Untangling the Tangle-Web: Web Construction Behavior of the Comb-Footed Spider Steatoda triangulosa and Comments on Phylogenetic Implications (Araneae: Theridiidae)

Theridiidae typically construct a three-dimensional web often described as irregular. The web consists of a supporting structure and lines under tension termed gumfooted lines. We used automated methods to observe web construction in the theridiid Steatoda triangulosa under laboratory conditions. Web construction lasted several nights. After orientation, spiders built a three-dimensional structure of several threads radiating sideways and downward from the retreat. To build gumfooted lines, they started from the retreat, moved along a structural thread, then dropped down to attach the thread to the lower substrate. On returning, they coated the lowest part of the thread with viscid silk before moving up along the same thread back to the structural thread. They then continued moving along the same structural thread to drop down again to build the next gumfooted line. This behavior was continued until the spiders had built a series of gumfooted lines (a bout). There were regular intervals between the construction of two bouts. Thus, a single web included many bouts built in different stages. We show that gumfooted lines are not homologues to sticky web elements of orb-weavers and present new synapomorphic characters that support the monophyly of Theridiidae + Nesticidae and the monophyly of araneoid sheet web weavers. Further, the time allocation pattern for different behavioral stages and the fine structure of a gumfooted line are presented.     

Wrap attack of the spider <Emphasis Type="Italic">Achaearanea tepidariorum</Emphasis> (Araneae: Theridiidae) by preying on mealybugs <Emphasis Type="Italic">Planococcus citri</Emphasis> (Homoptera: Pseudococcidae)

Predation by Achaearanea tepidariorum (Koch 1841) on mealybugs Planococcus citri (Risso 1813) is facilitated by the design of its web, which features a tangle of sticky gumfooted lines, and wrap attacks as well as the ability to handle the prey, whose body is covered with a waxy secretion, via silk. Crawling, i.e., wingless, mealybugs (in particular those in the nymphal stages and adult females and, to a lesser extent, winged males) are caught by means of the gumfooted lines, covered with globules of an adhesive secretion. The process of wrap attack and subsequent handling of the captured prey is a series of the following consecutive events: (1) confining and immobilising the mealybugs with sticky silk; (2) biting with chelicerae and paralyzing the prey with a toxin; (3) detaching the confined prey, attached to the tense threads, from the plant surface and catapulting it toward the central section of the web; (4) wrapping the catapulted prey in viscid silk emitted by the spinning apparatus; (5) transporting the wrapped prey to the central section of the web; (6) wrapping the prey in the central section of the web in nonsticky silk, whose tufts are present in this part of the web even before the attack; (7) filling the prey with digestive fluid; (8) sucking the prey empty; and (9) cleaning the chelicerae and mouth parts. The process of silk tuft wrapping was described for the first time. The described ability to hunt mealybugs implies the possibility of using A. tepidariorum spiders for biological control of these pests.     

Biomechanical variation of silk links spinning plasticity to spider web function

Spider silk is renowned for its high tensile strength, extensibility and toughness. However, the variability of these material properties has largely been ignored, especially at the intra-specific level. Yet, this variation could help us understand the function of spider webs. It may also point to the mechanisms used by spiders to control their silk production, which could be exploited to expand the potential range of applications for silk. In this study, we focus on variation of silk properties within different regions of cobwebs spun by the common house spider, Achaearanea tepidariorum. The cobweb is composed of supporting threads that function to maintain the web shape and hold spiders and prey, and of sticky gumfooted threads that adhere to insects during prey capture. Overall, structural properties, especially thread diameter, are more variable than intrinsic material properties, which may reflect past directional selection on certain silk performance. Supporting threads are thicker and able to bear higher loads, both before deforming permanently and before breaking, compared with sticky gumfooted threads. This may facilitate the function of supporting threads through sustained periods of time. In contrast, sticky gumfooted threads are more elastic, which may reduce the forces that prey apply to webs and allow them to contact multiple sticky capture threads. Therefore, our study suggests that spiders actively modify silk material properties during spinning in ways that enhance web function.     

Host behavior modification of Achaearanea tingo (Araneae: Theridiidae) induced by the parasitoid wasp Zatypota alborhombarta (Hymenoptera: Ichneumonidae)

Behavioral manipulation involving Zatypota (Ichneumonidae: Pimplinae) parasitoids and their spider hosts is usually associated with an increase in web complexity at the location where the parasitoid larva builds its cocoon. A higher number of web threads at this location may improve stability and provide a physical barrier against potential predators. However, we observed that parasitized individuals of Achaearanea tingo attacked by Z. alborhombarta change the three‐dimensional structure of their webs to a very simple and strong structure composed of two cables attached to the surrounding vegetation. This structure holds the curled leaf formerly used by the spider as a shelter. The parasitoid larva remains protected within this shelter after killing the host. The architectural pattern of the cocoon webs of A. tingo indicates that host manipulation is characterized by the repetition of one specific subroutine involved in web construction. Similar alterations have been previously described for cocoon webs constructed by parasitized orb‐weavers, but not for the three‐dimensional webs of theridiids.     

THE WEB-SPINNING PROCESS AND WEB-STRUCTURE OF LATRODECTUS TREDECIMGUTTATUS, L. PALLIDUS AND L. REVIVENSIS

The web structure and the web spinning process of Latrodectus tredecimguttatus Rossi, Latrodectus pallidus Cambridge and Latrodectus revivensis Shulov have been investigated, particular attention being given to the structure of their catching webs.
The webs of Latrodectus represent a further development of the web-type of Archaeranea tepidariorum . The specific characters of the investigated webs concern the middle layer of their three-layer webs, where more or less regular structures appear.
In the middle layer of L. tredecimguttatus web paths of hexagonal meshes appear.
In the web of L. pallidus and L. revivensis more or less regular radially arranged catching platforms appear, connected with the distant retreat by a long bridge-web.
The lower layer of vertical threads, with viscid droplets on their far ends is spread-out in L. tredecimguttatus and consists of short threads as distinct from the concentrated bundle of high threads in the two other species.
Since L. pallidus and L. revivensis appear usually among vegetation, their restricted catching webs seem to be adaptive adjustment to the biotope.
The concentration of the catching webs brings about improvement as regards prey detection.
The differences in the web structure of L. tredecimguttatus and L. revivensis indicate that their behavioural characters are more distinct than the morphological ones. The different behavioural characters support the view that L. revivensis represents a species different from L. mactans tredecimguttatus .     

The effects of temperature on the web-building behaviour of the common house spider, Achaearanea tepidariorum

1. Because spiders are ectothermic animals, the temperature regime of the microhabitat in which an individual finds itself may affect important performance traits of that individual. The present study examined the effects of temperature on attributes of webs spun by Achaearanea tepidariorum (C. L. Koch), as well as testing temperature preference in this species. The effects of temperature on the amount of silk per web produced by Achaearanea tepidariorum and the prey-capture efficiency of webs produced at different temperatures were determined by using webs constructed at 5, 10, 15, 20, 25 and 30°C. The temperature preferences of A. tepidariorum within a thermal gradient were also determined.
2. Web mass was related to temperature, exhibiting a quadratic relation with a maximum web mass occurring at approximately 20°C.
3. Number of strands per cm³ of webs varied directly with web mass; webs with greater strand densities were more efficient at capturing flies.
4. The number of spiders observed in each temperature range in the thermal gradient indicated a non-uniform distribution, with the spiders avoiding temperatures in the highest range (27·3±2·0°C).
5. These data suggest an optimal temperature for web construction at which webs produced are more efficient at capturing prey. The data also suggest that this species may avoid sites that do not provide an adequate thermal environment.     

Vertical asymmetries in orb webs

In almost all vertical orb webs the hub is above the geometric centre and consequently, the extent of the capture area is larger below the hub than above. In addition to this vertical web‐extent asymmetry, orb webs show vertical asymmetries in number of spiral loops, mesh widths, and angles between radii. However, it was unknown whether these asymmetries are adaptations to the web‐extent asymmetry or whether they are linked to gravity in a different way than through web‐extent asymmetry. We reviewed known vertical asymmetries of orb webs, and we analysed the asymmetries of webs built by four different Cyclosa species, which show large intra‐ and inter‐specific variation in web‐extent asymmetry. We found all analysed structural asymmetries to be linked both to web‐extent asymmetry and to gravity: Larger web extents below the hub and gravity both led to more sticky‐spiral loops and to smaller angles between radii below the hub, whereas web‐extent asymmetry and gravity had opposing effects on mesh width (mean and peripheral). Independent of web‐extent asymmetry, almost all analysed webs had narrower peripheral meshes and smaller angles between radii below the hub than above. We interpret the narrow peripheral meshes along the web's lower edge as an adaptation to prevent tumbling prey from escaping, and the small angles between radii as an adaptation to prevent the sticky‐spiral lines in these narrow meshes to come into contact with each other. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 659–672.     

Fine structure of sheet-webs of Linyphia triangularis (Clerck) and Microlinyphia pusilla (Sundevall), with remarks on the presence of viscid silk

We examined the webs of Linyphia triangularis (Clerck) and Microlinyphia pusilla (Sundevall) using light and scanning electronic microscopic techniques and compared them with the better known orb‐webs. The linyphiid sheet‐web consists of an unordered meshwork of fibres of different thicknesses. The sheet is connected to the scaffolding by means of attachment discs. Thin threads with globules, which appear similar to the viscid silk droplets of orb‐webs, are present in most webs examined. Webs of M. pusilla had a higher density of these globules than did webs of L. triangularis. Webs of both species possess five types of thread connections and contain no aqueous glue for prey capture. Instead, unlike orb‐webs, the sticky substances produced by the linyphiid aggregate glands cement the different layers and threads of the sheet by drying up after being produced. Due to their function, sheet webs may not require viscid silk, thereby leading to a more economic web. The assumption made in most previous studies, that the globules in linyphiid webs have the same properties and function as viscid silk in orb‐webs, is unfounded.     

Environmentally induced post‐spin property changes in spider silks: influences of web type,spidroin composition and ecology

Many spiders use silk to construct webs that must function for days at a time, whereas many other species renew their webs daily. The mechanical properties of spider silk can change after spinning under environmental stress, which could influence web function. We hypothesize that spiders spinning longer‐lasting webs produce silks composed of proteins that are more resistant to environmental stresses. The major ampullate (MA) silks of orb web spiders are principally composed of a combination of two proteins (spidroins) called MaSp1 and MaSp2. We expected spider MA silks dominated by MaSp1 to have the greatest resistance to post‐spin property change because they have high concentrations of stable crystalline β‐sheets. Some orb web spiders that spin three‐dimensional orb webs, such as Cyrtophora, have MA silks that are predominantly composed of MaSp1. Hence, we expected that the construction of three‐dimensional orb webs might also coincide with MA silk resistance to post‐spin property change. Alternatively, the degree of post‐spin mechanical property changes in different spider silks may be explained by factors within the spider's ecosystem, such as exposure to solar radiation. We exposed the MA silks of ten spider species from five genera (Nephila, Cyclosa, Leucauge, Cyrtophora, and Argiope) to ecologically high temperatures and low humidity for 4 weeks, and compared the mechanical properties of these silks with unexposed silks. Using species pairs enabled us to assess the influence of web dimensionality and MaSp composition both with and without phylogenetic influences being accounted for. We found neither the MaSp composition nor the three‐dimensionality of the orb web to be associated with the degree of post‐spin mechanical property changes in MA silk. The MA silks in Leucauge spp. are dominated by MaSp2, which we found to have the least resistance to post‐spin property change. The MA silk in Argiope spp. is also dominated by MaSp2, but has high resistance to post‐spin property change. The ancestry of Argiope is unresolved, but it is largely a tropical genus inhabiting hot, open regions that present similar stressors to silk as those of our experiment. Ecological factors thus appear to influence the vulnerability of orb web spider MA silks to post‐spin property change. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 580–588.     

Why cross the web: decoration spectral properties and prey capture in an orb spider (Argiope keyserlingi) web

An effective visual signal elicits a strong receiver response. The visual receptors of most insects are sensitive to ultraviolet (UV), blue and green light. The decorations of certain orb web spiders may be described as a type of visual signal, a sensory trap, as they exploit visual biases in insects. We filtered UV and blue light from the decorations of Argiope keyserlingi , under field conditions, using plastic sheets to test if the UV and blue light reflected affects the type of prey caught. We found that houseflies, blowflies, stingless bees, honeybees and vespid wasps were caught more frequently in webs with decorations than webs without, while ichneumonid wasps were caught less frequently. Blowflies, stingless bees, honeybees and vespid wasps were caught more often in unfiltered decorated webs. These insects also have receptor sensitivities in the blue and UV. We showed that exploiting visual sensory biases plays an integral role in attracting insects to orb web decorations. Whether UV light, blue light, or both, are the most important cue, however, requires further study.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 221–229.     

An exuberant, undescribed colour polymorphism in Theridion californicum (Araneae, Theridiidae): implications for a theridiid pattern ground plan and the convergent evolution of visible morphs

An opisthosomal (abdominal) colour polymorphism is described in the North American spider, Theridion californicum , comprising a plain Yellow morph and (at least) ten patterned morphs, which exhibit areas of red or black pigments superimposed on the yellow background, or no pigment (white). The polymorphism appears to be present throughout the species' range. The Yellow morph is the most frequent in populations, with patterned morphs all, individually, being rather rare. Progeny from known mothers were reared and indicate that the polymorphism is genetic and that Yellow is probably recessive to patterned morphs. Similar to other theridiids with well-studied colour polymorphisms, T. californicum occupies an under-leaf habitat and the variation in all these cases might be maintained by sight-hunting predators exerting negative frequency-dependent (apostatic) selection. In T. californicum , blocks of guanine underlying the pigmented hypodermis indicate a segmental patterning, which is not usually apparent in adult spiders. These segments, plus dorso-lateral divisions, permit the dorsal surface of the opisthosoma to be divided up into two mirror-image halves, each comprising 12 compartments. Each compartment can either lack pigment (thus appearing white as a result of underlying guanine) or be yellow, red, or black. All patterns in T. californicum can be derived from this ground plan, as can the morphs of other colour-polymorphic theridiids. It is suggested that selection for polymorphism, combined with constraints imposed by this theridiid ground plan, may have led to the convergent evolution of colour patterns across the family.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 23–34.     

Phylogenetic position and composition of Zygiellinae and Caerostris,with new insight into orb‐web evolution and gigantism

Orb‐weaving spiders are good objects for evolutionary research, but phylogenetic relationships among and within orb‐weaving lineages are poorly understood. Here we present the first species‐level molecular phylogeny that includes the enigmatic orb weavers ‘Zygiellidae’ and Caerostris. Zygiellidae is interesting for the evolution of the sector web, and Caerostris is noteworthy for web gigantism and extraordinary silk biomechanics. We assembled a molecular data set using mitochondrial (COI, 16S) and nuclear (H3, 18S, 28S, ITS2) gene fragments for 112 orbicularian exemplars, focusing on taxa with diverse web architecture and size. We show that ‘Zygiellidae’ contains the Holarctic Zygiella genus group (Leviellus, Parazygiella, Stroemiellus, and Zygiella) and the Australasian Phonognatha and Deliochus. As this clade is placed with Araneidae in all analyses we treat it as a subfamily, Zygiellinae. Using the new phylogeny, we show that the sector web evolved eight times, and coevolved with the silk tube retreat, but that these features are not zygielline synapomorphies. Zygiellinae, Caerostris, and some other araneids form a basal grade of araneids that differ from ‘classical’ araneids in web‐building and preying behaviour. We also confirm that Caerostris represents the most striking case of spider‐web gigantism. © 2015 The Linnean Society of London     

Behavioural and biomaterial coevolution in spider orb webs

Mechanical performance of biological structures, such as tendons, byssal threads, muscles, and spider webs, is determined by a complex interplay between material quality (intrinsic material properties, larger scale morphology) and proximate behaviour. Spider orb webs are a system in which fibrous biomaterials—silks—are arranged in a complex design resulting from stereotypical behavioural patterns, to produce effective energy absorbing traps for flying prey. Orb webs show an impressive range of designs, some effective at capturing tiny insects such as midges, others that can occasionally stop even small birds. Here, we test whether material quality and behaviour (web design) co‐evolve to fine‐tune web function. We quantify the intrinsic material properties of the sticky capture silk and radial support threads, as well as their architectural arrangement in webs, across diverse species of orb‐weaving spiders to estimate the maximum potential performance of orb webs as energy absorbing traps. We find a dominant pattern of material and behavioural coevolution where evolutionary shifts to larger body sizes, a common result of fecundity selection in spiders, is repeatedly accompanied by improved web performance because of changes in both silk material and web spinning behaviours. Large spiders produce silk with improved material properties, and also use more silk, to make webs with superior stopping potential. After controlling for spider size, spiders spinning higher quality silk used it more sparsely in webs. This implies that improvements in silk quality enable ‘sparser’ architectural designs, or alternatively that spiders spinning lower quality silk compensate architecturally for the inferior material quality of their silk. In summary, spider silk material properties are fine‐tuned to the architectures of webs across millions of years of diversification, a coevolutionary pattern not yet clearly demonstrated for other important biomaterials such as tendon, mollusc byssal threads, and keratin.     

Female false black widow spiders,Steatoda grossa,recognize webs based on physical and chemical cues

Females of the false black widow, Steatoda grossa CL Koch (Araneae: Theridiidae), invest significant energy and time weaving cobwebs. We tested the hypothesis that S. grossa females select sites for their webs based, in part, on the presence of con‐ or heterospecific webs, sensing both physical and chemical web cues. In bioassays, we offered female S. grossa a choice between an empty control frame and a frame bearing the web of a conspecific female or that of a female common house spider, Parasteatoda tepidarium CL Koch (Araneae: Theridiidae), recording (1) the time she spent, and (2) the time she spent inactive (a proxy for settling behaviour) on each frame. We also tested the effect of (1) silk micro‐ and macrostructure (wrapped‐up silk or intact web, each semiochemical‐deprived), (2) plastic webs, and (3) silk semiochemical extract on the responses of S. grossa females. Females settled on both con‐ and heterospecific webs and chose test stimuli based on their chemical and physical characteristics. Even plastic webs in cobweb‐like arrangement readily prompted settling behaviour by females. Our results suggest that web architecture, rather than web silk, mediates settling responses by female S. grossa on pre‐existing webs which may provide structural support for a new web and indicate habitat suitability.     

The common house spider alters the material and mechanical properties of cobweb silk in response to different prey

Many spiders depend upon webs to capture prey. Web function results from architecture and mechanical performance of the silk. We hypothesized that the common house spider, Achaearanea tepidariorum, would alter the mechanical performance of its cobweb in response to different prey by varying the structural and material properties of its silk. We fed spiders either large, high kinetic energy crickets or small, low kinetic energy pillbugs for 1 week and then examined their freshly spun silk. We separated mechanical performance into structural and material effects. We measured both types of properties for silk threads collected directly from cobwebs to test for "tuning" of silk performance to different aspects of prey capture. We compared silk from two different functional regions of the cobweb-sticky gumfooted threads that adhere directly to prey and supporting threads that maintain web integrity. Supporting threads from cricket-fed spiders were stiffer and tougher than supporting threads from pillbug-fed spiders. Both types of silk from cricket-fed spiders broke at higher loads than silk from pillbug-fed spiders. We explain this variation using a simple model of forces exerted by prey and spiders on single threads and propose potential mechanisms for this change in material properties. Two alternative, nonexclusive, hypotheses are suggested by our data. Spiders may tune silk to different types of prey by spinning threads that are able to hold prey without deforming permanently. Alternatively, as spider's body mass differed dramatically between the two feeding regimes, spiders may tune silk to their own body mass.     

Female morphology,web design,and the potential for multiple mating in Nephila clavipes: do fat‐bottomed girls make the spider world go round?

In animal species where females mate with multiple males, female mating success might be expected to covary with aspects of female morphology, such as size or shape. Spiders are especially interesting in this regard, as the females of several spider groups weave intricate webs that often accommodate multiple male spiders, all of whom are potential mates. Because web design is likely to be dependent on female size/shape, we use multivariate methods to assess the relationships among female morphology, web design, and reproductive ecology over a range of body sizes in the orb-weaving spider Nephila clavipes . Of the measured variables, only abdomen size explained a significant amount of the variation in number of males on a web, and this relationship holds even after statistically accounting for body size. Because abdomen size is an indicator of body condition in spiders, we suggest that condition is likely to be an important factor relating to potential mating success in female spiders. We found no evidence for an association between web design and number of males on a web, although our data indicate that larger females build webs that are both larger and further from the ground than those of smaller females.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87 , 95−102.     

Conspecific and Heterospecific Attraction: A Mechanism of Web-site Selection Leading to Aggregation Formation by Web-building Spiders

This study investigated whether conspecific and/or heterospecific attraction to silk is a mechanism of web-site selection leading to aggregation formation by two species of web-building spiders, Hypochilus thorelli Marx (Araneae: Hypochilidae) and Achaearanea tepidariorum (C.L. Koch) (Araneac: Theridiidae). We determined that the spatial distribution of these two spiders was clumped and that H. thorelli had a greater tendency to aggregate than did A. tepidariorum. To determine the mechanism responsible for this spatial pattern, we conducted three field experiments. We examined web-site selection by H. thorelli in three contexts: no spiders or webs present (cue removed), vacant webs present, and occupied webs present. In the case where no webs were present, there was no tendency for spiders to choose previously occupied sites as web sites. When vacant webs were present, spiders chose to occupy the vacant webs. When occupied webs were present, spiders either invaded webs and evicted the owners, or settled adjacent to and attached their webs to those of residents. Various microhabitat variables (height, angle, temperature, humidity, and substrate character of the rock surface) of randomly selected unoccupied sites and the web sites chosen by spiders were compared. There were no detectable differences between web sites and unoccupied sites with respect to any of the variables measured. This leads us to conclude that web-site choice by immigrating spiders was based on the presence of silk rather than other features of the site.     

Homology, behaviour and spider webs: web construction behaviour of Linyphia hortensis and L. triangularis (Araneae: Linyphiidae) and its evolutionary significance

Linyphiidae is the second largest family of spiders. Using Linyphia hortensis and L. triangularis, we describe linyphiid sheet-web construction behaviour. Orb-web construction behaviour is reviewed and compared with that of nonorb-weaving orbicularians. Phylogenetic comparisons and the biogenetic law are applied to deduce behavioural homology. Linyphia webs were constructed gradually and in segments over a period of many days and had a long lifespan. Two construction behaviours, supporting structure and sticky thread (ST) (within the sheet) were observed. ST construction behaviour in linyphiids is considered homologous to sticky spiral construction in orb-weavers. Overall web construction conformed to the pattern of alternate construction of sticky and nonsticky parts as observed in theridiids. Linyphiids had no problem in switching between structure construction and ST construction even during a single behavioural bout. Both web construction behaviours in linyphiids were nonstereotypic, which is unusual in orbicularians. This might be due to the loss of control mechanisms at genetic level, probably by macro mutation. Lack of stereotypic behaviour might have played a substantial role in the origin of the diverse web forms seen in nonorb-weaving orbicularians. This hypothesis is consistent with patterns observed in the orbicularian phylogeny.     

Stabilimenta of Philoponella vicina (Araneae: Uloboridae) and Gasteracantha cancriformis (Araneae: Araneidae): Evidence Against a Prey Attractant Function

Both the uloborid Philoponella vicina and the araneid Gasteracantha cancriformis spiders sometimes placed silk stabilimenta on non-orb "resting webs" that consisted of only one or a few lines. These webs completely lacked sticky silk, so their stabilimenta could not function to attract prey. Some non-orbs were built by spiders when their orb webs are damaged. These observations contradict the prey attraction camouflage hypothesis for stabilimentum function, but are compatible with the spider camouflage and web advertisement to avoid web destruction hypotheses.