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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.

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.

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. 

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. 

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.

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.

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.

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