Web-building Spiders Research Articles

Transformation of dry dipterocarp to dry evergreen forests alters food webs of web-building spiders and their prey

Anthropogenic habitat modification is a major contributor to global change. While the modification of natural habitats to agroecosystems attracts most of the attention, little is known about the conversion of one natural ecosystem to another. Dry dipterocarp forest is the key dry forest type across Southeast Asia. Moderate fire disturbance is essential for its regeneration, but humans often prevent fire in these forests. Consequently, dry dipterocarps can change to dry evergreen forests through succession. The consequences of this conversion on food webs are unknown. Using the network approach, we compared the food webs of web-building spiders and their prey in the understory between dry dipterocarp (open canopy, uniform understory) and dry evergreen forests (closed canopy, heterogeneous understory) in north-eastern Thailand. Overall, we collected 560 individual web-building spiders belonging to 37 genera. Further, we collected 1139 prey items from spider webs belonging to 16 arthropod orders. The composition of captured prey and the network structure differed between the forest types. Specifically, the web-building spiders were more specialized and their niches overlapped less in dry dipterocarps than in dry evergreens. The differences in food-web structure were driven mostly by trophic groups turnover rather than interaction rewiring. Implications for insect conservation: The transformation of dry dipterocarp to dry evergreen forests from the prevention of fire disturbance may lead to an altered ecological function of web-building spiders in forest understories. As trophic links and their strength are rewired, habitat modification may also lead to changes in nutrient and energy flow in forest understories.

Colour polymorphism is prevalent on islands but shows no association with range size in web-building spiders.

One of the most evident sources of phenotypic diversity within a population is colouration, as exemplified by colour polymorphism. This is relevant to a greater extent in animals with visually-biased sensory systems. There is substantial evidence suggesting that different colour morphs can access a broader range of habitats or niches, leading to larger geographic range sizes. However, this hypothesis has been tested in few lineages, comprising species where colour is likely to be involved in sexual selection. Furthermore, some available evidence considers geographical variation as polymorphism, thus limiting our comprehension of how sympatric colour polymorphism can influence a species' geographic range. Through an extensive systematic literature review and a comparative analysis, we examined the relationship between colour polymorphism and range size or niche breadth in web-building spiders. We identified 140 colour polymorphic spider species, belonging mainly to the families Araneidae and Theridiidae. We found no evidence that colour polymorphic species differ significantly from non-polymorphic species in terms of range size and niche breadth, after accounting for phylogenetic relationships and other covariates. However, we did observe that colour polymorphic species were more likely to be found on islands compared to non-polymorphic species. Overall, our results indicate that the association between colour polymorphism and geographic range size may not exist among web-building spiders, or be as pronounced as in other lineages. This suggests that the strength of the association between colour polymorphism and ecological success might depend on the ecological role that colouration plays in each clade.

Disguise or surprise: spider antipredator adaptations as a function of the architecture of their webs

Abstract Animals exhibit a variety of strategies to avoid predation; spiders are no exception. We explored whether web-building spiders that differ in the architecture of their webs exhibit morphologies or behaviors suggestive of antipredator strategies that trade-off with the degree of protection offered by their webs. Spiders build webs of 3 types: the more protected tangles and sheet-and-tangles, which are three-dimensional (3D), and the more exposed orbs, which are two-dimensional (2D), both with or without a refuge. We hypothesize that spiders whose webs offer greater protection—a 3D architecture or a refuge—will be less likely to be armored or brightly colored when compared to spiders without these protections. We collected data on 446 spiders and their webs in 2 lowland tropical rainforest sites. We show that 2D web builders with no refuges tended to be brightly colored (background contrasting) and spiny (spiky), whereas those with refuges tended to blend against the background of their refuges. 3D web builders, on the other hand, were neither cryptic nor brightly colored nor armored but were more likely to drop out of the web upon simulated predator contact. These results support the hypothesis that web-building spiders tend to be protected either through the architecture of their webs or their morphology and behavior, suggesting a trade-off between different types of antipredator strategies.

Effects of artificial night lighting on a web-building spider species in urban green spaces

Urban green spaces are biological habitats that play an important role in maintaining urban biodiversity and are affected by artificial light at night (ALAN). Determining the effects of ALAN on predators in urban green spaces is important for promoting the maintenance and conservation of these functions of insect communities in urban green spaces. We investigated the effects of ALAN on a web-building spider species (Trichonephila clavata) in urban green spaces in the Tokyo metropolitan area, Japan. We used a GPS receiver to determine the positions of streetlights and spider webs and classified the webs into two groups: those within the reach of streetlights and those outside their range. We then measured the web distribution (web density), web size, female traits (femur length and body weight), and male presence. Web densities in the light conditions were higher and web sizes smaller than those of webs in the no light conditions. Female body weight and length were also significantly lower in the light conditions than in the no light conditions. However, female body condition and male abundance did not differ between the light and no light conditions. Our results showed that T. clavata maintains some degree of fitness in urban fragmented green spaces although their physical characteristics and behaviour are altered by ALAN. Therefore, we suggest that measures to improve the quality within green infrastructure are required to maintain the function of generalist predators such as web-building spiders in urban green spaces.

Changes in community composition and prey capture of web-building spiders during rice field development

Understanding the effects of microhabitat changes on arthropod predator communities and their prey in agroecosystems is essential for field management and biocontrol. Few studies have investigated the trait composition of web-building spider communities in rice ecosystems. Here, we examined how temporal changes during the rice field development affect the abundance and traits of orb-web spiders, and how these effects consequently influence captured prey number and prey composition in irrigated rice ecosystems in southern Thailand. We used structural equation models to evaluate direct and indirect, spider-mediated effects of rice field development on captured prey numbers in each different guild. We found that the number of horizontal web-building spiders decreased during the rice field development, whereas there was no significant change in number of vertical web-building spiders. The number of captured detritivorous insects was positively related to the numbers of horizontal and vertical web-building spiders, while phytophagous insects and others were positively related only to the numbers of vertical web-building spiders. Moreover, the prey number captured by vertical web-building spiders seems to be indirectly increased through the decreasing number of horizontal web-building spiders in the late rice season. A fourth-corner analysis showed that spider species identity, spider traits (web type, web height and web diameter), vegetation height, and water level generally influenced the prey captured by web-building spiders. Horizontal web-building spider species with lower web placement during the flooding phase captured high numbers of detritus-feeding insects, while vertical web-building spider species with higher web placement captured high numbers of rice pests, predators and others. Our results suggest that the field development acted as an environmental factor that determined the species identity and traits of web-building spider communities. The findings of this study can help to predict the ecosystem services provided by the web-building spider community in rice ecosystems.

Identification and Evolutionary Analysis of the Widely Distributed CAP Superfamily in Spider Venom.

Venom plays a crucial role in the defense and predation of venomous animals. Spiders (Araneae) are among the most successful predators and have a fascinating venom composition. Their venom mainly contains disulfide-rich peptides and large proteins. Here, we analyzed spider venom protein families, utilizing transcriptomic and genomic data, and highlighted their similarities and differences. We show that spiders have specific combinations of toxins for better predation and defense, typically comprising a core toxin expressed alongside several auxiliary toxins. Among them, the CAP superfamily is widely distributed and highly expressed in web-building Araneoidea spiders. Our analysis of evolutionary relationships revealed four subfamilies (subA-subD) of the CAP superfamily that differ in structure and potential functions. CAP proteins are composed of a conserved CAP domain and diverse C-terminal domains. CAP subC shares similar domains with the snake ion channel regulator svCRISP proteins, while CAP subD possesses a sequence similar to that of insect venom allergen 5 (Ag5). Furthermore, we show that gene duplication and selective expression lead to increased expression of CAP subD, making it a core member of the CAP superfamily. This study sheds light on the functional diversity of CAP subfamilies and their evolutionary history, which has important implications for fully understanding the composition of spider venom proteins and the core toxin components of web-building spiders.

Heuristic test reveals little effect of learning and maturation on early prey capture experiences in a web-building spider

Behaviors can vary throughout an animal’s life and this variation can often be explained by changes associated with learning and/or maturing. Currently, there is little consensus regarding how these processes interact to affect behaviors. Here we proposed a heuristic approach to disentangle the effects of learning and maturation on behavior and applied it to the predatory behaviors of Physocyclus globosus spiderlings. We varied the degree of prey difficulty and familiarity spiderlings received along the first instar and across the molt to the second instar and quantified the time spiderlings spent wrapping prey, as a proxy for prey capture efficiency. We found no overall evidence for learning or maturation. Changes in efficiency were mainly due to the switch from difficult to easy prey, or vice versa. However, there was one treatment where spiderlings improved in efficiency before and after the molt, without a switch in prey type. This provides some indication that difficult prey may offer more opportunity for learning or maturation to impact behavior. Although we found little effect of learning or maturation on prey capture efficiency, we suggest that our heuristic approach is effective and could be useful in investigating these processes in other behaviors and other animals.

How dispersal rates depend on the prey capture strategy: A case study of Georgia's spiders.

Large-scale barcoding projects help to aggregate information on genetic variability of multiple species throughout their ranges. Comparing DNA sequences of both non-conspecific and conspecific individuals from distant parts of their ranges helps to compare level of genetic isolation-by-distance patterns in different species and adaptive types. We compared mitochondrial CO1 gene sequences of 223 spiders from Georgia (Caucasus), representing 124 species and eight families, with 3097 homological sequences from spiders mostly from Europe, but also from other parts of the World. In most families, a significant isolation-by distance pattern was observed on family level. On species level, a significant isolation-by-distance was observed in 40 species, although this low proportion is most likely related to a lack of data. Simultaneously, remarkable differences in spatial structure were shown for different species. Although the majority of the studied species have a broad western Palearctic range, web-building spiders from families Araneidae, Theridiidae, and Linyphiidae are less isolated spatially than flower spiders (Thomisidae), jumping spiders (Salticidae), wolf spiders (Lycosidae), sac spiders (Clubionidae), and ground spiders (Gnaphosidae). This pattern is related with more common ballooning in web building than in actively hunting spiders, which commonly remain isolated since preglacial time. Ground spiders build the most isolated populations in the Caucasus.

Web-building spiders and blood-feeding flies as prey of the notch-eared bat (Myotis emarginatus)

Conservation of the endangered notch-eared bat (M. emarginatus) requires a specific action plan based on precise ecological requirements of this species. The analysis of the diet of three colonies in southern Belgium revealed: (1) spatial and seasonal variations of the diet; (2) the consumption of web-building spiders (Araneus diadematus, Araneus triguttatus, Cyclosa conica, Enoplognatha sp., Larinioides patagiatus, Neriene emphana); (3) the predominance of blood-feeding dipterans in the diet (Stomoxys calcitrans and Musca autumnalis). Since the populations of these two ectoparasitic flies are sensitive to the use of antiparasitic drugs, these drugs should be used with caution by farmers and veterinarians in the vicinity of maternity colonies.

Discovery of Web-Building Spiders in Gua Kelam, Perlis State Park, Malaysia.

A cave represents a subterranean ecosystem that harbours a myriad of unique, peculiar, and secluded flora and fauna. These biotas have evolved with a wide range of ecological adaptations that allow them to thrive in harsh environments with limited light. Gua Kelam 1 constitutes part of the Gua Kelam limestone caves system in the Nakawan Range of Perlis State Park, Malaysia. Previous observations indicated that it harbours a plethora of spider species; however, their existence is still elusive as speleobiological studies remain unexplored. Herein, we identified the cavernicolous spiders found in the dark zone areas of Gua Kelam 1 through a complementary approach based on morphology and DNA barcoding. From the morphological analysis, we described three web-building spiders of JTKK2 and JTKK3 groups down to the species-level to belong to Nephilengys malabarensis, and Orsinome vethi except for Pholcus sp. from JTKK4 individuals. The molecular analysis of the cytochrome oxidase-I (COI) genes of JTKK2 and JTKK3 individuals showed that they exhibited a high degree similarity with N. malabarensis (98.3%), and O. vethi (100.0%), respectively except for JTKK4 individuals with only 91.4% homology with P. kuhapimuk. Phylogenetic analysis also generated a congruent tree, in which the identified species are well nested within the family Araneidae, Tetragnathidae, and Pholcidae. By this integral approach, the three spiders were determined as N. malabarensis, O. vethi, and Pholcus sp. These spiders are originally epigean in their habitat but uniquely thrive in Gua Kelam 1.

Unrevealing components of risk assessment: escape behaviour and refuge use in a web-building spider

Unrevealing components of risk assessment: escape behaviour and refuge use in a web-building spider

Single-cell transcriptomics reveals the brain evolution of web-building spiders

Spiders are renowned for their efficient capture of flying insects using intricate aerial webs. How the spider nervous systems evolved to cope with this specialized hunting strategy and various environmental clues in an aerial space remains unknown. Here we report a brain-cell atlas of >30,000 single-cell transcriptomes from a web-building spider (Hylyphantes graminicola). Our analysis revealed the preservation of ancestral neuron types in spiders, including the potential coexistence of noradrenergic and octopaminergic neurons, and many peptidergic neuronal types that are lost in insects. By comparing the genome of two newly sequenced plesiomorphic burrowing spiders with three aerial web-building spiders, we found that the positively selected genes in the ancestral branch of web-building spiders were preferentially expressed (42%) in the brain, especially in the three mushroom body-like neuronal types. By gene enrichment analysis and RNAi experiments, these genes were suggested to be involved in the learning and memory pathway and may influence the spiders’ web-building and hunting behaviour. Our results provide key sources for understanding the evolution of behaviour in spiders and reveal how molecular evolution drives neuron innovation and the diversification of associated complex behaviours.

Widow spiders alter web architecture and attractiveness in response to same-sex competition for prey and mates, and predation risk

Female-female competition in animals has rarely been studied. Responses of females that compete context-dependently for mates and prey, and seek safety from predators, are ideally studied with web-building spiders. Cobwebs possess unique sections for prey capture and safety, which can be quantified. We worked with Steaoda grossa females because their pheromone is known, and adjustments in response to mate competition could be measured. Females exposed to synthetic sex pheromone adjusted their webs, indicating a perception of intra-sexual competition via their sex pheromone. When females sequentially built their webs in settings of low and high intra-sexual competition, they adjusted their webs to increase prey capture and lower predation risk. In settings with strong mate competition, females deposited more contact pheromone components on their webs and accelerated their breakdown to mate-attractant pheromone components, essentially increasing their webs’ attractiveness. We show that females respond to sexual, social and natural selection pressures originating from intra-sexual competition.

Land planarians (Platyhelminthes) also prey on web-building spiders

Although spiders and land planarians constitute diverse groups of terrestrial predators, interactions between them are still unknown. Here, we describe a predatory event of a land planarian (Choeradoplana cf. gladismariae) on a web-building spider (Helvibis longicauda) in the Brazilian Atlantic Forest. The prey was constricted and covered with sticky mucus while remaining on its web trying to protect its egg sac. The event was observed in the middle-end afternoon at ca. 1.80 m height. Our observation broadens the scope of possible natural enemies of web-building spiders and the prey items of land planarians. It also indicates that these organisms can capture and overpower dangerous predatory arthropods, suggesting that even complex three-dimensional sticky webs can be ineffective against the attack of land planarians. Finally, we also show that land planarians can exhibit a flexible foraging strategy, exploiting the environment during the day and at higher heights from the ground. Our observation opens new possibilities involving focal observations and experiments using spiders and land planarians as models in predator-prey research.

Effects of land use and climate on web-building spiders and their prey in dry dipterocarp forests

Dry dipterocarp forest is a key dry forest type across South-East Asia. Despite these dipterocarps being endangered and widely unprotected, the factors that may affect their function at local and landscape scales are unknown. To identify drivers for future conservation programs at both local (habitat structure) and landscape (land use, climate) scales, the prey captured by web-building spiders, which are model predators in dry dipterocarps, were investigated. Overall, 21 dry dipterocarp forest stands representing the gradient of agricultural intensification were selected across North-East Thailand where captured and potential prey of web-building spiders was collected. Within each plot, the percentual coverage of major vegetation types (e.g., trees, shrubs, grass) was quantified. Around each plot, the landscape composition within a 5 km radius was quantified as the proportion of agroecosystems, forests, water bodies, and urban areas. Further, climate data for each plot were extracted from a public database. The prey captured by web-building spiders was most affected by the composition of landscapes; the evenness of captured prey showed a hump-shaped relationship with the proportion of agroecosystems in each landscape. The observed change in captured prey composition between plots was predominantly caused by changes in web type composition between local spider communities. The total number of captured prey decreased with increasing mean annual precipitation which mirrored the decline of total prey availability along this gradient. The results indicate that the predation by web-building spiders in dry dipterocarps is most threatened by changes in rainfall pattern and land-use change, specifically by agricultural intensification at the landscape scale.

DNA metabarcoding analysis of three material types to reveal Joro spider (Trichonephila clavata) trophic interactions and web capture

Introduced species alter established trophic interactions and molecular analysis can resolve changes in community structure and associated foraging links. Joro spiders (Trichonephila clavata) were recently introduced to the United States and their range is rapidly expanding across the east coast. Here, we used DNA metabarcoding of fecal samples, prey remains from webs, and dissected guts to compare diet composition of female Joro spiders in the southeastern United States. We amplified DNA from three material types using arthropod-targeted COI primers and sequenced with IIlumina MiSeq. Prey remains from webs had the highest diversity, richness, as well as the highest proportion of prey reads relative to Joro spider reads. Recovery of prey reads from fecal samples and dissected gut content was low and both were overwhelmed by Joro spider DNA. Although fecal samples and gut content had high proportions of Joro spider reads, fecal samples had higher prey diversity and richness. Moreover, we detected prey DNA from fecal samples several days after capture from the field, which reveals initial gut retention time estimates for fecal samples collected from web-building spiders. Combined, our results offer a first glimpse at the complexity of trophic associations for an introduced web-building spider and identify a viable material, prey remains from webs, as a source of prey DNA for estimates of biodiversity associated with web-building spiders.

Economic web-building behavior and behavioral investment trade-offs in a cobweb spider

Web-building spiders that build detritus-based bell-shaped cobwebs are model organisms for studies on behavioral plasticity because their web architecture components are easily quantified and behavioral investments are clearly separated. We investigated the web architectures and behavioral investments of the cobwebs built by Campanicola campanulata under different weight (heavy, medium, and light) detritus to research its cobweb architecture variation and analyzed the investment trade-off between foraging and defense. The results showed that spiders could actively choose lighter detritus to build retreats to reduce material and energy cost. There was a clear trade-off between defense and foraging investment of spiders choosing different weight detritus for their webs. The total length of gumfooted lines (foraging investment) was longer for the spiders that chose lighter detritus, but the energy expenditure during web-building (defense investment) was higher for the spiders that chose heavier detritus.

Climate Change, Extreme Temperatures and Sex-Related Responses in Spiders.

Climatic extremes, such as heat waves, are increasing in frequency, intensity and duration under anthropogenic climate change. These extreme events pose a great threat to many organisms, and especially ectotherms, which are susceptible to high temperatures. In nature, many ectotherms, such as insects, may seek cooler microclimates and 'ride out´ extreme temperatures, especially when these are transient and unpredictable. However, some ectotherms, such as web-building spiders, may be more prone to heat-related mortality than more motile organisms. Adult females in many spider families are sedentary and build webs in micro-habitats where they spend their entire lives. Under extreme heat, they may be limited in their ability to move vertically or horizontally to find cooler microhabitats. Males, on the other hand, are often nomadic, have broader spatial distributions, and thus might be better able to escape exposure to heat. However, life-history traits in spiders such as the relative body size of males and females and spatial ecology also vary across different taxonomic groups based on their phylogeny. This may make different species or families more or less susceptible to heat waves and exposure to very high temperatures. Selection to extreme temperatures may drive adaptive responses in female physiology, morphology or web site selection in species that build small or exposed webs. Male spiders may be better able to avoid heat-related stress than females by seeking refuge under objects such as bark or rocks with cooler microclimates. Here, we discuss these aspects in detail and propose research focusing on male and female spider behavior and reproduction across different taxa exposed to temperature extremes.

Subsidy Quality Affects Common Riparian Web-Building Spiders: Consequences of Aquatic Contamination and Food Resource.

Anthropogenic stressors can affect the emergence of aquatic insects. These insects link aquatic and adjacent terrestrial food webs, serving as high-quality subsidy to terrestrial consumers, such as spiders. While previous studies have demonstrated that changes in the emergence biomass and timing may propagate across ecosystem boundaries, the physiological consequences of altered subsidy quality for spiders are largely unknown. We used a model food chain to study the potential effects of subsidy quality: Tetragnatha spp. were exclusively fed with emergent Chironomus riparius cultured in the absence or presence of either copper (Cu), Bacillus thuringiensis var. israelensis (Bti), or a mixture of synthetic pesticides paired with two basal resources (Spirulina vs. TetraMin®) of differing quality in terms of fatty acid (FA) composition. Basal resources shaped the FA profile of chironomids, whereas their effect on the FA profile of spiders decreased, presumably due to the capacity of both chironomids and spiders to modify (dietary) FA. In contrast, aquatic contaminants had negligible effects on prey FA profiles but reduced the content of physiologically important polyunsaturated FAs, such as 20:4n-6 (arachidonic acid) and 20:5n-3 (eicosapentaenoic acid), in spiders by approximately 30% in Cu and Bti treatments. This may have contributed to the statistically significant decline (40%-50%) in spider growth. The observed effects in spiders are likely related to prey nutritional quality because biomass consumption by spiders was, because of our experimental design, constant. Analyses of additional parameters that describe the nutritional quality for consumers such as proteins, carbohydrates, and the retention of contaminants may shed further light on the underlying mechanisms. Our results highlight that aquatic contaminants can affect the physiology of riparian spiders, likely by altering subsidy quality, with potential implications for terrestrial food webs. Environ Toxicol Chem 2023;42:1346-1358. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

They mostly come at night: Predation on sleeping insects by introduced candy-striped spiders in North America.

They mostly come at night: Predation on sleeping insects by introduced candy-striped spiders in North America.