The interaction of polysphinctine ectoparasitoids with their 2D-web-building spider hosts is characterized by alterations in web-building behavior, where the manipulated spider builds a so-called “cocoon web”, a unique structure that is important for pupal survival. Alteration of the web architecture of spider hosts building a 3D web has been observed only rarely. We documented interactions between the parasitoid Acrodactyla degener and the linyphiid sheet-web-building spider Mughiphantes mughi (Fickert, 1875), a new host from spruce stands in central Europe. When the parasitoid reached the final instar larva, the spider was killed and consumed on the underside of the sheet web (the typical spider position on the sheet web), after which the parasitoid larva produced a cocoon incorporated horizontally into the sheet of the web. We identified the reduction of some parts of the web of parasitized M. mughi, but the origin and the function of this reduction are not clear.

Adult female spiders of the brown widow spider, Latrodectus geometricus CL Koch, 1841, lay multiple egg sacs during their lifetime, with each egg sac containing between 50 and 250 offspring. The mother supplements her developing embryos with additional lipids and proteins, and the spiderlings undergo one molt within the egg sac before emerging. Thereafter, the spiderlings may remain in the mother's web for up to several days, and then disperse and build their own webs and seek prey. Prey availability, however, is unpredictable, and may differ among habitats. For synanthropic spiders like L. geometricus, that live in close proximity with human dwellings, prey availability might vary considerably. Here, we compared mortality, growth and development of the brown widow spider, Latrodectus geometricus, from neonate to adult under two different prey availability regimes. Growth curves were plotted by weighing spiderlings fed weekly or every three weeks on fruit flies and then blow flies or crickets. Mortality rates were significantly higher when spiderlings received less prey, and only 7 spiderlings survived when fed intermittently, whereas of those fed weekly, approximately 60% reached adulthood. Males developed linearly, molted a mean of approximately 4 times, and attained maximum body masses after ∼100 days, whereas females developed exponentially, molted 8-9 times, and reached maximum body masses after ∼170 days. The growth rate of males was consistent across different instars whereas it was highest in later female instars. Mature males were less than 1% as large as mature females, revealing extreme sexual size dimorphism in this species.

Biofluorescence has been reported in all extant chelicerate orders, but genus- or species-specific documentation remains limited. This gap is particularly noticeable in amblypygids (tailless whip spiders), where detailed descriptions of biofluorescence have not yet been fully developed. Here, we present the first description and photographic documentation of suspected biofluorescent patterns in Mesoamerican amblypygids. We collected two specimens, likely belonging to the genera Paraphrynus Moreno, 1940 and Phrynus Lamark, 1801, from an urban area on the Pacific coast of Guanacaste, Costa Rica. Under 365 nm light, these specimens appeared to display blue-green fluorescence at the joints and soft cuticle segments. Our findings suggest that further research is necessary to confirm the presence of fluorophores by using techniques such as spectrofluorimetry, to explore the ecological role of biofluorescence, and to describe biofluorescent patterns across amblypygid taxa. 

Polysphinctine wasps have evolved highly specialized life strategies that allow them to parasitize different spider hosts effectively. In this report, we document juvenile orchard orb-weavers Leucauge tessellata (Thorell, 1887) singly carrying larvae of a polysphinctine wasp from the Acrodactyla quadrisculpta-group. The wasp was identified using its morphological characteristics, mode of parasitism, and mt-COI phylogenetic analysis. Observations revealed that all three Acrodactyla sp. larvae collected were attached to the left mediolateral abdomen of the host spiders, where they consumed hemolymph until pupation. Before being killed by their parasitoids, host spiders exhibited modified web-building behavior, constructing a reduced cocoon web in place of the characteristic orb web of L. tessellata. Our PLS-PM analysis showed a significant negative correlation between the host spider's developmental stage and the parasitism rate (P = 0.02), which suggests that Acrodactyla sp. wasps selectively target juvenile L. tessellata, likely because they are less able to dislodge the larva from its attachment site compared to adult spiders. We speculate that the apparently consistent site of larval attachment in this specific spider-parasitoid interaction may represent a specific host-utilization adaptation in the observed Acrodactyla sp. wasps. Further investigation is warranted to strengthen evidence for our interpretation of this behavior and to explore its evolutionary implications.

Scorpions mainly feed on insects and other invertebrates. However, several species include small vertebrates in their diets. Here, we report a case of lizard consumption by a Mediterranean scorpion. This is the first documented case of Aegaeobuthus gibbosus (Brullé, 1832) (Buthidae) preying on the gecko Mediodactylus kotschyi, adding to a limited body of reports of lizard predation by European scorpions.

Courtship and mating behaviors are conspicuous and can attract eavesdroppers that pose a threat to both males and females. The body condition of females has significant effects on their reproductive output and so males should value well-fed females and be willing to take on increased risk in exchange for the opportunity to mate. We tested the hypothesis that predation risk affects male activity and mating behavior differently based on the female's body condition. We manipulated the body condition of female Pardosa milvina (Hentz, 1944) (Araneae: Lycosidae) and monitored the activity of males when placed on female substrate–borne cues with or without similar cues from their common predator, Tigrosa helluo (Walckenaer, 1837) (Araneae: Lycosidae). Males appeared to engage in a search for females on cues from well-fed females as they spent more time walking but covered less distance. Predator cues reduced this activity when coupled with cues from well-fed, but not food-limited females. In a second experiment, males were paired with females that differed in body condition and included treatments with and without predator risk. Females in good condition attacked males less and were more likely to mate. Males courted hungry females longer, but with the same intensity as well-fed females. Predation risk eliminated aggression toward males by well-fed females. In summary, males were able to identify the body condition of prospective mates from chemotactile cues alone, but when females were present, predation risk had little impact on the aspects of courtship and mating that we documented.

This investigation identifies arachnid prey of juvenile salmonid fishes (Oncorhynchus spp.) in a coastal stream in Marin County, California. Using morphological identification and DNA sequencing of the metazoan barcode gene (cytochrome c oxidase subunit I), arachnids recovered from salmon gut lavage samples were identified. The non-invasive specimen-specific sequencing approach allows for an association of the specimen with sequence data, something often lacking in metabarcoding or eDNA studies. To identify potential source habitats, the guilds of the spiders and mites studied were classified. No samples were contaminated, and genus-level identifications were achieved in all spiders, with species-level identifications in 38% of spiders. These findings provide insight into the arachnid prey within aquatic ecosystems, aiding our understanding of allochthonous contributions to freshwater environments and their fish predators. These contributions have implications for ecosystem dynamics, nutrient cycling, contaminant accumulation, and conservation broadly. 

The efficacy of spider orb webs depends on the functional integration of architecture and material properties. Here, we investigated species-specific correlations between orb web architecture and mechanical properties of major ampullate silk (i.e., radii silk) across several orb-weaving spider species. To disentangle the effect that manipulation during the spinning process and the composition of major ampullate silk have on this relationship, the silks were tested in two states. In the native state, the spider tailors the mechanical properties of the radii silks to their intended function within the constraints provided by the silk's composition. In contrast, in the freely supercontracted state after exposure to high humidity, much behavioral manipulation is removed, revealing the silk's intrinsic material properties conveyed by its primary structure. While the properties of freely supercontracted silk are not directly relevant to web function, combining this information with native silk data generated a more complete picture of the underlying processes of silk adaptation. While the number of spiral turns was positively correlated with native silk extensibility, supercontracted silk strength and toughness were positively correlated with the number of radial threads in a web. These results suggested a concerted use of intrinsic and behaviorally manipulated silk properties and web architecture to maximize web performance. Thereby, different silk properties are adjusted via alternative routes, possibly due to the specific energetic cost associated with each adjustment.

Spiders of the genus Actinopus Perty, 1833 are known to engage in ballooning, but this behavior has never been observed in the field. Here, we report and describe the observation of pre-ballooning behaviors by Actinopus juveniles in nature, including the use of a silk platform for ballooning take-off. Ten individuals were also collected and observed for ballooning behaviors in laboratory conditions. Both in nature and in the laboratory, individuals exhibited behaviors such as raising their legs and spinnerets, possibly to facilitate the perception of mechanical signals such as air currents. The pre-ballooning silk platform was observed in an area devoid of bushes and trees, which suggests that the spiders may have built this platform to compensate for a lack of vertical structures in the vicinity. 

The ability to adhere to surfaces is particularly relevant for cursorial predatory arthropods like hunting spiders, which often traverse relatively complex environments characterized by large variation in substrate properties. Here, we evaluated the adhesive performance of six hunting spider species that are common in eastern temperate North America and lack specialized tarsi for climbing smooth or inclined surfaces [Lycosidae: Pardosa lapidicina Emerton, 1885 and Rabidosa rabida (Walckenaer, 1837); Oxyopidae: Oxyopes salticus Hentz, 1845; Pisauridae: Pisaurina mira (Walckenaer, 1837); Dolomedidae: Dolomedes triton (Walckenaer, 1837), and Dolomedes scriptus Hentz, 1845]. We tested adhesion performance as shear load resistance (g) on a glass plate, and as the angle of failure (°) when the plate was gradually inclined relative to horizontal. Average angle of failure and shear resistance differed among species, and shear resistance increased interspecifically with mass. Rabidosa rabida had the highest average angle of failure and shear resistance. Adhesive performance was not related to tarsal index (tarsal contact area per unit mass) for most species, but shear resistance declined with increasing tarsal index in Pardosa lapidicina and Rabidosa rabida. Collectively, these results suggest that, for spiders lacking specialized adhesive tarsi, adhesive performance is largely a function of basic physics, i.e., the interaction of mass and contact area with a substrate.
Supplemental Materials
Figure S1.—Images of the second foot (Labarque et al. 2017) of each of the six focal species. Figure S2.—Image of the second foot of Pardosa lapidicina showing the tracing method used to estimate contact area. Figure S3.—Diagram of angle of failure tests with the spider facing at an upward angle and downward angle. Table S1.—The distribution of individuals among species and sex in the two experiments. Table S2.—Statistical results for the full model. Shear load data were log-transformed before analysis. Table S3.—Medians and ranges for spider parameters and adhesive performance variables measured. Table S4.—Species-specific regression results for shear load and angle of failure vs. tarsal index. - Download file

Insecticides are commonly used to mitigate damage caused to crops by numerous insect pests. These chemicals can
have reverberating impacts on nontarget species, including beneficial species such as orb-weaving spiders (Araneae: Aranaeidae). Orb-weavers provide natural pest control services, but even subtle, sublethal effects of insecticide residues may alter the provisioning of such services, including changes in web building and predatory behaviors. We examined the effects of a low concentration of the commercially available insecticide Talstar®, which contains the synthetic pyrethroid bifenthrin, on survival, web-building frequency, and web architecture of the banded garden spider, Argiope trifasciata (Forsska°l, 1775). Exposure to Talstar® significantly reduced survival and web building propensity: after four days 60% of the treatment group were still alive (vs. 93% of the control) and only 42% of surviving spiders of the treatment group built webs (vs. 61% of the control). Hence, bifenthrin had a negative effect on web building behavior and survival, even at a supposedly sublethal dose (0.22 mL/L Talstar®, corresponding to 0.0174 mL/L a.i.). These results indicate that even exposure to a very low residual concentration
Supplemental Materials
Table S1.—Number of surviving individuals, number of individuals with web, and percentage of individuals with web (of surviving spiders) for the first four days post exposure. Table S2.—The best predictive model explaining the probability of web presence during the first four days post exposure based on the full model containing cephalothorax width and condition, as well as the corresponding interaction terms with treatment, but not the treatment x days since exposure interaction. - Download file

We developed a monoclonal antibody (MAb) to Platynota stultana (Tortricidae, common name omnivorous leafroller), a key pest of grape in California, and used it to detect predation by spiders in San Joaquin Valley vineyards. Using an enzyme-lined immunosorbant assay, we found a MAb with high specificity to P. stultana, with no cross reaction to several non-lepidopteran insects, and minor reaction to other lepidopteran species. We tested the MAb on four spiders: Cheiracanthium inclusum (Hentz, 1847) (Cheiracanthiidae), Trachelas pacificus Chamberlin & Ivie, 1935 (Trachelidae), Oxyopes spp. (Oxyopidae) and Hololena nedra Chamberlin & Ivie, 1942 (Agelenidae), and found for all but C. inclusum, there was reactivity to spiders which had eaten P. stultana larvae in the laboratory. We sampled spiders from two Fresno County vineyards, assaying by species and weight at antigen dilutions of 1:100 and 1:1000. None of the small-sized Oxyopes spp. or H. nedra specimens was positive, but 8.8% of the medium-sized Oxyopes spp. and 33.3% of the medium- and large-sized H. nedra specimens were. 28.5% of the small-, 57.1% of the medium- and 66.6% of the large-sized T. pacificus specimens tested positive. Our interpretation is that the H. nedra positives resulted from P. stultana moth capture, and that Oxyopes spp. prey upon P. stultana larvae, but have a limited ability to capture them. Trachelas pacificus appears to be an effective predator of immature P. stultana, capable of finding and consuming those hidden in their nests, and may play a positive role in lowering its population density.

A new troglobitic species belonging to the genus Paratricommatus Piza, 1943 (Cryptogeobiidae), was found in a cave in the Pains municipality, Minas Gerais state, Brazil, and is described here. Paratricommatus infernalis sp. nov. is distinguished from all other species in the genus by having the IV femur 1.5–2.5 longer than the dorsal shield (instead of the IV femur shorter than the dorsal shield) and small eyes with reduced pigmentation. This new species presents several troglomorphic traits, such as elongated legs and different degrees of reduction in integumentary and ocular pigmentation, in addition to being absent in epigean environments. Thus, it is considered a troglobitic species and may represent a relic, as evidenced by its geographic isolation from other Cryptogeobiidae species.

In the present study, the reproductive behavior of a representative of the Deinopidae family, Deinopis cf. cylindracea C. L. Koch, 1846, is described for the first time. The behavioral aspects observed were the construction of the male's sperm web, male's approach to fertilization, and end of the couple's pairing. As soon as a male found a female, he began sperm induction. The sperm web is a Y-shaped web, whose internal space forms a flat surface onto which the male deposits his gametes. Sperm were then collected by his copulatory bulbs from the opposite side of the web. After transferring the sperm drops to the pedipalp, the male walked towards the female, approaching her from the dorsal-abdominal region using the dragline thread of the web. The male used his legs to touch both the web and female spider, inducing the female to let go, and positioned her ventral region towards his cephalothorax. The couple hung upside down; the female was suspended by a thread, her cephalothorax perpendicular to the floor. In this position, the male inserted the embolus of the copulatory bulb into the female epigynum and transferred the sperm. The male separated quickly by extending his legs and moving away, returning to an uppermost position in relation to the female. The female, in turn, returned to the prey-ready posture, clipping the capture net again and positioning herself in the same manner as before the reproductive behavior.

The intraspecific diversity of the few mygalomorph spiders in southern Appalachia has received considerable attention, revealing highly localized and deeply divergent populations and in some cases cryptic species. The araneomorph fauna of the region has received comparatively little study, due to its higher diversity, more tentative taxonomy, and perhaps perception that short-range endemicity might be lower. In this study, we examined this last assumption, surveying patterns of intraspecific diversity across Araneomorphae occurring in the leaf litter of high elevation spruce-fir sky islands of southern Appalachia, as revealed by population level metabarcoding. In most species, intraspecific haplotypic diversity, while high, revealed little geographic pattern, generally supporting assumptions of low regional endemicity. Of 50 spider species found in spruce-fir forest litter, more than 30 occur more widely, and showed little sign of subdivision even over major biogeographic features in the region, such as the French Broad River valley. By analyzing 10 of these well-sampled species with population genetic and phylogeographic methods, we found that only a few showed significant population level subdivisions. We suggest that the ballooning behavior of most immature araneomorph spiders is sufficiently frequent to overcome divergence of otherwise isolated populations, and that in those few exceptions the species are more specialized to particular microhabitats in the spruce-fir forest and such unpredictable dispersal may have been selected against.

Systemic optimization of RNA extraction protocols in non-model arachnids is indispensable for gene expression studies, including transcriptome sequencing and analyses. Spinnerets of the Neotropical tarantula Grammostola actaeon (Pocock, 1903) (family Theraphosidae) were used to evaluate the performance of two RNA extraction reagents and three commercially available kits for isolating total RNA from small eukaryotic tissue samples. Total RNA was extracted from spinneret tissues, using two samples for each method. We used the commercially available reagents TRIzol and NucleoZOL and the RNA extraction kits NucleoSpin and NucleoSpin XS (Macherey Nagel) and Total RNA Purification Kit (Norgen Biotek Corp). Quantification using Qubit revealed that NucleoSpin, Norgen, and NucleoSpin XS resulted in the highest RNA yields respectively, while Nanodrop analysis ranked Norgen, TRIzol, NucleoSpin, NucleoSpin XS in descending order. Bioanalyzer analysis indicated that Nucleospin, and NucleoSpin XS delivered the best results for our samples. While each method successfully yielded sufficient RNA for RNA-seq experiments, variations in RNA quality among methods indicate differences in their suitability for specific applications. Our data provide further evidence that RNA integrity number (RIN)-based assessments in G. actaeon may not be reliable for evaluating RNA quality due to a widespread occurrence of the ‘gap deletion’ phenomenon in arthropods. RNA from species with 28S rRNA collapsed can yield high-quality transcriptomes, suggesting that current RIN-based assessments may not be reliable for evaluating RNA quality in many non-model invertebrates. Overall, differences in results of commercially available RNA extraction reagents/kits should be considered when selecting the most appropriate RNA extraction method for gene expression analysis.

Spiders possess multiple types of silk glands, producing silk materials with contrasting properties, which are deployed in distinct behavioral contexts, such as locomotion, prey capture and egg casing. Whereas the diversity of silk glands and spigots across different spider families is relatively well described, their biological functions (i.e., with which behavior each gland type is activated) are poorly known. Here we provide an overview about available methods and approaches to determine the biological function of spider silk glands, and evaluate their advantages and disadvantages based on our experiences and a test study on Pholcus phalangioides (Fuesslin, 1775) (Pholcidae) and Kukulcania hibernalis (Hentz, 1842) (Filistatidae). 

Orb web weaving spiders, like Argiope trifasciata (Forsskål, 1775), rely on sticky aggregate glue droplets on the capture spiral of their web to retain prey. Here, we compared the protein composition of the glue droplets placed at the bottom of the web early in capture spiral construction, to those placed at the inside of the web late in web construction. We found a lower abundance of aggregate proteins in the inner web, where the droplets are smaller, are less extensible, and contain a higher proportion of water. Interestingly, we also found that pyriform spidroin, which anchors bridging lines of the web to the substrate, was more abundant in the inner region of the web, which has a higher density of capture spiral-radial line junctions. We propose that pyriform spidroin has a previously unidentified role in orb webs: anchoring the capture spiral to radial lines.

Among the variety of wolf spiders in Europe, there are some uncommon and poorly known species. An example is Pardosa paludicola (Clerck, 1757), which is classified as endangered and rare in some countries. We used a capture-mark-recapture method to examine the biology of mature P. paludicola individuals, focusing on the movement ranges of this spider. We marked 714 individuals and more than 10% of them were recaptured (♂ 4.5% and ♀ 14.7%). The median movement range was calculated at 5–6 m for both sexes and the maximum distances reached 58–69 m in 3–4 days. In the context of conservation efforts for this species, it seems important to provide large open areas of high humidity, with low human interference.

In this study, we provide an update on the knowledge of vertebrate-eating jumping spiders. Twenty-four reports of jumping spider predation on vertebrates are known, which are attributed to seven species: Hyllus diardi (Walckenaer, 1837), H. semicupreus (Simon, 1885), H. treleaveni GW Peckham & EG Peckham, 1902, Paraphidippus cf. aurantius, Phidippus bidentatus FO Pickard-Cambridge, 1901, P. regius CL Koch, 1846, and an unknown species apparently related to Hasarius Simon, 1871. In addition, several unsuccessful predation attempts by Phidippus audax (Hentz, 1845) on hummingbird and chickadee nestlings are documented. Furthermore, an incident of Phidippus otiosus (Hentz, 1846) feeding on an oversized gecko carcass (likely a case of scavenging) is reported. Overall, incidents of vertebrate predation by salticids are likely to be, in most cases, very rare chance encounters between a tiny vertebrate and a hungry spider. In contrast, the case of Phidippus regius is unique for salticids as—to the current state of knowledge—this is the only salticid species in which vertebrate consumption has been reported numerous times (n = 18) and in many different locations (11 different Florida counties, USA).

Wolf spiders (Araneae: Lycosidae) in the genus Schizocosa Chamberlin, 1904 show a diverse array of male courtship behaviors, signaling modes and morphological traits, and have been the subject of extensive study. Although S. saltatrix (Hentz, 1844) is not as well-studied as some of its congeners, this species occupies a phylogenetic position basal to the well-studied ocreata clade within the genus. Here, we present a detailed analyses of its courtship and provide some insights about multimodal signals in the genus Schizocosa. Male and female S. saltatrix were collected from the field and raised to maturity in the lab, then paired randomly for mating trials, in which courtship and mating behaviors were recorded. Male courtship displays consist of vibratory signals coupled with leg-raising visual signals, suggesting that males apparently use complex (multimodal) signals in courtship despite assumptions from other studies. While the overall amplitude of vibratory signals is not related to mating success, rates and amplitude of some individual components (leg strikes) appear to play a role. Female responses show that variation in visual and vibratory signals is associated with receptivity and mating success, although signal information content (e.g., body condition) is unclear. Although visual displays may serve as attention-altering signals and attract female attention, vibratory signals are more important to receptivity. Recent phylogenies suggest that while leg decorations, extensive leg pigmentation and visual signals have likely been secondarily lost, visual displays are retained in S. saltatrix, perhaps as attention-altering signals.

The reproductive phenology of a species of phalangiid harvestmen, Odiellus aspersus, was studied at Maruyama Park, Sapporo, Hokkaido, for the difference in adult emergence between males and females. At the timepoint in which 50% of the population had matured to adulthood, more females were represented than males, and adult females developed about 10 days earlier on average than males. There was no difference in adult body size between males that had matured earlier and males that were collected later in the season. This fact would conflict with a plausible hypothesis that males should mature slowly to attain larger body size in this species. Elongation of spermatheca in females of the species may explain the marked difference in the adult emergence in the species, by enhancing sperm priority of the males that copulated with females last.

The reproductive phenology of Himalphalangium spinulatum (Roewer, 1911) (Eupnoi: Phalangiidae), which overwinter as juveniles and mature in early summer, was surveyed at a riparian forest on the Sendai River, Tottori City, Honshu, Japan. Females became adults about 3–4 days earlier than males. The body weight of females and males and the number of mature eggs retained in females were highest at the age about a week after the final molting, suggesting a shorter time is needed to commence mating and oviposition in this species. This might be the reason for the shorter time lag in maturation between females and males in this species compared to other species of protogynous harvestmen.

Net-casting spiders (Deinopidae) are cribellate spiders that spin a rectangular, sticky net that is held stretched between the claws of their first two pairs of legs. Deinopids produce eight distinct silk types, but knowledge of the silk-producing morphologies is mostly limited to the spigots associated with different fibers. As there have been no studies of deinopid silk gland structure, we dissected all the silk glands from Deinopis spinosa Marx, 1889 and document their number and morphology. We found silk gland position and morphology consistent with the type and number of silk spigots described for Deinopidae. Notably, for the first time, we describe the silk glands associated with cribellate silk: paracribellate, pseudoflagelliform, and cribellar silk glands. Our findings support the homology of pseudoflagelliform glands with araneoid flagelliform glands and will have importance for informing our understanding of spider web evolution.

Aversive conditioning is a form of associative learning. Here, we investigated learning and memory capacity of the harvester Mischonyx squalidus (Roewer, 1913), to examine the formation of short (STM) and long-term memories (LTM). First, we trained harvesters to associate an aversive stimulus (shock) with a neutral stimulus (tea odor). Each subject went through three consecutive trials, in which pairings between the stimuli lasted for 3s, with intervals of 1 (STM) and 30 (LTM) min. Subsequently, to test memory, we introduced the subjects in a choice arena where they could choose between staying in either of two areas: impregnated with tea chemicals or blank. We did this immediately after the conditioning phase or 24h after it. Both protocols were successful for STM within the same-day test, but not for LTM on the following day. In summary, we provide a new method to train aversive conditioning in harvesters and evidence for short-term memory.