-dependent decisions in nest site selection by a web-building spider

Foraging decisions may reflect a trade-off between food intake and safety and can also be influenced by the animal's internal state. Foraging in the web-building spider Stegodyphus lineatus depends on a capture web associated with a retreat (the nest). The relocation of nests, including the take-over of conspecific nests, may be viewed as a foraing decision, which depends on risk of exposure, cost of silk production and hunger state. We investigated a possible state-dependent trade-off in nest site choice of S. lineatus spiderlings. The philopatric nature ofS. lineatus implies a high risk of encounters with potentially cannibalistic conspecifics and a potential loss of inclusive fitness because encountered conspecifics are likely to be kin. To test for state dependence of foraging decisions, we compared preferences of well-fed and hungry spiders for their own nests and those of siblings and nonsiblings. We expected satiated spiders to prefer their own to conspecific nests and hungry spiders to choose the risky option of a conspecific nest. SinceS. lineatus is less aggressive towards kin, we tested the ability of spiders to discriminate kin by silk-bound cues. Because of this reduced aggression, preference for kin nests should be safer than preference for nonkin nests. A strong preference for self-nests demonstrated self-recognition in well-fed spiders. However, neither well-fed nor hungry spiders discriminated between nests of siblings and nonsiblings. Well-fed spiders preferred self-nests to empty chambers, but showed no discrimination between nonself-nests and empty chambers. Hungry spiders showed a reduced preference for self-nests, suggesting that hunger elicits a more risky foraging strategy. A tendency of hungry spiders to adopt the nests of conspecific spiders may reflect a silk-saving strategy. We conclude that S. lineatus spiders show state-dependent decision making in nest site selection. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Juvenile bolas spiders attract psychodid flies

Large immature and mature female bolas spiders of the genus Mastophora attract certain male moths by aggressive chemical mimicry of those moth species' sex pheromones. These older spiders capture moths by swinging a bolas (i.e., a sticky globule suspended on a thread) at the approaching male moths. Juvenile bolas spiders do not use a bolas, but instead use their first two pairs of legs to grab prey, which our field observations suggested were primarily nematocerous Diptera. Our field experiments over a 2-year period demonstrated that juvenile bolas spiders attract moth flies (Psychodidae), with each species apparently specializing on a particular prey species. In three experiments, sticky traps containing young Mastophora phrynosoma spiderlings consistently captured significantly more male Psychoda phalaenoides than were captured on traps containing spiderlings of other Mastophora species or no spiderlings (control traps). Results from two of the three experiments suggested that Mastophora hutchinsoni spiderlings attract male Psychoda trinodulosa. Only two of our experiments included Mastophora bisaccata and those produced contrasting results. In the first experiment, M. bisaccata appeared to attract P. phalaenoides, albeit in lower numbers than were captured on traps containing M. phrynosoma. However, in a second experiment the following year, M. bisaccata spiderlings attracted Psychoda satchelli, a species that had not been caught on any traps the previous year. As suggested by a systematist four decades ago, the taxon currently called M. bisaccata may consist of two or more sibling species, which could account for the contrasting results obtained from our two experiments involving M. bisaccata. This is the first reported evidence that, during early developmental stadia before these spiders attract moths, juvenile bolas spiders attract their prey.     

Interactions among young stages of the wolf spiders Pardosamoesta and P. mackenziana (Araneae: Lycosidae)

Young stages of the wolf spiders Pardosa moesta and P . mackenziana coexist on the forest floor in a deciduous forest in central Alberta, yet nothing is known of the potential interactions between and among these ubiquitous species. An experiment, using a series of 0.25-m² arenas, was designed to test for inter- and intraspecific exploitative competition. Experimental treatments were established in the arenas in late July. Treatments involved stocking recently hatched spiderlings of each species alone, and with both species together at natural (10 spiderlings per arena) and two times the natural densities. In September the arenas were searched for Pardosa spiderlings, and the survival and mass gain of each species were determined. Other predatory arthropods, and Collembola, a common prey of young wolf spiders, were counted in the arenas before the experimental treatments were established and at the end of the experiment. No evidence for competitive interactions was uncovered, but spiderling survival was 29% for P . moesta and 20% for P . mackenziana , suggesting other mortality factors (e.g., cannibalism, intraguild predation) may be important. Top-down effects (predatory arthropods) had no effect on Pardosa survival. Bottom-up effects, however, were significant as treatments containing spiderlings had fewer Collembola compared to control arenas, further supporting the importance of spiders in leaf-litter food webs.     

The aggregating behaviour of <Emphasis Type="Italic">Argiope radon</Emphasis>, with special reference to web decorations

The existence of aggregations in taxa that are normally solitary poses questions regarding the costs and benefits of group living. Most orb-web spiders are solitary and are aggressive to conspecifics, but a few species aggregate in large numbers. These spiders benefit by enhancing the prey interception potential, but also suffer costs of increased predation and parasitism. In this study, we report on the natural history characteristics of the orb-web spider, Argiope radon, which not only lives in aggregations but also builds silk decorations. Our results show that A. radon aggregates facultatively and that the main benefit of aggregation that we could identify is enhanced mating potential. We also show that decorations built by A. radon are highly visible to both model prey and predator, and suggest that solitary individuals with longer and more frequent decorations may offset the foraging advantage of being in aggregations.     

真水狼蛛幼蛛各龄期的形态特征和生长发育

幼蛛在蜘蛛的种群中占有很大比例。通过室内饲养。获得了不同龄期的真水狼蛛幼蛛。其体重、体长、背甲宽、步足长、眼域宽以及中斑下的条形纵斑长度都随着龄期的增大而增加。背甲宽和中斑下的条形斑纹长度可用来判断真水幼蛛的龄期。雌蛛的取食量大于雄蛛,高龄幼蛛大于低龄幼蛛。幼蛛在蜕皮时不取食,蜕皮后,取食量明显增加。     

Exploratory recruitment plasticity in a social spider (Anelosimus eximius)

Exploratory recruitment was investigated in an artificial experimental set-up on location in French Guyana. Groups of 200 freshly collected spiders of the neotropical social theridiid Anelosimus eximius were released on an open circular surface and offered a choice between two accessible shelters. Results indicated that a clear-cut collective decision was not always reached, unlike what we found using a different set-up in another set of experiments. Simulations were conducted using available information in order to explore the potential causes for this difference. Theoretical projections fit experimental data and strongly suggest that variability in the collective response results from a combination between modifications of the environment's properties and alteration of the recruitment procedure. Multiple variants of the theoretical set-up (including external bias) are investigated and emphasize plasticity in the collective response. New experimental studies are suggested and adaptative value of exploratory recruitment in social spiders is briefly discussed.     

The attraction of silk: base of group cohesion and collective behavior in social spiders

Social spiders differ from social insects by the production and the use of silk to build irregular webs. This silk prevents dispersion of the individuals and ensures the group cohesion during swarming and collective displacements, playing a part similar to tracks of pheromones in ants. A social spider Anelosimus eximius is attracted by conspecific silk and does not show any discrimination relative to its origin, excluding any group closure. The quantity of silk and the state of satiety of the individual modulate this attraction, and might explain how the spider society adapts the size of the web to its nutritional needs.     

Spiders spinning electrically charged nano-fibres

Most spider threads are on the micrometre and sub-micrometre scale. Yet, there are some spiders that spin true nano-scale fibres such as the cribellate orb spider, Uloborus plumipes. Here, we analyse the highly specialized capture silk-spinning system of this spider and compare it with the silk extrusion systems of the more standard spider dragline threads. The cribellar silk extrusion system consists of tiny, morphologically basic glands each terminating through exceptionally long and narrow ducts in uniquely shaped silk outlets. Depending on spider size, hundreds to thousands of these outlet spigots cover the cribellum, a phylogenetically ancient spinning plate. We present details on the unique functional design of the cribellate gland–duct–spigot system and discuss design requirements for its specialist fibrils. The spinning of fibres on the nano-scale seems to have been facilitated by the evolution of a highly specialist way of direct spinning, which differs from the aqua-melt silk extrusion set-up more typical for other spiders.     

Coordination of Behavioral Sequences Between Individuals During Prey Capture in a Social Spider, Anelosimus eximius

The analysis of collaborative predation sequences performed by groups of 10 individuals (females) in a nonterritorial permanent-social spider, A. eximius, shows that prey-captures are organized in successive steps. Spiders begin by throwing sticky silk, which hinders the prey in the web; they then throw dry silk, which completes the immobilization of the prey. The third step is characterized by bites that paralyze the prey that will be then carried. A concordance test reveals a coordination of the individual's acts that explains the collaborative prey-capture efficiency. No individual specialization in one type of act has been shown. On the contrary, by using living preys or artificially dead vibrated preys, we show that all individuals have equipotential behaviors. Furthermore, each spider is able to adjust its behavior to the state of the prey. Individuals already involved in prey transportation can again display bites or sticky silk throwing if the prey is artificially vibrated. This mechanism, which corresponds to stimergic processes responsible for self-organized phenomena, already described in social insects, permits a coordination of individual acts without the recourse of direct communication. These results permit us to understand better how individuals coordinate their acts and lead us to support the hypothesis that the transition between solitary species and social species in spiders could have been sudden.     

Drop and swing dispersal behavior of a tropical wandering spider: experiments and numerical model

Summary When exposed to certain air flows spiderlings of the wandering spider Cupiennius getazi (Ctenidae) drop from their dwelling plant and swing in the wind from a gradually lengthening dragline. If body contact is made with a nearby substrate the spiderling detaches. We refer to this form of aerial dispersal as the drop and swing dispersal behavior (DASDB). The dragline being only up to about 70 cm long and only rarely ruptured by the drag forces of the wind, this is a close range type of dispersal as opposed to the ballooning known for many other species of spiders. DASDB is readily elicited in spiderlings at an age of ca. 9 days (outside egg sac). At this age their mass is 1.26 ±0.35 mg and their yolk usually depleted. They then start to catch prey and escape from the unfavorable conditions in the small space around the egg sac where hundreds of spiderlings compete. Air flow rates effectively eliciting DASDB in the laboratory are between 0.2 m/s and 1.5 m/s. The number of spiderlings showing DASDB increases considerably if the air flow is turbulent as opposed to laminar. A numerical model defining the window within which DASDB is supported mechanically was developed from theoretical considerations. Taking the effective wind speeds and the mechanical properties of the dragline, the model accounts very well for the fact that actual rupture of the dragline was observed only rarely in C. Getazi. Other features of the DASDB are also correctly predicted. The model is not only applicable to DASDB but also to the drop and swing preballooning behavior known to occur in several other species of spiders.Abbreviations DASDB drop and swing dispersal behavior     

Side-effects of insecticides on two erigonid spider species

The current rearing technique forErigone atra (Blackwall) andOedothorax apicatus (Blackwall) (Araneae, Erigonidae) was improved. To reduce time spent rearing on live fruit flies the spiders were kept on a culture of the Collembola speciesLepidocyrtus lanuginosus (Gmelin) (Entomobryidae). Side-effects on spiders of two pyrethroid insecticides (fenvalerate and lambda-cyhalothrin) and one carbamate insecticide (pirimicarb) were tested. Sensitivity of adults of both sexes and juveniles to insecticides and their influence on the rate of emergence of spiderlings from cocoons were investigated using topical application, spraying or residual contact. LD₅₀ values for adults ranged from 0.49 to 2.52 ng a.i./spider for lambda-cyhalothrin and from 5.75 to 98.20 ng a.i./spider for fenvalerate. Topical application also resulted in up to a week's delay of web-building. A moving laboratory spraying equipment was used to spray spiders with different insecticide dosages and water volumes. Pyrethroids sprayed onto adults in webs had stronger effects than pyrethroids sprayed onto sitting or walking spiders on the soil surface. Residual contamination caused higher mortality of spiders after contact with lambda-cyhalothrin than fenvalerate. In all tests, males were more susceptible to pyrethroids than females; this difference was related to body weight. Mortality rate was higher forE. atra than forO. apicatus. Both pyrethroids were also toxic to spiderlings. Lambda-cyhalothrin inhibited emergence ofE. atra spiderlings from cocoons. Pirimicarb was harmless to both spider species.