Vinegaroons are members of a guild of apex arthropod predators in the high desert grasslands of southeastern Arizona. Despite their importance as major predators in the ecosystem, almost nothing is known about their potential prey, predators, or competitors. We evaluated predator-prey relationships of vinegaroons and 30 species of potential prey, 27 species of potential predators, and the detailed interactions among three taxa of their apex predator guild. With few exceptions, vinegaroons overpowered and preyed on most potential prey within a suitable size range, were almost immune to predation, and appeared to be the dominant species in interactions with other predator guild members. Their most vulnerable life stages were the first two free-living instar stages, whereas adults and fourth instar individuals were not preyed on by any predators active in the same areas and times as vinegaroons. Third instar individuals were a crucial transition stage in which they had a few predators but also were large enough that they required capturing many prey items to grow sufficiently to molt to the fourth instar. In interactions among arthropod predators, the general observation was that when predation occurred, the larger individual usually prevailed irrespective of taxon. Cannibalism among adult and fourth instar vinegaroons does not occur under natural conditions in contrast to when they are placed together in artificial stressful situations. Cannibalism of the three smallest instars appears likely and might partially explain why they are solitary and spend minimal time foraging.

Group-living spiders are rare, and can be divided into multiple subcategories based on their tolerance of group mates. While social spiders are cooperative, colonial spiders are often antagonistic towards conspecifics. We examined colony dynamics in a colonial species, Philoponella republicana (Simon, 1891), focusing on aggressive behaviors to further understand this understudied species. We studied whether web region, sex ratio, web size, or spider size affected aggression. We also tested whether colony members discriminate against conspecific intruders, since this behavior, known as group closure, is prevalent in many other group-living animals but had not yet been tested in colonial spiders. Colony mates were often aggressive due to competition for limited resources, such as mates and orb webs, yet several characteristics of this species may reduce these competitive forces. First, female-biased secondary sex ratios appear to reduce male-male and female-male competition. Moreover, although some individuals defended orb webs, other areas in the communal web were not defended. Philoponella republicana also did not exhibit group closure. Our results further confirm that aggression between males decreases in colonies with more female-biased secondary sex ratios, and larger individuals correlate with a higher frequency of aggressive interactions. Moreover, we raise new questions concerning the evolutionary pressures that shape coloniality in spiders.

Supplemental Materials

Table S1.—Effects of inter-colony translocation treatment on responses of Philoponella republicana.  - Download file

Table S2.—Results of inter-colony translocation experiment. - Download file

We describe two new Nesticus Thorell, 1869 from Walker County, Georgia, USA. Nesticus lula sp. nov. is known from two caves on the eastern edge of Lookout Mountain and N. cressleri sp. nov. is known from three caves on Pigeon Mountain. Morphological and molecular evidence indicates the distinctiveness of both species when compared to other Nesticus from the southern Appalachians. Nesticus lula has reduced eyes and N. cressleri is eyeless. Both species are of conservation concern, as they are known from only a handful of sites spanning extremely limited ranges. This work contributes to our understanding of cave biodiversity in Georgia and of the Nesticus radiation in the southern Appalachians.

Ballus Koch, 1850 is a beetle-like jumping spider genus encountered in montane evergreen rainforests of the Central and Uva Provinces of Sri Lanka. The taxonomic literature documents three species of the genus for the island. However, neither the taxonomic validity nor the systematics of any of the three species have been previously examined. We used nuclear and mitochondrial DNA sequences (28S rRNA, H3, COI) as well as morphological characters to investigate the genetic and taxonomic diversity of Ballus populations in Sri Lanka, including specimens from type localities. No Ballus specimens were found outside of the central highlands. Results of molecular species delimitation and morphological analysis suggest the presence of only a single species of Ballus in Sri Lanka. We therefore propose B. sellatus Simon, 1900 to be a junior synonym of B. segmentatus Simon, 1900, while B. clathratus Simon, 1901 remains a nomen nudum. Further, we discuss the implications of our results for conservation planning.

Animals may build nests socially to minimize the energy required for nest construction. Paratemnoides spp. pseudoscorpions evolved sociality independently from all other social groups, and colonies create silken multi-chambered nests in which they molt and raise young, analogous in form to the nests of some wasps and bees. Here we describe these nests and examine pseudoscorpion construction efficiency. Silk is generally energetically expensive and as such, we hypothesized that P. elongatus build nests of a structure that minimizes silk use, thereby maximizing nest construction efficiency. We measured the number of nest chambers, their perimeter, and their area, for 31 nests, calculated several metrics of nest architecture, and developed five alternative mathematical models describing other possible nest geometries. We found that real social pseudoscorpion nests are constructed with high efficiency, measured as wall length per internal area, approaching that of mathematical optima. We also found that these nests use less silk per capita than if the same chambers were built separately, i.e., if they were solitary. This indicates a direct benefit to group members. We compared observed nest architecture with five mathematical models of nest geometry and found that pseudoscorpion construction efficiency outperformed all non-cooperative models and rivaled that of a cooperative one approximating the honeycomb conjecture - a mathematical proof describing the most efficient way possible to divide a 2-dimensional plane. In summary, social pseudoscorpions design group nests with multiple chambers in a way that minimizes wall length per internal area and approaches the efficiency of honey-bee-like hexagon constructcion.

“Primary” webs of uloborids have large numbers of very fine lines and usually lack sticky cribellum silk. This paper reviews their taxonomic distribution (19 species in 5 genera) and the ontogenetic stages in which primary webs are built (spiderlings newly emerged from the egg sac, older juveniles, mature males, and normal and senile females), expands the knowledge of construction behavior, and describes several previously unnoticed design details. Primary webs differ from typical uloborid orbs in several ways: large numbers of fine radial and non-radial lines; facultative hub removal and replacement; usually closely spaced temporary spiral loops; and lines beyond the frame lines. Construction of supplemental radii in primary webs is distinctive in several respects: break and reel construction; tendencies to lay successive radii either on opposite sides of the web or close together in the same sector; high frequencies of aborted trips from the hub to the frame; production of multiple lines during a single trip from the hub to the frame and back; long pauses during the production of single radii; and variation in the sequences in which radial lines are added to a given sector. Some aspects of primary web construction resemble araneoid rather than typical uloborid behavior. The relation between primary webs and the evolution of orb webs, and the mechanism that spiders use to produce abundant non-radial lines despite making only radial movements during web construction remain uncertain. We speculate that primary webs are favored when spiders are unable to afford the costs of producing cribellate silk for a typical orb.

Web designs have long been used to characterize spider taxa and to deduce the relations between them; but systematic documentation of the amount of variation in webs within and between taxonomic groups is rare. This study, based on previously published observations and new observations of 15 species in the family Uloboridae, including two genera, Octonoba Opell, 1979 and Siratoba Opell, 1979, whose webs were previously undocumented, reviews the taxonomic distribution and variation in 22 orb web traits in at least 43 species in 11 genera in uloborids. These traits appear to occur in all orb-weaving genera in which reasonable samples are available, though only small samples are available for many species. Larger samples of the webs of three species of Uloborus Latreille, 1806, two of Hyptiotes Walckenaer, 1837, and one each of Zosis Walckenaer, 1841, Siratoba, Octonoba, Waitkera Opell, 1979 and Philoponella Mello-Leitão, 1917, revealed greater intra-specific consistencies in some traits than others. Hub traits were especially consistent. Variations in three traits may represent adjustments to the size of the space in which the orb is built. “Primary” webs, which combine orb and sheet-web traits, are built by spiderlings newly emerged from the egg sac and by adult males in at least five genera of orb-weaving uloborids and may be unique to this family. Preliminary comparisons between uloborid and araneoid orbs suggest that uloborid orbs may also differ from araneoid orbs in combining several other traits.

Metabolism powers all of life's processes, making it fundamental to understanding organisms in nature. For many arachnids, however, we do not have direct measurements of either metabolic rate or the relationship between metabolic rate and body size (i.e., allometric scaling, an important determinant of metabolic rate). Here, we present the first measurements of metabolic rate and allometric scaling in a stridulating spined micrathena spider, Micrathena gracilis (Walckenaer, 1805). Since intraspecific variation in metabolic rate may provide insights into variation in energetically costly behaviors, we additionally explore the link between stridulation and metabolism in M. gracilis. Our data suggests a link between stridulatory behavior and allometric scaling, such that increased stridulation is associated with a weaker connection between body mass and metabolic rate. We discuss how links between energetics, expression of behavior, and body size inform our understanding of trait variation in these spiders.

Supplemental Materials

Figure S1.—Correlation between opisthosoma length and mass. Table S1.—Models for respiration ranked by AIC. - Download file

We analysed the dead-wood characteristics that determine the presence of saproxylic pseudoscorpion species in remnants of riparian cloud forest. We examined 98 dead-wood pieces (70 logs and 28 stumps), and recorded tree species, decaying wood stages, presence of the pseudoscorpion Lustrochernes grossus (Banks, 1893) (Chernetidae) and the Bess beetle Helicus tropicus. In these wood samples we found 24 L. grossus and one chela. We recorded the highest number of individuals in Clethra mexicana (11), followed by Quercus corrugata (6) and Liquidambar styraciflua (6). In Annona cherimola and Trema micrantha, one chela and one female were recorded, respectively. The presence of this pseudoscorpion is likely due to its relationship with the Bess beetle, which coexists in decaying wood. The distribution of L. grossus in dead wood may also be influenced by tree species and stage of decay. Forest fragmentation and the extraction of firewood from the remnant riparian fragments of cloud forest are factors that could jeopardize the saproxylic pseudoscorpion species and other arthropod diversity associated with decaying wood in this threatened ecosystem.