Spider Research Articles

Characterization of two full-length Araneus ventricosus major ampullate silk protein genes

Major ampullate silk is noted for its great tensile strength and extensibility. The impressive material properties of major ampullate silk result from their component proteins that encoded by members of the spidroin (spider fibroin) gene family. Although the major ampullate spidroin type has evolved multiple variants within specific-species, most sequences are fragmented. Here, we present two complete major ampullate spidroin genes from the orb-weaving spider Araneus ventricosus. Due to the abundant GPG motifs in their repetitive region, the two MaSp genes were grouped in MaSp2 subclass and named MaSp2C and MaSp2D, respectively. Analysis of the full-length gene sequences reveals that both of them include a single enormous exon (10,851 bp for MaSp2C and 8640 bp for MaSp2D) that mainly translates into a central repetitive region containing multiple amino acid motifs that can be organized into five ensemble types. We use gene-specific PCR primers to search the cDNA from major ampullate glands and find evidence for alternative splicing of MaSp2D transcripts into a minor spliceoform lacking the entire repetitive domain as well as the partial terminal regions. Our results not only provide new templates for protein-based materials with tailored properties, but suggest gene and transcriptional diversity of major ampullate silk.

Seven new records of bee flies (Bombyliidae, Diptera) from Saudi Arabia

BackgroundBombyliidae (bee flies) are one of the largest dipterous families in Saudi Arabia with 116 hitherto recorded species. Larvae of these flies are predators or parasitoids of different stages of other insects in the orders Orthoptera, Neuroptera, Coleoptera, Lepidoptera, Hymenoptera and Diptera, in addition to spiders (order Araneae, class Arachnida), so they have potential use as biological control agents for pests belonging to these orders.ResultsIn the present study, the list of Saudi Arabian fauna of bee flies (family Bombyliidae) is supplemented with seven new records in five genera and four subfamilies. The newly recorded species are Parageron lutescens (Bezzi, 1925) [Usiinae], Phthiria salmayensis Efflatoun, 1945 [Phthiriinae], Heterotropus bisglaucus Bezzi, 1925, Heterotropus maculiventris Bezzi, 1925, Heterotropus xanthothorax Efflatoun, 1945 [Heterotropinae], Anthrax greatheadi El-Hawagry, 1999, and Desmatoneura brevipennis (Bezzi, 1924) [Anthracinae]. World and local distributions of recorded species, diagnoses, remarks on feeding behaviors and some colored photographs were provided.ConclusionThe present study supplements the bee fly fauna (family Bombyliidae) in Saudi Arabia with seven new records. This brings the total number of bee fly species in the country into 123 species classified in 40 genera, 12 tribes and 10 subfamilies.

Revision of the new Australasian orb-weaving spider genus Salsa (Araneae, Araneidae).

A new Australasian genus in the orb-weaving spider family Araneidae Clerck, 1757 is described to include seven species: Salsafuliginata (L. Koch, 1871) comb. nov. (type species; = Epeirarubicundula Keyserling, 1887) syn. nov.) (Australia, introduced to New Zealand); S.brisbanae (L. Koch, 1867) comb. nov. (Australia); S.canalae (Berland, 1924) comb. nov. (New Caledonia); S.neneba sp. nov. (Papua New Guinea); S.recherchensis (Main, 1954) comb. nov. (Australia); S.rueda sp. nov. (Australia); and S.tartara sp. nov. (Australia; Lord Howe Island endemic). Salsa gen. nov. belongs to the Australasian informal backobourkiine clade and differs from other genera of this clade by a distinct abdominal shape (single posterior abdominal tubercle) and ventral colouration (pale lateral spindle-shaped bands), male pedipalp morphology (C-shaped median apophysis that has teeth-like tubercles inside the basal arch) and the shape of the female epigyne scape (partially translucent and generally shorter than the epigyne plate). Based mainly on male pedipalp morphology within the backobourkiines, Salsa gen. nov. has closest morphological affinities with Acroaspis Karsch, 1878 and Socca Framenau, Castanheira & Vink, 2022.

Population ecology of the orb-weaver spider Eustala taquara (Keyserling) (Araneidae)

ABSTRACT The density and age structure of spider populations are affected by biotic and abiotic factors. The orb-web spider Eustala taquara (Araneidae) lives camouflaged on the dead vegetation of shrubs, especially in forest edges. Here, we describe the variation in the number of individuals over the year and the phenology of a population of E. taquara. We also tested whether these variables are influenced by temperature, precipitation or prey availability. We conducted the research in a tropical rainforest located in south-eastern Brazil. We recorded the number of spiders and their development stages (spiderling, young, juvenile, sub-adult and adult) monthly, for two years, along 1 km at the forest edge at an altitude of 1000 m above sea level. We estimated prey availability using 20 circular transparent plates containing tanglefoot on one side, exposed for 48 hours in the vegetation, sampled monthly for 18 months. We used circular statistics to assess the peaks of individuals during the study period, verifying the occurrence of time lags between the number of spiders with the climatic variables and prey availability. The population of E. taquara increased in periods of lower precipitation and temperature, and decreased during the rainy season. Thus, the population showed a negative correlation with the climatic variables and potential prey availability. All instars were present simultaneously, revealing that spiders can reproduce at any time of year. During the dry season, the higher number of spiders may be related to the increase in branches and dead plants that provide camouflage against visually oriented predators and sites for web building, increasing the likelihood of obtaining food.

A new genus of Australian orb-weaving spider with extreme sexual size dimorphism (Araneae, Araneidae)

The new Australian orb-weaving spider genusMangroviain the family Araneidae Clerck, 1757 is described. It is characterised by extreme sexual size-dimorphism (eSSD) with females (total length 8–10 mm) ca. 3 to 5 times larger than males (2.5–3 mm). WhilstMangroviashares with the informal Australian ‘backobourkiine’ clade a single seta on the male pedipalp patella, the genus is probably more closely related to the ‘zealaraneines’ or associated genera. In addition to eSSD and the single patellar spine, the genus is characterised by a distinct subterminal embolus branch in males. The new genus includes two species: the type speciesMangrovia albida(L. Koch, 1871)comb. nov.(=Epeira fastidiosaKeyserling, 1887,new syn.) from Queensland andMangrovia occidentalissp. nov.from Western Australia. Both species are apparently coastal and occur in mangroves, but also in riparian woodland. Spiders were found resting in rolled-up leaves adjacent to their orb-web.

THE FIRST RECORD OF THE GENUS $ARGIOPE$ OF THE FAMILY ARANEIDAE: $ARGIOPE$ $BRUENNICHI$ (SCOPOLI, 1772) AND $ARGIOPE$ $LOBATA$ (PALLAS, 1772) IN ARMENIA

The article presents the first record of the genus Argiope, orb-weaver spiders from the Araneidae family in Armenia. The two female specimens of Argiope bruennichi (Scopoli, 1772) were found in the Lori Region (northern part), and two specimens of the female spider of Argiope lobata (Pallas, 1772) were recorded in the Tavush Region (north-eastern part) and Armavir Region (south-western part) of Armenia in 2020–2022.

The Use of Tuning Forks for Studying Behavioural Responses in Orb Web Spiders

Simple SummarySpiders are common predators found in almost every type of environment, and are used as model organisms in studies ranging from communication and signalling to biochemical studies on their silk. Orb spiders are particularly interesting, as their web provides a cost-effective way to obtain information on their foraging behaviour. However, studies on short-term behaviours including prey capture and escape behaviours are rare and usually take place in artificial settings, such as laboratories. In this study, we tested a simple methodology using tuning forks that can be used consistently and reliably in the field. The two tuning forks are capable of producing attack (440 Hz) and escape (256 Hz) responses from the spiders. We also used a metal wire as a mechanical stimulus for comparison, which as predicted, was less reliable. We demonstrate the usefulness of the methodology by quantitatively investigating how the size of the spider and the size of its web affect predatory and escape response rates in the autumn spider, although no significant effects of either were found. However, our results confirm the ease by which this simple method can be used to conduct behavioural studies of orb spiders in the wild.Spiders and their webs are often used as model organisms to study a wide range of behaviours. However, these behavioural studies are often carried out in the laboratory, and the few field studies usually result in large amounts of video footage and subsequent labour-intensive data analysis. Thus, we aimed to devise a cost- and time-effective method for studying the behaviour of spiders in the field, using the now almost forgotten method of stimulating webs with tuning forks. Our study looked at the viability of using 256 Hz and 440 Hz tuning forks to stimulate, anti-predatory and predatory responses in the orb web spider Metellina segmentata, respectively. To assess the consistency of the behaviours produced, we compared these to direct mechanical stimulation with a metal wire. The results suggest that the tuning forks produce relatively consistent behaviours within and between two years in contrast to the metal wire. We furthermore found no significant effects of spider length or web area on spider reaction times. However, we found significant differences in reaction times between escape and prey capture behaviours, and between tuning forks and the wire. Thus, we demonstrated the potential of tuning forks to rapidly generate quantitative data in a field setting.

Male spiders avoid sexual cannibalism with a catapult mechanism

In the animal world, numerous mechanisms have been described that allow for extremely fast actions or reactions via the slow storage of energy, typically in elastic structures, which is then nearly instantly released1-4, similar to the operation of a catapult. Many of these mechanisms are employed for prey capture1,2 or for predator avoidance3,4; however, such superfast actions have not yet been reported as a means to dodge sexual cannibalism. Here, we unveil a novel mechanism in a communal orb-weaving spider Philoponella prominens (Uloboridae) (Figure S1), whereby males undertake a split-second catapult action immediately after mating, thereby fleeing their partner (Video S1). We demonstrate that males achieve their superfast action (up to 88.2 cm/s) by extending the tibia-metatarsus joint of their first leg pair via hydraulic pressure in a joint that is known to lack extensor muscles in spiders. This rapid expansion greatly reduces the likelihood of the male being sexually cannibalized.

Outsourced hearing in an orb-weaving spider that uses its web as an auditory sensor

SignificanceThe sense of hearing in all known animals relies on possessing auditory organs that are made up of cellular tissues and constrained by body sizes. We show that hearing in the orb-weaving spider is functionally outsourced to its extended phenotype, the proteinaceous self-manufactured web, and hence processes behavioral controllability. This finding opens new perspectives on animal extended cognition and hearing-the outsourcing and supersizing of auditory function in spiders. This study calls for reinvestigation of the remarkable evolutionary ecology and sensory ecology in spiders-one of the oldest land animals. The sensory modality of outsourced hearing provides a unique model for studying extended and regenerative sensing and presents new design features for inspiring novel acoustic flow detectors.

Observation: Setting the Foundation for Creativity and Innovation.

Observation: Setting the Foundation for Creativity and Innovation.

Sentinel Riparian Spiders Predict Mercury Contamination of Riverine Fish.

Mercury (Hg) is a widespread and toxic environmental contaminant. It is challenging to determine the level of Hg contamination of food chains and fish within the millions of water bodies in the United States. Mercury contamination can vary 10-fold between ecosystems, even those in the same region. Therefore, aquatic ecosystems need to be individually monitored for Hg contamination to determine which ecosystems are most contaminated and pose the greatest risk to human and wildlife health. One approach to monitoring Hg is to use sentinel species, defined as biological monitors that accumulate a contaminant in their tissues without significant adverse effects. Riparian spiders such as long-jawed orb weavers (Tetragnathidae) have been proposed as sentinels of persistent bioavailable contaminants, like Hg, in aquatic systems. Long-jawed orb weavers feed on emergent aquatic insects and have concentrations of Hg that reflect levels of Hg contamination in the aquatic food web. Previous studies have documented elevated contaminant concentrations in long-jawed orb weavers from shorelines of aquatic ecosystems, suggesting that they could be used as sentinels of chemical contaminants in aquatic ecosystems. We demonstrate for the first time that long-jawed orb weavers can be used as sentinels to identify aquatic systems that contain fish with elevated concentrations of Hg.Environ Toxicol Chem 2022;41:1297-1303. © 2022 SETAC.

Stabilized Morphological Evolution of Spiders Despite Mosaic Changes in Foraging Ecology.

A prominent question in animal research is how the evolution of morphology and ecology interacts in the generation of phenotypic diversity. Spiders are some of the most abundant arthropod predators in terrestrial ecosystems and exhibit a diversity of foraging styles. It remains unclear how spider body size and proportions relate to foraging style, and if the use of webs as prey capture devices correlates with changes in body characteristics. Here, we present the most extensive data set to date of morphometric and ecological traits in spiders. We used this data set to estimate the change in spider body sizes and shapes over deep time and to test if and how spider phenotypes are correlated with their behavioral ecology. We found that phylogenetic variation of most traits best fitted an Ornstein-Uhlenbeck model, which is a model of stabilizing selection. A prominent exception was body length, whose evolutionary dynamics were best explained with a Brownian Motion (free trait diffusion) model. This was most expressed in the araneoid clade (ecribellate orb-weaving spiders and allies) that showed bimodal trends toward either miniaturization or gigantism. Only few traits differed significantly between ecological guilds, most prominently leg length and thickness, and although a multivariate framework found general differences in traits among ecological guilds, it was not possible to unequivocally associate a set of morphometric traits with the relative ecological mode. Long, thin legs have often evolved with aerial webs and a hanging (suspended) locomotion style, but this trend is not general. Eye size and fang length did not differ between ecological guilds, rejecting the hypothesis that webs reduce the need for visual cue recognition and prey immobilization. For the inference of the ecology of species with unknown behaviors, we propose not to use morphometric traits, but rather consult (micro-)morphological characters, such as the presence of certain podal structures. These results suggest that, in contrast to insects, the evolution of body proportions in spiders is unusually stabilized and ecological adaptations are dominantly realized by behavioral traits and extended phenotypes in this group of predators. This work demonstrates the power of combining recent advances in phylogenomics with trait-based approaches to better understand global functional diversity patterns through space and time. [Animal architecture; Arachnida; Araneae; extended phenotype; functional traits; macroevolution; stabilizing selection.].

Together but not intertwined: differences in sexual behavior between two sympatric and synchronic spider species, including one new synonymy (Araneae: Tetragnathidae: Tetragnatha)

Species recognition and reproductive isolation are critical for organisms to prevent expensive and unsuccessful matings. This may be particularly important in closely related species that coexist synchronously in the same habitat, and for which reproductive barriers are not entirely effective. Tetragnatha argentinensis Mello-Leitão, 1931 and T. nitens (Audouin, 1826) are two long-jawed orb weaver spiders whose feeding grounds and reproductive phenology overlap extensively. Since general patterns of sexual behavior observed in the field showed no apparent differences between these two species, we proposed to evaluate the occurrence of heterospecific mating, and explored the occurrence of potential reproductive isolation mechanisms between them by analyzing in fine scale the mating behaviors of each species and sex. We observed only one heterospecific mating, and few or no sexual interactions occurred in other crossed trials. We found that both species showed similar general mating patterns, however, there are some subtle differences between them. In T. nitens, males clasped the female's chelicerae with their own, but the opposite occurred in T. argentinensis. Moreover, males of T. nitens produced fewer hematodochal inflations, lower number of flubs, and shorter insertions than males of T. argentinensis. Females of T. argentinensis vibrated their abdomen at a higher rate. Our results indicate that these sympatric Tetragnatha species have successful reproductive isolation that probably takes place through recognition mechanisms occurring prior to mating. We provide an update on the taxonomic status of T. argentinensis and its distribution, and a new junior synonymy.

Search image formation for spider prey in a mud dauber wasp.

Search images are perceptual biases acquired through experience that improve an individual’s ability to detect the object of their search (e.g., a predator seeking prey). In hymenopterans, examples include floral search images in bees and acquired sensory biases towards specific prey in wasp predators. Mud dauber wasps exhibit individual specialization and consistency in prey preferences through time, often based on visual and chemical cues, that may vary at intraspecific levels. However, the search image concept in wasps has not been evaluated from a visual ecology perspective. Using psychophysical visual modelling from multispectral digital photography, we measured the colour and body pattern of the spiders captured and stored in nests by the wasp Trypoxylon mexicanum. Those visual traits were compared at the community and nest cell levels, according to the nest provisioning sequence, and its relationship with spider diversity. Our results show that the wasps are choosing a small group of orb weavers (Araneidae) with similar coloration and body patterns. These findings highlight the specific visual features that may be the focal trait during search image formation in these wasps. The colour and pattern variables of spider prey were consistent over time, suggesting that individual search images may strengthen with experience.

Determination of the prey impact region in a spider orb-web from in-plane vibration

In this paper we study the inverse problem of locating a prey in a spider orb-web from measurements of the in-plane dynamic response of the web immediately after the impact. The orb-web, having axial symmetry and fixed boundary, is described by a continuous pre-stressed membrane undergoing infinitesimal deformation. The impact of the prey is modeled by an in-plane pressure field, whose two spatial components constitute the unknowns of the inverse problem. A reconstruction algorithm for the impact region is proposed, which is essentially based on the determination of certain generalized Fourier coefficients of the loading terms starting from discrete in-plane dynamical measurements that mimic what the spider performs in nature. The results show that the information gathered by the spider positioned at the center of the web is sufficient for a precise localization of the prey, for different prey and orb-web characteristics. The simulations also show that the sensitivity of the reconstruction to errors on the data is significant only when the observation time is close to the theoretical minimum time.

Arthropods associated to tree canopies in the edges of a forest fragment in the Cerrado of Minas Gerais, Brazil

The Cerrado biome occupies 22% of Brazil's land area and has one of the highest levels of endemism of flora and fauna species of any biome. As components of the fauna, the arthropods stand out as they perform several functions within ecosystems and serve as bioindicators of environmental quality. This work aimed to evaluate the association of the arthropod fauna with tree canopies in an area surrounding a fragment of a legal reserve adjacent to a coffee plantation. The study was conducted at the Juliana farm (18°43'29"S; 47°29'55"W), located in the municipality of Monte Carmelo, Minas Gerais, Brazil. The canopy net methodology was used, in which a net bag was wrapped around the branches and shaken five times, covering the four cardinal directions in the crowns of 20 trees. The contents of the net were placed in plastic bags, sealed, identified, and taken to the laboratory. Twelve monthly collections were performed between August 2018 and July 2019, for a total of 240 samples. The collected specimens were identified in taxonomic groups using a taxonomic key. During the sampling period, 804 individuals were collected, belonging to 56 taxa of the classes Arachnida and Insecta. Xylopia aromatica (Annonaceae) was the most representative tree species, with 50% of the sampled taxa found in its branches. The order Araneae and the families Asilidae and Tephritidae (Diptera) and Formicidae (Hymenoptera) were the predominant taxa in the faunistic analysis. As potential predators, Araneae and Formicidae were the most important groups and were found in all tree species sampled. The families Braconidae and Ichneumonidae (Hymenoptera) were the most common among the parasitoids. We conclude that the legal reserve and permanent preservation areas maintain populations of tree species that can generate a survival site for natural enemies and other canopy arthropods.

Web building behavior in a wall spider (Oecobiidae) suggests a close relationship with orb-weavers

Behavior is often phylogenetically informative and detailed descriptions of behavior have been used to support taxonomic relationships in several groups, such as birds, lizards, and arthropods. Web building behavior has provided informative traits to several spider families, but observations are lacking for other families, such as wall spiders Oecobiidae. Recent phylogenetic hypotheses based on molecular traits placed oecobiids either close to cribellate orb weavers (Uloboridae) or to long-spinneret spiders (Hersiliidae). Here, we describe for first time the web construction behavior and details of the web design in the oecobiid Oecobius concinnus Simon 1893 (Oecobiidae). We compare them with uloborid and araneoid orb weavers. If Oecobiidae and Uloboridae are closely related, we expect that O. concinnus share some web construction behaviors with these orb weavers. Video recordings and analyses of web structures suggest the sequence of web construction (radii, then sticky spiral construction) and the arrangement of cribellate threads are possible homologies between Oecobiidae and orb weavers, supporting a close relationship of Oecobiidae with Uloboridae.

Slit sense organ distribution on the legs of two species of orb-weaving spider (Araneae: Araneidae)

Biotic and abiotic mechanical stimuli are ubiquitous in the environment, and are a widely used source of sensory information in arthropods. Spiders sense mechanical stimuli using hundreds of slit sense organs (small isolated slits, large isolated slits, groups of slits and lyriform organs) distributed across their bodies and appendages. These slit sense organs are embedded in the exoskeleton and detect cuticular strain. Therefore, the spatial pattern of these sensors can give clues into how mechanical stimuli from different sources might be processed and filtered as they are transmitted through the body. Here, we map the distribution of slit sense organs on the legs in two species of orb-weaving spider, A. diadematus and T. edulis, in which slit sense organ distribution has not previously been investigated. We image the spiders’ legs using scanning electron microscopy, and trace the position and orientation of slits on these images to describe the distribution and external morphology of the slit sense organs. We show that both species have a similar distribution of slit sense organs, with small isolated slits occurring in consistent lines parallel to the long axis of the legs, whilst large isolated slits, groups of slits and lyriform organs appear in fixed positions near the leg joints. Our findings support what has been described in the literature for several other species of spider, which indicates that slit organ arrangement is conserved across spiders in different evolutionary lineages and with disparate hunting strategies. The dispersed distribution of small isolated slits along the whole length of the leg may be used to detect large-scale strain of the leg segment as a result of muscle activity or internal changes in haemolymph pressure.

Long spider bodies under the sun

Spiders are underrated. We tend to think of them as creepy crawly cellar dwellers or as Halloween decor, but there is a lot more to spiders than that. Rather than hiding out in dark crevices, many spend their days fully exposed on their webs, enduring heavy rain, howling wind or bright sunlight. Spiders also come in a huge variety of shapes: some have very round, ball-like abdomens, whereas others have an elongated or cylindrical back end. With all this diversity in lifestyle and form, it's not surprising that spiders thrive in every terrestrial habitat, often with the aid of curious adaptations to the peculiarities of their home turf. Interested in the many ways that spiders live their lives and how they cope with environmental challenges, Leonardo Ferreira-Souza from the University of Brasilia, Brazil, and colleagues investigated how a spider's daily dose of sunlight shapes its body.Ferreira-Souza and colleagues hypothesized that elongated abdomens were more common in spiders routinely exposed to the sun and that this feature protected them from overheating, as some spiders point the end of their abdomen towards heat sources such as the sun. For example, if a spider's abdomen is cylindrical, then this unusual posture could keep most of their body surface out of direct sunlight and help them stay cool. To test their idea, the team scoured museum and scientific archives for photos and illustrations of orb spiders – the most common spiral web-spinning spiders – from the Caribbean, Central America and South America, measuring the total area and roundness of as many spider abdomens as possible. They also classified each spider as either sun exposed or sun protected, where sun-exposed spiders were active during the day, typically soaking up the rays sitting on their webs, while sun-protected spiders were active at night or spent their waking daytime hours in shelters such as leaf litter.Thousands of measurements later, it was clear that the sun-exposed spiders had more cylindrical body shapes on average than sun-protected spiders. The scientists then turned their attention to the physiological implications of the spiders’ abdomen shapes, calculating how warm different shaped arachnids would get under natural conditions. They paid special attention to how often their simulated spiders exceeded two key temperatures: 35°C, a temperature that most spiders avoid, and 40°C, a temperature where many spiders show symptoms of overheating such as leg spasms or slipping into a coma. If the elongated body shape was adaptive for heat management, then cylinder-shaped spiders should be less likely to reach dangerously hot body temperatures.As predicted, the cylinder-shaped spiders stayed cool. On a typical 30°C day, the body temperature of an elongated spider would only reach 33°C, whereas a round spider of the same size would hit a dangerous 40°C. By plugging in 10 years’ worth of historical weather data, the researchers estimated that the round spider would experience 85 days per year at or above an uncomfortable 35°C, including 8 days when its body temperature would be critical at 40°C. In contrast, the simulated elongated spider had much fewer heat stress days, only reaching a body temperature above 35°C for 36 days per year and never experiencing a body temperature above 40°C.Like many animals, spiders have adapted their bodies to survive the challenges of their habitat. Unlike many animals, at least unlike many vertebrates, spiders have literally changed the shape of their bodies as a thermoregulatory strategy, stretching out their abdomens over evolutionary time to protect themselves from overheating. Spiders are way cooler than we give them credit for!

Phylogenetic evidence for an independent origin of extreme sexual size dimorphism in a genus of araneid spiders (Araneae: Araneidae)

Cyphalonotus is a poorly studied Old World araneid spider genus of which the phylogenetic proximity remains unknown due to the paucity of morphological and molecular data. We test the phylogenetic placement and the taxonomic composition of Cyphalonotus and place the male and female size variation of Cyphalonotus and related genera in an evolutionary context. Our collection and field observations from Taiwan and China facilitate description of a new and a known species, and original sequence data enable species delimitation and phylogenetic analyses. The phylogenetic results reject all four classification hypotheses from the literature and instead recover a well-supported clade comprising Cyphalonotus + Poltys. We review the male and female size variation in Cyphalonotus, Poltys and related genera. These data reveal that all known species of Poltys are extremely sexually size dimorphic (eSSD = females over twice the size of males) reaching values exceeding 10-fold differences, whereas Cyphalonotus and other genera in phylogenetic proximity are relatively sexually monomorphic (SSD < 2.0). This confirms an independent origin of eSSD in Poltys, one of multiple convergent evolutionary outcomes in orbweb spiders.