Many spiders eat mosquitoes, but a spider is not automatically a mosquito specialist if it eats mosquitoes, or even if it primarily eats mosquitoes. Instead, specialization pertains to predators being adaptively fine tuned to specific types of prey. It is important to keep this basic meaning of specialization conceptually distinct from diet breadth (stenophagy versus euryphagy), adaptive trade-offs and other sister topics. Here we review the biology of Evarcha culicivora Wesolowska & Jackson 2003 and Paracyrba wanlessi Żabka & Kovac 1996 (Salticidae), two spider species that can be characterized, in their own individual ways, as being mosquito specialists. However, simply calling these species mosquito specialists can be misleading. Details matter, with some of the most important of these details pertaining to the different ways E. culicivora and P. wanlessi classify mosquitoes. The way these species classify, and specialize on, mosquitoes includes fine-tuned prey-choice behavior, special feature-detection mechanisms, deployment of selective attention and other behavioral and cognitive capacities that can be understood only on the basis of appropriately designed experiments.

Predators often adopt strategies to capture prey that reflect both the characteristics of the prey and their own hunger level. In generalist spiders of the family Salticidae, predatory behavior typically consists of four phases: orientation towards the prey, pursuit, crouching, and jumping to capture. In this study, we conducted laboratory experiments in order to determine whether predatory strategies change according to prey type and hunger level in Corythalia albicincta (F. O. Pickard-Cambridge 1901). We used adult specimens of both sexes to evaluate variation in capture jump distance, time spent on each predatory stage and attack efficiency, in terms of prey capture. Jump distance was greater with prey that can more readily escape (crickets and flies), compared to fly larvae. The duration of both latency and orientation was greater in larval trials than in the cricket and fly trials. Corythalia albicincta spent less time in a crouching position with flies and the total duration of the predation process was shorter with flies than with crickets or larvae. Numbers of failures, defined as the number of failed attacks before a spider captures a prey item in the test, was higher in spiders that had been starved for one day compared to those that had been starved for 7 and 15 days. Predatory strategies were modified according to movement patterns and prey speed, while hunger level affected predation efficiency.

Each of the droplets that form an orb-weaving spider's viscous capture thread are composed of a viscoelastic glycoprotein glue core that is surrounded by an aqueous layer and supported by a pair of protein axial fibers. Low molecular weight organic and inorganic compounds within the aqueous layer confer droplet hygroscopicity, thereby maintaining the glycoprotein's adhesion and extensibility and ensuring that the axial fibers remain supercontracted. These materials also cause droplet volume to change in response to ambient humidity. This study examined the viscous threads of Argiope aurantia Lucas 1833, a species found in exposed, low humidity habitats, and Neoscona crucifera (Lucas 1838), a nocturnal species found in high humidity forest edge habitats. An earlier study showed the former species' threads to be more hygroscopic than those of the latter. When aged and exposed to chemical fixatives, the hygroscopicity of A. aurantia threads decreased, while that of N. crucifera threads was unaffected. Fixation eliminated the extensibility of both species' droplets. However, droplet adhesion, as measured by the deflection angle of a thread's axial lines just prior to droplet extension or, in the case of fixed droplets, droplet pull-off, was unaffected. These findings indicate that the compounds that confer greater hygroscopicity to A. aurantia viscous threads are more susceptible to chemical fixatives than those in the aqueous layer of N. crucifera droplets.

Constructing webs for survival is rare in wolf spiders. However, some species, postulated as basal in the family, live in funnel-webs. Aglaoctenus lagotis (Holmberg 1876), a South American lycosid, lives permanently in webs. It is virtually unknown how web construction occurs for this species and the few other lycosid weavers. Also, costs associated with construction have not been studied, although funnels are suggested to be particularly costly webs. This study describes the funnel-web construction behavior of A. lagotis (Lycosidae: Sosippinae) and measures its costs in subadult and adult individuals. We recorded web construction, effects of sealing spinnerets in weaving activity, and immune costs of weaving (measuring melanization of an implant) in individuals allowed to weave and prevented from weaving. Construction consisted of three alternating behaviors: deposition of thick threads with a radial orientation and prolonged attachments (mainly involving the anterior spinnerets); deposition of swaths of fine threads without consistent orientation and with short attachments (mainly involving the posterior spinnerets); and motionlessness. No sticky threads are present in the web. The thick threads have a supporting function and the fine threads have a filling function. Subadults and males allowed to weave reduced their immune response compared with those prevented from weaving; no such relationship was observed for females. Males presented the weakest immune response, followed by subadults and females. The web construction process showed greater similarity with agelenid spiders than with the only other lycosid studied, Sosippus janus Brady 1972, and appears to be a costly activity, especially for males.

Female wolf spider silk is known to elicit searching and courtship behavior among adult males, however variation in the types of silk females deposit, the context in which it occurs, and the role of male silk in courtship displays and female responses has rarely been examined. We measured male Pardosa milvina (Hentz 1844) silk deposition while performing courtship displays. We then examined whether female silk deposition changes when encountering silk produced from a courting rather than a non-courting male and compared these conditions to female silk deposition in the absence of male silk. We measured the quantity of three different types of silk (draglines, cord silk, and attachment disks) deposited by females across substrates previously occupied by a courting male, a non-courting male, or no male. Females significantly increased attachment disk deposition in the presence of silk from a courting rather than a non-courting male. Females also showed elevated dragline deposition in the presence of male silk but whether or not the male was courting had no effect on dragline deposition. Female cord silk deposition did not vary across treatments. Courting males produced significantly fewer attachment disks than non-courting males while dragline and cord silk deposition did not vary. We conclude that females can discriminate between silk from courting and non-courting males and increase attachment disk deposition in the presence of courting males. The number of male attachment disks deposited may be one mechanism by which females can discriminate between silk produced by courting rather than non-courting males.

Within the araneomorph lineage Entelegynae, the “Higher lycosoids” (“True Lycosoids” or Lycosoidea s.s.) is one of the major clades varying in its composition based on several conflicting phylogenetic hypotheses. So far, only a few species have been studied cytogenetically. In this work, the chromosomes of a senoculid spider were investigated for the first time, along with a cytogenetic analysis of six species of the families Lycosidae and Trechaleidae. Mitotic metaphase cells of the lycosid species revealed 2n♂ = 18 X0 in Hogna sternalis (Bertkau 1880) and Lycosa nordenskjoldi Tullgren 1905, and 2n♂ = 20 X₁X₂0 in Lycosa erythrognatha Lucas 1836 and Lycosa sericovittata Mello-Leitão 1939. Chromosomal analysis of the trechaleid and senoculid species showed 2n♀ = 22 in Neoctenus comosus Simon 1897 (Trechaleidae), and 2n♂ = 26 X₁X₂0 in Syntrechalea syntrechaloides (Mello-Leitão 1941) (Trechaleidae) and Senoculus sp. (Senoculidae). This latter karyotype is a shared feature in most species of Lycosoidea group. The mitotic and/or meiotic cells of certain individuals of Trechaleidae exhibited one extra chromosome, which could constitute a B chromosome or represent intraspecific variability in the type of sex chromosome system. The results obtained here add new information to the discussion of the main mechanisms of chromosome evolution within this group.

In the present study, we examined the female genital system of a velvet spider (Eresus kollari Rossi 1846) using light and electron microscopy. The female entelegyne genitalia of E. kollari comprises an epigyne with an anterior wide longitudinal bar and folds which are incurvated sidewards. The anterior end of these folds corresponds to enlarged anterior bulges which are connected to a distinct copulatory duct leading to lobular spermathecae. The anterior bulge is equipped with many large pores whereas the spermathecae has many small pores. At present, only a few studies have focussed on the ultrastructure and possible function of adjacent epithelia in entelegyne genitalia of spiders revealing the presence of complex class 3 gland cell units around the spermathecae and ducts. Alternatively our analysis finds two different types of epithelia. The anterior bulge is equipped with class 3 gland cells whereas the spermathecae are surrounded by a putative transport epithelium. This epithelium is characterized by an extensive basal labyrinth, numerous mitochondria, and an invaginated cell apex with microvilli. The functions of the different parts are unclear, but the secretion produced by the class 3 cell glands in the anterior bulge could be involved in the transport of sperm by flushing a considerable quantity of secretion towards the posterior. Alternatively, it could also contribute to the amorphous mass which is formed during mating covering most of the epigyne. On the other hand, the epithelium around the spermathecae might only be involved in the alteration of the milieu in the spermathecal lumen but not contribute to the nutrition of spermatozoa during sperm storage.

Field and laboratory observations of the feeding ecology (natural diet, prey capture success, and prey handling) of Oecobius maculatus Simon 1870 were combined in this study to reveal the level of trophic specialization by this species. Natural prey were investigated on the Croatian island of Brac. Field observations revealed that although spiders captured prey belonging to five invertebrate orders, the most frequently captured prey were ants, which were also the most abundant available prey in the locality. In laboratory experiments, O. maculatus spiders accepted three other prey types with a higher probability than ants and were significantly more efficient at capturing and handling flies than ants. These results suggest that this species is a stenophagous generalist with a narrow prey range due to ecological circumstances.

The legs of laniatorean harvestmen feature a considerable diversity of setae, glandular openings, sensory structures, and tubercles. In this study, we compared the morphology of cuticular structures occurring on leg IV of 12 species of cosmetid harvestmen and six species of other gonyleptoidean harvestmen representing the families Agoristenidae, Gonyleptidae (three subfamilies), and Stygnidae. Our results indicate that there is considerable interspecific variation in rough pit glands and the tarsal perforated organ among cosmetid and gonyleptoidean harvestmen. We also found interspecific variation in the relative size, number, distribution, and morphology of the tubercles on the femur, patella and tibia. We observed relatively little interspecific variation in the morphology of sensilla chaetica, trichomes, spines, single pores, tarsal aggregated pores, and slit sensilla. Additional studies of the ultrastructure of cuticular structures, especially rough pit glands, are needed to assess their functional significance. Future systematic revisions of cosmetid taxa may also benefit from the inclusion of characters based upon interspecific variation in the microanatomical structures of the legs.

Preliminary observations suggested that the Neotropical harvestman Jussara sp. (Sclerosomatidae, Eupnoi) had a patchy distribution and a marked seasonality, comparable to species in the Northern hemisphere. This would be an unusual pattern, since conditions of temperature and humidity are very different between tropical and temperate environments. Using a mark-recapture method, we investigated the phenology, habitat use and individual movement of Jussara sp. in a tropical rainforest in southern Brazil. We found a very marked seasonality in the population of adults, with a positive correlation between temperature, humidity and number of adults found. Adults were found only in the wet and warm months and significantly preferred the plant Psycothria suterella (Rubiaceae) as a resting substrate, spending the days motionless on its leaves, often in groups. The same individuals were found for a maximum of three months after their first capture, 30 m from their original site of capture. At night, the harvestmen would descend from the plants, forage and interact with conspecifics on the leaf litter. In this first long term behavioral study with a representative of the suborder Eupnoi in Brazil, we provide quantitative evidence that, despite the milder climate, Neotropical harvestmen may show a seasonality similar to the seasonality shown by related species in temperate regions.

Caves are peculiar ecosystems; they are most often small, isolated habitats that lack the energy that sunlight provides. Cave-adapted species, isolated from epigean (i.e., surface) selection pressures, have been discovered with aphotic adaptations like blindness, depigmentation, and enhanced extra-optic sensory systems. This evolutionary process, however, only occurs in a fraction of cave ecosystems. Many cave species, especially those in tropical latitudes, occur with epigean conspecifics with ongoing gene flow and epigean migration. This includes populations of the amblypygid Phrynus longipes (Pocock 1894), which occur in both epigean and cave environments. I hypothesized that cave and epigean populations exhibit behavioral variation to meet the selection pressures of their respective environments. I conducted open-arena and interaction behavioral assays to test for behavioral variation between populations. Assays revealed that cave and epigean amblypygids exhibited environment-specific behavioral variation. Cave animals were more vigilant and engaged in hunting behaviors, but were less active in general, relative to epigean conspecifics. Comparative modeling indicated that aggressive behaviors during agonistic interactions were the best predictors of environment. Indeed, epigean interactions escalated to physical aggression sooner and included longer weaponry displays than did the interactions of cave conspecifics. Trial design allowed for measurements of territorial behavior, which showed that residency effects were more profound in epigean interactions than in those of cave conspecifics. The high density of amblypygids in the cave population may have resulted in more tolerant, less aggressive behaviors relative to epigean conspecifics. Thus, these findings fit the ecological and demographic conditions of each environment.

The fossil whip spider Electrophrynus mirus Petrunkevitch 1971 (Arachnida: Amblypygi: Electrophrynidae) from the Mexican Chiapas amber (Miocene: ca 15–20 Ma) is redescribed. Its original referral to an extinct family and genus based on an unusual configuration of the pedipalp is shown to be based on a misinterpretation. The family Electrophrynidae has already been synonymized with Phrynidae. Although E. mirus closely resembles modern phrynids, a key diagnostic character relating to the dorsal pattern of spines on the pedipalp patella is not preserved. Since this incomplete fossil cannot be meaningfully compared either to modern genera or to other whip spiders in Neotropical amber, we believe the pragmatic solution is to treat E. mirus as a nomen dubium.

Morphological and SEM analyses were carried out on the chorion of freshly laid eggs, eggs at different time intervals after oviposition and after hatching of a Namibian segestriid spider Ariadna sp. The eggs laid in the laboratory are held together by a milky-white mucous secretion that gradually decreases until it almost entirely disappears. The eggs are spherical/ellipsoid in shape and, only after the reduction of the secretion, are granular structures of the exochorion evident. Granules are arranged in a single layer and lie on a compact endochorion covering the thin vitelline membrane. No significant difference was found in the chorion of hatched eggs compared to eggs a few hours after oviposition.