Biodiversity of orb-web spiders (family: araneidae) of buner valley, Pakistan

The present research was carried out to explore the spider fauna of Buner valley with taxonomic study from February 2018 to January 2019. For this purpose samples were collected, four times at each month from 4 tehsils: Daggar, Gagra, Mandan and Totalai. Two methods were used, hand picking and sweep net for collection of samples. During day and night, three habitats, arid area, agriculture land and building area were search for collection. A total of 534 samples of spider were collected from four sampling sites, in which 379 were belonging to family Araniedae. After confirmation, the identified species were belonging to 8 genera (Neoscona, Argiope, Cyclosa, Araneus, Cyrtophora, Larinia, Erivoxia and Poltys) and 19 species. 18 of them were identified to specie level while a single specie to its generic level. The genus Neoscona was the dominant genus 26.31% having 5 species while the genus Argiope 21.05% is the second dominant having 4 species followed by Cyclosa 15.78% having 3 species followed by Cyrtophora and Araneus 10.52% having two species both. The Poltys and Larinia 5.26% are the rarest genera represent single-single specie both. Statistical analysis show that specie richness (D) = 5.77, Simpson index (1-D) = 0.87, Shannon index (H) = 2.33. Diversity of spiders was evenly distributed and calculated Evenness value was H/InS = 0.5408. There is also few atypical species and Fisher alpha estimate high value (Fisher α) = 4.42. Chao-1 estimated we have reported 22 species.

Shaped by the Sun: the effect of exposure to sunlight on the evolution of spider bodies

Body temperature can strongly influence fitness. Some Sun-exposed ectotherms thermoregulate by adjusting body posture according to the Sun's position. In these species, body elongation should reduce the risk of heat stress by allowing the exposure of a smaller body area to sunlight. Therefore, selection should favour more elongated bodies in Sun-exposed than in Sun-protected species. Diurnal orb-web spider species that sit on their webs are more likely to be Sun-exposed, on average, than nocturnal or diurnal shelter-building species. We measured the body elongation of orb-web spiders (Araneae, Araneidae) across 1024 species and classified them as Sun-protected or exposed based on the literature. We found that Sun-exposed species evolved more elongate bodies than Sun-protected ones. Further, we built a model combining traditional heat transfer models with models of thermoregulatory postures in orb-web spiders and meteorological data. The model indicates that body elongation in large orb-web spiders decreases the risk of high body temperatures. Overall, our results suggest that Sun exposure influenced the evolution of body shapes of orb-web spiders.

Dynamic environments do not appear to constrain spider web building behaviour

Many laboratory experiments demonstrate how orb-web spiders change the architecture of their webs in response to prey, surroundings and wind loading. The overall shape of the web and a range of other web parameters are determined by frame and anchor threads. In the wild, unlike the lab, the anchor threads are attached to branches and leaves that are not stationary but move, which affects the thread tension field. Here we experimentally test the effect of a moving support structure on the construction behaviour and web-parameters of the garden cross spider Araneus diadematus. We found no significant differences in building behaviour between rigid and moving anchors in total time spent and total distance covered nor in the percentage of the total time spent and distance covered to build the three major web components: radials, auxiliary and capture spirals. Moreover, measured key parameters of web-geometry were equally unaffected. These results call for re-evaluation of common understanding of spider webs as thread tensions are often considered to be a major factor guiding the spider during construction and web-operation.

Eco-localization of a prey in a spider orb web

Orb web spiders locate the position of a perturbation in the web because of a prey impact through highly sensitive slit sensilla at the tip of their legs. Thus, the web serves as a self-made extension of its sensory space which transmits vibrations from the perturbation point to the spider location. These vibrations may contain the information required by the spider to rapidly identify the position where the prey has impacted and approach to it before it flies away. For axially symmetric orb webs supported at the boundary and for a spider which stays at the center of the web, it was shown that the knowledge of the transverse deflection time history at the eight spider legs, for a sufficiently large interval of time, contains enough information to localize the position of the prey. In this article, we address the same inverse problem of localization of the prey, but we suppose that the spider knows only a small number of selected information of the transverse displacement, such as, for example, the maxima of the response of the time history at the eight control points. We show how this reduced information still allows the spider to obtain a fairly accurate angular localization of the prey, for different prey and orb web characteristics.

Spider webs inspiring soft robotics

In soft robotics, bio-inspiration ranges from hard- to software. Orb web spiders provide excellent examples for both. Adapted sensors on their legs may use morphological computing to fine-tune feedback loops that supervise the handling and accurate placement of silk threads. The spider's webs embody the decision rules of a complex behaviour that relies on navigation and piloting laid down in silk by behaviour charting inherited rules. Analytical studies of real spiders allow the modelling of path-finding construction rules optimized in evolutionary algorithms. We propose that deconstructing spiders and unravelling webs may lead to adaptable robots able to invent and construct complex novel structures using relatively simple rules of thumb.

Color lures in orb-weaving spiders: a meta-analysis

Lures are deceptive strategies that exploit sensory biases in prey, usually mimicking a prey’s mate or food item. Several predators exploit plant–pollinator systems, where visual signals are an essential part of interspecific interactions. Many diurnal, and even nocturnal, orb-web spiders present conspicuous body coloration or bright color patches. These bright colors are regarded as color-based lures that exploit biases present in insect visual systems, possibly mimicking flower colors. The prey attraction hypothesis was proposed more than 20 years ago to explain orb-web spider coloration. Although most data gathered so far has corroborated the predictions of the prey attraction hypothesis, there are several studies that refute these predictions. We conducted a multilevel phylogenetic meta-analysis to assess the magnitude of the effect of conspicuous orb-web spider body coloration on prey attraction. We found a positive effect in favor of the prey attraction hypothesis; however, there was substantial heterogeneity between studies. Experimental designs comparing conspicuous spiders to painted spiders or empty webs did not explain between-studies heterogeneity. The lack of theoretical explanation behind the prey attraction hypothesis makes it challenging to address which components influence prey attraction. Future studies could evaluate whether color is part of a multicomponent signal and test alternative hypotheses for the evolution of spider colors, such as predator avoidance and thermoregulation.