Certain joints in the pedipalps of scorpions and sun-spiders lack extensor muscles but have elastic transarticular sclerites that store energy during flexion and return energy as elastic recoil during extension. This study quantifies the extension torque contributed by elastic recoil and hydraulic pressure in the chela (tibia–tarsus) and femur–patella joints of scorpions and the patella–tibia and tibi-tarsus joints of sun-spiders. Extension torque was measured as isolated joints were cycled through a natural range of angles and angular velocities by a computer controlled stepper motor. Resilience (efficiency of elastic energy return) of transarticular sclerites in the absence of internal fluid pressure was about 60% in scorpion joints and 80% in sun-spider joints. Elastic torque increased almost linearly with flexion angle in most joints except in the scorpion chela, where elastic torque decreased rapidly as the fully closed joint began to open, increased gradually and then decreased again near the fully open position. Hydraulic pressure contributed more to extension of pedipalpal joints of scorpions than those of sun-spiders. Our results indicate that mechanical properties of a “passive” transarticular sclerite can be changed by altering internal fluid pressure and by capitalizing on the sclerite's intrinsic viscoelasticity.

A variety of arthropods forage and avoid predators via locomotion on the surfaces of ponds and streams. For these animals, cuticular hydrophobicity functions to keep them dry and well supported by the water's surface tension, and also allows them to move easily between wet and dry habitats. Among spiders, members of the family Pisauridae exemplify this semi-aquatic lifestyle and, not surprisingly, these spiders remain entirely dry even when submerged. In the current study, we sought to quantify the degree to which spiders in a variety of families resist wetting by liquid water. Two properties of a spider's cuticular hairs are predominant in determining this resistance: adhesion energy (a consequence of molecular interactions between the hair surface and water) and hair density. When hair density is low, the adhesion energy of the cuticle itself also plays a role. Among the ten families we studied, pisaurids and pholcids defined the ends of the spectrum of resistance, with the pisaurids nearly 50 times more resistant to wetting than the pholcids. We discuss both the impact of this variation on spiders' potential for aquatic locomotion and the variety of selective forces that may have contributed to this impressive variation in capabilities.

In this study, we provide an ethogram for the harvestman Ilhaia cuspidata and describe the daily activity pattern of captive individuals. We also provide a comparison between the behavioral repertory of this species with that of the syntopic Discocyrtus oliverioi. Five females and four males of I. cuspidata were maintained in the same terrarium from November 1999–November 2000 for qualitative and quantitative observations. Twenty behavioral acts were recorded, classified in seven categories and the relative frequency of each was determined: exploration (69.8%), resting (16.7%), feeding (6.3%), grooming (4.4%), social interactions (2.6%), reproduction (0.1%) and others (0.3%). There was a marked difference in the frequency of the behavioral categories between sexes: females fed more frequently than males and males were involved in social interactions more frequently than females. During most of the daylight hours, individuals remained inside shelters and became active from 19:00–09:00 h. Although I. cuspidata and D. oliverioi showed almost the same behavioral acts, there were quantitative differences in their repertories: the relative frequency of behavioral categories “resting” and “social interactions” were higher for I. cuspidata whereas “reproduction” and “grooming” were higher for D. oliverioi. The main qualitative difference between these two species was related to the forms of parental care: females of D. oliverioi guard their eggs and first instar juveniles, whereas females of I. cuspidata scatter their eggs in time and space and do not actively protect their offspring. Since both species share the same habitats (sometimes in multi-species aggregations), the behavioral differences between them may be explained by particular morphological and physiological characteristics of the species, as well as by phylogenetic constraints.

Prey specialization and the predatory behavior of two European ant-eating zodariid spiders, Zodarion germanicum and Zodarion rubidum, were studied in detail. The spiders were offered 12 ant species and seven other insects (termites, beetles, aphids, silverfish, flies, crickets and grasshoppers). Study spiders turned out to be ant specialists as they were able to subdue many ant species but ignored all other insects, except termites, which they attacked but rarely subdued. The best capture success was obtained with medium-sized ants (e.g. Lasius and Formica). The predatory behavior of the zodariid spiders involves an attacking and a handling phase separated by a period of waiting at a safe distance. The attacking phase consisted of a very rapid lunge from the rear, followed by a bite on the most extended ant leg. After an attack, the spider retreated to a safe distance, perhaps an indication that natural selection has favored such caution in the presence of an aggressive prey. The spider waited until the ant ceased moving. Such predatory behavior, which limits contact with the predator and prey, is clearly an effective means of handling a dangerous prey.

We report on the natural history and web building behavior of the South American austrochilids Thaida peculiaris and Austrochilus forsteri, relatively basal lineages within Araneomorphae. Species of these two cribellate genera construct large, two-dimensional sheet webs with a funnel retreat. When combing cribellate silk, austrochilids use both fourth legs, like entelegyne spiders, and unlike Hypochilidae and Filistatidae. Furthermore, the alternancy of combing legs IV is determined by the leg III involved in the attachment of a cribellate segment; the leg IV ipsilateral to the leg III that made the attachment will comb the next segment, except for the first segment. This similarity to Entelegynae in combing with both fourth legs contradicts current hypotheses of basal araneomorph relationships and suggests that the Austrochilidae may be the sister group of entelegyne spiders.

In the 48 contiguous United States, the wolf spider subfamily Pardosinae is represented by 65 species of Pardosa and 1 species of Acantholycosa. This study provides a comprehensive account of all species of Pardosinae in the USA including keys, some of which are new, for their identification. Based on genital morphology, the species of Pardosa in the USA can be divided into 14 species groups containing from one to 17 species. The male of P. ourayensis Gertsch 1933 is illustrated for the first time. Difficulties arise in the identification of some sister species which are both morphologically and geographically close; and also many of the species in the sternalis group which can be identified only by their distribution.

The southern African species of Parabuthus Pocock 1890 are reviewed. Twenty valid species are recognized and an illustrated key is provided for their identification. The diagnosis of each species is revised, its known distributional range summarized, and notes on its ecology and conservation provided. Three species are redescribed and their distributions mapped: P. calvus Purcell 1898; P. capensis (Ehrenberg 1831); P. planicauda (Pocock 1896). Six new synonyms are proposed: Buthus brevimanus var. β segnis Thorell 1876 = P. granulatus (Ehrenberg 1831); Buthus villosus var. β dilutus Thorell 1876 = P. raudus (Simon 1888); P. granulatus strenuus Hewitt 1918 = P. granulatus (Ehrenberg 1831); P. capensis frenchi Purcell 1901 = P. planicauda (Pocock 1889); Scorpio teter Müller 1828 = P. transvaalicus Purcell 1899; P. brachystylus Lawrence 1928 = P. villosus (Peters 1862). Two species, synonymized by previous authors, but subsequently resurrected, are returned to synonymy: P. neglectus Purcell 1899 = P. capensis (Ehrenberg 1831), first synonymized by Kraepelin (1908); P. flavidus Pocock 1899 = P. mossambicensis (Peters 1861), first synonymized by Kraepelin (1914).

Eustiromastix nativo new species is described and illustrated based on specimens collected from bromeliads in northeastern and southeastern Brazil.