Although scorpions are common and potentially ecologically important members of arid ecosystems throughout the world, basic life history information is lacking for most species. In the current study I examined reproductive investment patterns in four species of scorpion (Centruroides exilicauda, Vaejovis spinigerus, Diplocentrus peloncillensis, and Pseudouroctonus apacheanus) from southeastern Arizona and southwestern New Mexico during 1996–1998. Vaejovis spinigerus invested more in reproduction, in both absolute (total litter mass, TLM) and relative (TLM divided by female mass) terms, than did the other species, and produced the largest litters. Offspring of D. peloncillensis were the largest, weighing over twice as much as the next largest juveniles. Female size was uncorrelated with offspring size in any species, but positive correlations were found between female size and both litter size and total litter mass for C. exilicauda (marginally significant) and V. spinigerus (after removal of an outlier). Greater reproductive investment, measured as TLM, was used to make more offspring (in all species but P. apacheanus) but not larger offspring. A marginally significant trade-off between offspring size and number was found in V. spinigerus; there was no size-number trade-off in the other three species. Overall, then, my results suggest that (1) larger females do not produce larger offspring, (2) larger females may produce more offspring and invest more into a reproductive bout, and (3) the allocation strategy of these species appears to be to invest reproductive resources into production of as many offspring as possible of a relatively fixed size.

The harvestman Ilhaia cuspidata was studied in Curitiba, state of Paraná, Brazil. The site studied is a 30,000 m² forest remnant of Araucaria forest surrounded by houses. Harvestmen were sampled 21 times over 14 months (June 1997–August 1998); at intervals of 21–30 days. The population size was estimated by Fisher-Ford and Jolly methods, and did not vary considerably from autumn (June) to spring (November 1997). However, it increased rapidly (300 %) during late spring and summer (December– March). The lowest population size estimated was 1,429 adults/subadults, during the winter (June 1997) and, the highest was 14,445 during the autumn (April 1998). The recapture rates ranged from 16%–41%. The sex ratio observed in all sampling periods was 1:1. The density varied from 0.05 (winter) to 0.47 adult subadults/m² (autumn). The extremely different abundances observed between seasons could have been influenced by temperature. The immatures were observed all year, suggesting a continuous reproduction, but they were much more abundant during spring and summer. Ecological aspects including aggregation, individual movement and life span were also discussed.

Spiders in the family Linyphiidae are numerically dominant and show remarkably high diversity in northern forests, but relatively little is known about their phenology in northern latitudes of North America. We report a phenological summary of close to 6,000 individual linyphiids representing 17 species. These were collected by pitfall trapping during two snow-free seasons in an old-growth deciduous boreal forest in central Alberta, Canada. Three species of approximately the same body size, Allomengea dentisetis (Grübe 1861), Bathyphantes pallidus (Banks 1892), and Lepthyphantes intricatus (Emerton 1911), dominated the sample, and showed three distinct patterns of peak activity. This suggests temporal stratification as a possible mechanism that explains their co-existence. Four less commonly collected species within the same genus (Walckenaeria) showed similar seasonal segregation in periods of peak activity. Comparisons with other literature suggest the general phenology of many linyphiids is conserved across continental and global scales.

The spider genus Calileptoneta Platnick is revised and all species are described, diagnosed and keyed. A neotype for Calileptoneta californica (Banks) is designated and Calileptoneta sylva (Chamberlin & Ivie) is removed from synonymy with Calileptoneta californica (Banks). The female of Calileptoneta noyoana Gertsch and the male of Calileptoneta sylva (Chamberlin & Ivie) are described for the first time. Three new species are described: Calileptoneta briggsi, Calileptoneta cokendolpheri, and Calileptoneta ubicki. The morphology of Calileptoneta is discussed, and interpretive illustrations of male and female genitalia are provided. The natural history of Calileptoneta is presented with an account of the mating behavior for C. ubicki. The distribution of Calileptoneta species is discussed, and areas of endemism and potentially new Calileptoneta species are noted.

Three new species of the genus Phrurolithus are described from the Gaoligong Mountain Region of Yunnan Province, China: Phrurolithus bifidus, P. qiqiensis and P. revolutus.

Adult male animals are commonly believed to exhibit higher activity than other conspecifics, but little information exists to compare their activity with that of other conspecifics of similar size. Here we compare the activity of adult male and similar-sized juvenile female crab spiders Misumena vatia (Araneae, Thomisidae). Adult males moved farther and more frequently than juvenile females of similar size (fourth instar) that were not affected by impending molt. Juvenile females influenced by impending or recent molt did not move as far or as frequently as nonmolting juveniles, even though their exoskeletons were hard enough to permit rapid movement. A small sample of penultimate males, of similar size to the adult males and juvenile females, exhibited activity patterns similar to the juvenile females. All of these data indicate that the high activity level of adult males is not a simple manifestation of behavior that is solely a function of size. We suggest that the high activity levels of the adult males facilitate search for scarce, cryptic mates.

The scaber group of the genus Eremobates is reviewed in terms of new characters and a more restricted biogeographic area. Three new species are described from the U.S.A.: Eremobates socal (California), E. icenoglei (California), E. corpink (Utah). We synonymize E. gladiolus Muma with E. scaber (Kraepelin); E. consors Muma, E. ascopulatus Muma and E. flavus with E. ascopulatus Muma; and E. mimbrenus Muma with E. mormonus (Roewer). Eremobates scaber, E. hodai Muma, E. clarus Muma, E. similis Muma are now described from both sexes. All scaber species except the Mexican species, E. legalis Harvey, are now known from both sexes. We also present the first phylogeny of the species group based on morphological characters. This phylogeny demonstrates a geographic grouping into northern and southern clades.

Many environmental factors influence the composition of animal assemblages. For spider assemblages, plant architecture is an important variable. Here we examine the effects of various plant architectural attributes by using models of shrubs in which we control branch orientation (horizontal or vertical) and height above the ground (0, 10, or 40 cm). Guild membership, based on hunting strategy (jumpers, pursuers, ambushers, or trappers), was used to characterize spider assemblages. Five replicates of the six treatments (two orientations by three heights) were randomly placed in a 60 m by 50 m grid among big sagebrush in a shrub-steppe habitat and sampled at 3 week intervals from July–October in 1997 and 1998. ANOVA was used to demonstrate that not only do single architectural variables influence the distribution of spiders but also the interaction of architectural variables influence spider distribution. Differences in the assemblages of spiders on the models were the result of architecture differences. Jumpers selected horizontal, 10 cm models and pursuers selected vertical, 0 cm models. Trappers were most abundant on horizontal, 0 cm models.

Spiderlings of the theraphosid spider Hysterocrates gigas were reared for 12 weeks with a superabundance of prey solitarily and in groups of two and four to examine the influence of rearing group size on growth. This taxon was selected because observations made on captive populations indicate that Hysterocrates spp. tarantulas have an unusually high level of mutual tolerance and captive juveniles have been observed to feed cooperatively on large prey until several months old. Cannibalism was only observed in one instance, in a group of four. There was no significant effect of rearing group size on increase in body mass. There was a tendency for a greater asymmetry in final weight in dyads than in tetrads. No difference was found in the amount of time spent feeding by individuals between the different group sizes. Hence, benefits of group living in Hysterocrates gigas spiderlings were not evident in this study.

A new species, Micrathena cicuta, is described and illustrated based on females from southeastern Brazil. Plectana degeeri Walckenaer is synonymized with M. plana (C.L. Koch), based upon the original description.

We document the first case of a color dimorphism in a pholcid spider. Males, females and juveniles of Buitinga safura Huber 2003 either have large black spots on the abdomen or no spots, with no intermediates. At the same time, this species shows sexual dimorphism (brown prosomal marks present in males only) and continuous prosomal pattern variation in males, females and juveniles. The abdominal pigment is located in the hypodermis.

Adult females of the wolf spider Pardosa milvina (Hentz 1844) are known to show adaptive antipredator responses in the presence of chemical cues (silk and excreta) from the larger co-occurring wolf spider Hogna helluo (Walckenaer 1837). We tested if the presence of H. helluo cues affected P. milvina spiderling dismounts from their mothers. Immediately after females opened their egg sacs, we counted offspring and placed spiderling-carrying females on one of three experimental substrates: 1) container previously occupied for 24 h by an adult conspecific female, 2) container previously occupied for 24 h by a juvenile H. helluo equal in mass to an adult P. milvina, or 3) a control container devoid of either cue. We then measured the proportion of spiderlings that dismounted from their mothers over a six-day period. Spiderling dismounts peaked by day three, after which spiderlings tended to return to their mother. During day one, significantly fewer spiderlings were dismounted from the mother in containers previously occupied by a juvenile H. helluo compared to other treatments. There was no significant difference in dismounts among treatments during days 2–6. Since spiderlings were maximally dismounted by day three, we suggest that spiderlings may tend to disperse into areas with fewer H. helluo.

Reproductive stems add complexity to vegetation, thereby increasing the range and quality of microhabitats available for arthropods. In this study, we evaluated whether variation in inflorescence characteristics influenced spider distribution. We compared spider guild structure among inflorescences of three herbaceous plant species, Melanthera latifolia, Conyza bonariensis and Eupatorium hecatanthum (Asteraceae), and between inflorescences of C. bonariensis in two different phenological stages, flower buds and opened flowers. Total spider abundance was higher on M. latifolia, intermediate on E. hecatanthum, and lower on C. bonariensis. Ambush spiders were more abundant on M. latifolia than on the other plant species, while the abundance of hunting spiders did not differ among plant species. Also, spiders recorded on M. latifolia were larger than those on both E. hecatanthum and C. bonariensis. However, ambush spiders were smallest on M. latifolia, while hunting spiders on E. hecatanthum were larger than on the other plant species. The number of spiders on inflorescences with flower buds did not differ from those with opened flowers, but ambush spiders on inflorescences with opened flowers were larger than those on inflorescences with flower buds. Our results with different inflorescence types support the hypothesis that differences on microhabitat structure influence distribution of spiders.

The taxonomic status of two closely related species of Latrodectus, L. mactans and L. hesperus, has been debated for many years. Based on morphological characteristics and genitalia, some workers consider them as valid species and others as subspecies. This study was conducted to determine whether the internal transcribed spacers 2 (ITS2) of rDNA exhibit sequence differences between the two taxa that could delineate their taxonomic relationship. Individuals of L. mactans and L. hesperus from six populations were collected and identified based on morphological characteristics. The ITS2 rDNA of nine individuals was sequenced and analyzed. Results indicate that the minimal differences present in the ITS2 sequences are taxonomically insignificant.