of the spider genus Neoanagraphis (Araneae, Liocranidae)
by Richard S. Vetter
ABSTRACT.The spider genus Neoanagraphis consists of two partially sympatric species, N. chamberlini Gertsch & Mulaik 1936 and N. pearcei Gertsch 1941. Herein I review the genus which is now transferred from the Clubionidae to the Liocranidae, provide a distribution map and describe the females for the first time. Over 55% of the specimens of both species examined in this study came from the Nevada Test Site (i.e., atomic bombing range) in southern Nevada. Collection phenology at this site showed almost non-overlapping temporal activity for the males and habitats for each species within this area. Immatures from the Nevada Test Site also could be separated where the ventral anterior tibia spination and habitat dichotomy matched that of the adults. If this extrapolation holds throughout the distribution and there are no additional species, one should be able to accurately identify immatures of any size to species.
Keywords: Arachnida, taxonomy
ABSTRACT. Sybota atlantica new species is described from the Atlantic coast of Buenos Aires Province, Argentina. The morphology of genitalia and carapace suggests that the new species forms a monophyletic group with S. mendozae Opell 1979 and S. rana (Mello-Leitao 1941). The female genitalia of the genus shows an unusual grade of entelegyny, with copulatory and fertilization ducts leading to a common tube.
RESUMEN. Sybota atlantica nueva especie es descripta para la costa atlantica de la provincia de Buenos Aires, Argentina. La morfologia genital y cefalica sugiere que la nueva especie forma un grupo monofiletico con S. mendozae Opell 1979 y S. rana (Mello-Leitao 1941). Los organos genitales femeninos muestran un inusual grado de enteleginia, con los conductos de copulacion y fertilizacion convergiendo en un tubo comun.
Keywords: Uloboridae, Sybota, taxonomy, Argentina
by Akio Tanikawa
ABSTRACT. Several specimens of a unique spider were collected in Okinawajima Island, Southwestern Japan. They resemble the spiders of the genus Leucauge and its related genera. Phylogenetic analysis was performed to clarify the taxonomic position of the spider, which showed that the focal spider is a sister of a monophyletic group consisting of Tylorida and Mesida. Therefore it is described as a new genus and species under the name Okileucauge sasakii new species. This species lacks the rows of trichobothria on femur IV, which is the synapomorphy of the genera Tylorida and Mesida.
Keywords: Okileucauge sasakii,
new genus, new species, Tetragnathidae
de las especies de Freya del grupo decorata (Araneae, Salticidae)
by Maria Elana Galiano
ABSTRACT. Eight species of the genus Freya Koch 1846, closely related with the type species Freya decorata (Koch 1846), are revised and redescribed: F. decorata, F. regia (G. & E. Peckham 1896), F. maculatipes (Cambridge 1901), F. nigrotaeniata (Mello-Leit;tzao 1945) new combination, F. rubiginosa (Koch 1846), new combination. The female of F. nigrotaeniata is described for the first time. Three new species are described: F. dureti from Brazil, F. chapare from Bolivia and F. atures from Venezuela. Diagnostic characters for the genus are given.
RESUMEN. Ocho especies del genero Freya Koch 1846, estrechamente relacionadas con la especie tipo Freya decorata (Koch 1846), son revisadas y redescriptas: F. decorata (Koch 1846), F. regia (G. & E. Peckham 1896), F. maculatipes (Cambridge 1901), F. nigrotaeniata (Mello-Leit;tzao 1945) nueva combinacion y F. rubiginosa (Koch 1846) nueva combinacion. Las hembras de F. nigrotaeniata se describen por primera vez. Se describen tres especies nuevas: F. dureti de Brasil, F. chapare de Bolivia y F. atures de Venezuela. Se dan caracteres diagnosticos del genero.
Freya decorata group, Neotropica
ABSTRACT. A new species in the nitidulus group of Vaejovis is described: V. mauryi from Sonora, Mexico. Morphological characters, including the hemispermatophore of the holotype male, are illustrated. The species is compared to Vaejovis decipiens, Vaejovis janssi, and Vaejovis intermedius.
Keywords: Scorpion, Vaejovidae,
Sonora, Mexico, taxonomy
new species of Vaejovis (Scorpiones, Vaejovidae) from Sonora, Mexico
by Brent E. Hendrixson
ABSTRACT. Vaejovis pequeno, a new species of scorpion previously confused with V. waueri Gertsch & Soleglad 1972, is described and illustrated from Sonora, Mexico and is compared to that species. A revised diagnosis and new distributional records for V. waueri, a member of the eusthenura group, are provided.
Keywords: Scorpion, Vaejovidae,
Sonora, Mexico, systematics
influence of group size on dispersal in the social spider Stegodyphus mimosarum
by Marilyn Bodasing, Rob Slotow & Tanza Crouch
ABSTRACT.The costs and benefits of group living vary with group size, and competition for resources increases with increasing group size. In the social spider, Stegodyphus mimosarum individuals attain smaller sizes, and survival is lower in larger colonies. In this study we assess whether group size influences the decision to leave a colony or disperse. Four colony sizes (8, 16, 32 and 64) of S. mimosarum were set up under a proportional feeding regime in a laboratory experiment. We expected more spiders to leave large colonies due to intra-group competition. However, there was no significant increase in the number of spiders leaving with increasing group size. Significantly more spiders left a colony during spring and when spiders were larger (at a more advanced stage of development). Variability in access to resources does not promote dispersal, but season and spider size does influence dispersal.
Keywords: Group size, intragroup
competition, dispersal, social spiders, Stegodyphus mimosarum
ABSTRACT. On three separate occasions during the growth season four populations of the sheet web spider Linyphia triangularis were sampled, twice as immatures and once as adults. For the immature specimens, five linear size characteristics (length and width of the cephalothorax, length of tibia of the first leg, and length and height of the abdomen) were measured in the laboratory and compared with fresh weight. The best predictor of weight was abdomen length, closely followed by cephalothorax width. Cephalothorax width was used to compare the size of immatures with the adult size at time of maturity because the abdomen shrinks in the non-foraging adult males. Mean cephalothorax width was larger for males than for females in both immature and adult specimens. The difference increased from the earliest immature population samples to the adult samples. The relationship between cephalothorax width and abdomen length was linear and equal between the sexes over all immature samples. This means that there was no difference in the allocation of resources to body parts important to female fecundity (the abdomen) vs. body parts important to male fighting ability (the cephalothorax) between males and females. Selection for large male size thus seems to be greater than selection for large female size in this web-building spider, resulting in an overall faster growth rate in males. Males grow >10% larger than females despite the distinct protandry in this species.
Keywords: Sexual dimorphism,
Linyphia triangularis, growth rate, spider
ABSTRACT. The predatory habit of three species of sac spiders, Chiracanthium inclusum, Hibana velox, and Trachelas volutus, on citrus leafminer, Phyllocnistis citrella, was investigated. Observation of spider activities during the photophase and the scotophase confirmed that these three species of sac spiders are nocturnal. They detect their prey by sensing vibrations of the substrate induced by the concealed prey. Movements of P. citrella larvae and prepupae appear to create vibrations of the leaf substrate, which then serve as cues for the spiders to locate them. The searching and prey capture behaviors of these spiders are discussed. Two methods of prey attack were exhibited. In one method, the spider punctures the mine, immobilizes the larva and then bites it and sucks the larval body fluid. In the second behavioral pattern, the spider makes a slit in the mine, uses its forelegs to pull the larva or prepupa out of the mine, holds the prey securely, and finally bites it and regurgitates digestive juices into the prey and ingests the pre-digested liquid tissue. The three species of sac spiders were found to start feeding on P. citrella larvae during the 2nd instar stage. Consumption increased as they developed to later instars. Maximum consumption for all species was recorded at the 4th instar. Although C. inclusum and T. volutus can complete their life cycle with P. citrella as their only food, H. velox was not able to develop to the adult stage. Results obtained from this study provide useful data to better understand the role of sac spiders in the overall management of P. citrella.
prey capture, feeding stage, Phyllocnistis citrella, sac spiders
in the chemical composition of orb webs built by the spider Nephila clavipes
by Linden E. Higgins, Mark A. Townley, Edward K. Tillinghast & Mary Ann Rankin .
ABSTRACT. The adhesive droplets in the orb webs of araneoid spiders contain, among other constituents, an aqueous solution of organic low-molecular-weight compounds. The chemical composition of this solution has been investigated for pooled web collections from several species, but little is known about how the composition might vary among individuals or among environments. To begin addressing these questions, we analyzed serial collections of orb webs spun by individual juvenile Nephila clavipes from three different populations held first under field conditions and then under laboratory conditions. Our results indicate that the composition of the organic low-molecular-weight solution is not fixed. We found significant differences in the droplet composition among individuals, among populations, and with the transfer of spiders to laboratory conditions. The possible origins and consequences of these differences are discussed.
Keywords: Orb web chemistry,
interpopulational variation, intrapopulational variation, compatible solutes,
ABSTRACT. We studied spatial and temporal patterns of abundance of Ctenus amphora, C. crulsi, C. manauara and C. villasboasi, four syntopic species of medium-to-large sized wandering spiders that forage on the ground in a neotropical rainforest. We found temporal variation, apparently seasonal, in abundance for two of the four species. The four species are sympatric in the study area, but with very distinct spatial patterns of abundance. Ctenus amphora was more abundant in areas with sandy soil but are also common on clay soils, C. manauara and C. crulsi are the dominant species in areas with clay soil and are infrequent in sandy soils, and C. villasboasi had a more homogenous abundance in the study area. Previous studies suggested that a predator, army ants, could have an important impact on the abundance of these spiders. We estimated the frequency of attacks by army ants using pitfall traps in sandy and clay soil areas. The estimated probability of attack by army ants was higher in areas with clay soil (92% per 3 months), where all species are frequently found, than in sandy soil areas (21%), where C. crulsi and C. manauara were almost absent. However, it is still not clear if predation by army ants is a key factor that facilitates coexistence in clay soils, and this factor can not explain the difference on the dominant species between areas with different soil types. We also discuss the description of spatial patterns of abundance as a simple, but powerful, tool seldom used for preliminary studies on the coexistence of spiders.
RESUMO. Nos estudamos padroes espaciais e temporais de abundancia Ctenus amphora, C. crulsi, C. manauara e C. villasboasi, quatro especies sintopicas de aranhas errantes que forrageiam no chao em uma floresta neotropical umida. Nos encontramos uma variacao temporal, aparentemente sazonal, na abundafancia de duas das quatro especies. As quatro especies sao simpatricas na area de estudo, mas compadroes espaciais de abundancia muito distintos. Ctenus amphora foi mais abundante em areas de solos arenosos, mas tambem foi comum em solos argilosos C. manauara e e C. crulsi foram as especies dominantes em solos argilosos, e foram infreqentes em solos arenosos, e C. villasboasi teve uma abundancia mais homogenea na area de estudo. Estudos anteriores sugeriram que um predador, formigas de correico, poderia ter um forte impacto sobre a abundancia destas aranhas. Nos estimamos a frequencia de ataques por formigas de correicao usando armadilhas de fosso (pitfall traps) em areas de solo arenoso e argiloso. A probabilidade estimada de ataques por formigas de correicao foi maior em areas de solo argiloso (92% em 3 meses), onde todas as especies sao frequentemente encontradas, que em solo arenoso (21%), onde C. crulsi e C. manauara foram raras. Entretanto, ainda nao esta claro se a predacao e um fator chave para facilitar a coexistencia em solos argilosos, e este fator nao pode explicar a diferenca de especies dominantes entre as areas com tipos de solo diferentes. Nos tambem discutimos a descricao de padroes espaciais de abundancia como um ferramenta simples, mas poderosa e pouco usada para o estudo da coexistencia de aranhas.
Keywords: Army ants, predation,
change in coloration and web-building behavior in the tropical spider Eriophora
fulginea (Araneae, Araneidae)
by Barbara Graf & Wolfgang Nentwig
ABSTRACT. Eriophora fuliginea (Araneae, Araneidae), a tropical orb-weaving spider from Panama, undergoes a dramatic color change in the course of its ontogenesis. The first free instar has an amber opisthosoma, which soon becomes bright yellow, later green. Subadults change to olive, adults are dark brown with a white median stripe. Parallel to this color modification the spider's behavior changes as well. The main activity phase shifts from day to night and web architecture changes from symmetrical horizontal orb-webs on the upper side of leaves with the spider on the hub, to asymmetrical horizontal orb-webs between shrubs with spiders in a rolled leaf nearby.
Keywords: Ontogenetic change,
development, coloration, behavior, orb web
A spider family newly introduced to the USA (Araneae,Entelegynae, Lycosoidea)
by Charles E. Griswold & Darrell Ubick
ABSTRACT. The spider family Zoropsidae is newly recorded for the USA, bringing the total to 68 families. Zoropsis spinimana (Dufour 1820), native to the Mediterranean region, has been established in the San Francisco Bay area since at least 1995. The identification and phylogenetic position of this species are provided.
Keywords: Spiders, exotic,
introduction, Zoropsidae, Lycosoidea
of Stegodyphus dumicola (Araneae, Eresidae): They do balloon after all!
by Jutta M. Schneider, Jörg Roos, Yael Lubin and Johannes R. Henschel
ABSTRACT. There has been some controversy about whether adult females of social Stegodyphus disperse by ballooning. Here we show that adult Stegodyphus dumicola (Eresidae) Pocock 1898 are able to gain up-lift by releasing a very large number of threads. The threads fan out widely from the spider's body and form a triangular sheet. This previously unknown ballooning mechanism, enables even large spiders to disperse over large distances.
Keywords: Eresidae, Stegodyphus, dispersal, ballooning, social spider
ABSTRACT. A surgical technique for implanting passive integrated transponders into theraphosid spiders is described. An effecitve procedure for anesthesia was developed. Transponders were implanted in the opisthosomas of 12 spiders. No mortality occurred, and all spiders regained normal behavior. In simulated burrows, tarantulas could be identified to a depth of 16 cm.
Keywords: PIT tags, spider
ABSTRACT. A house spider (Tegenaria atrica C.L. Koch 1843, Agelenidae) was observed, filmed and photographed while feeding on an earthworm. An extensive search in the literature revealed that several arachnologists had noted spiders feeding on earthworms, altogether in 11 different families. Earthworm-eating spiders belong mostly to larger sized species dwelling near the ground in woodlands and grasslands. Since earthworms have a high protein content, they could be a welcome supplement to the spider's usual insect diet.
Keywords: Spiders, prey, foraging,
This page was posted 5 / 9 / 2001 and modified 11 / 27 / 2009