Abstracts to Articles

The Journal of Arachnology

Volume 28 Number 2

DESCRIPTION OF THE MALE OF SOSIPPUS PLACIDUS, WITH NOTES ON THE SUBFAMILY SOSIPPINAE (ARANEAE, LYCOSIDAE)

Petra Sierwald: Department of Zoology, Insects, Field Museum of Natural History,1400 South Lake Shore Drive, Chicago, Illinois 60605 USA

ABSTRACT. The male of the Florida funnel-web building wolf spider species Sosippus placidus Brady 1972 is described and figured for the first time. Analysis of the male palp's morphological structure reveals that Sosippus possesses a median apophysis like other members of the Araneoclada, but which of the three additional tegular apophyses is the conductor cannot be determined at present. The study demonstrates that the palea, the putative key apomorphy of the clade Venoniinae-Allocosinae-Pardosinae-Lycosinae requires further morphological analysis. The genus Porrimosa is a close relative of the genus Sosippus based on shared characters in the male palp. The ontogeny of the female copulatory organs of Sosippus agrees with that of other members in the RTA clade. Hippasella nitida Mello-Leitao 1944, placed by Capocasale (1990) in the genus Sosippus, is not recognized as a congener.

Keywords: Porrimosa, Iycosid subfamilies, male palp structure

The Journal of Arachnology 28:133-140

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IRACEMA CABOCLA NEW GENUS AND SPECIES OF A THERAPHOSID SPIDER FROM AMAZONIC BRAZIL (ARANEAE, THERAPHOSINAE)

Fernando Perez-Miles: Seccion Entomologfa, Facultad de Ciencias, Igua 4225, 11400 Montevideo, Uruguay

ABSTRACT. The new genus Iracema (Araneae, Theraphosidae, Theraphosinae) comprising the only species Iracema cabocla, from the Amazonic state of Roraima, Brazil, is described. The cladistic relationships of this genus within the Theraphosinae are analyzed.

Keywords: Theraphosid phylogeny, Amazonic spider, systematics

The Journal of Arachnology 28:141-148

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RESPIRATORY SYSTEM MORPHOLOGY AND THE PHYLOGENY OF HAPLOGYNE SPIDERS (ARANEAE, ARANEOMORPHAE)

Martin J. Ramirez: Laboratorio de Atropodos, FCEyN, Universidad de Buenos Aires, Pabellon II Ciudad Universitaria (1428), Buenos Aires, Argentina, and Museo Argentino de Ciencias Naturales, Av. Angel Gallardo 470 (1405), Buenos Aires, Argentina

ABSTRACT. The morphology of the respiratory system of basal araneomorph spiders, the Haplogynae and of Entelegynae with female haplogyne genitalia, is reviewed. The homology of cuticular respiratory structures is discussed in light of evidence from abdominal muscles and ontogeny. Ten morphological characters (13 transformations) were coded, mainly from the posterior pulmonary (or tracheal) segment, and other 7 non-respiratory characters here added. The new data were combined with those of a previously published analysis, resulting in a data matrix of 82 characters scored for 44 terminals. The evolution of the tracheal system is traced through the phylogeny of basal spiders and the Haplogynae, and new synapomorphies are provided. Elongate 3rd abdominal entapophyses are a synapomorphy of Araneomorphae. True median tracheae are a synapomorphy of Entelegynae (convergently with Austrochilinae), as is the extreme posterior displacement and narrowing of the tracheal spiracle. Tetrablemmidae, Pholcidae, Diguetidae and Plectreuridae are united by the absence of tracheae; and these taxa are united with Scytodidae, Sicariidae and Drymusidae by the fusion of 3rd entapophyses.

Keywords: Tracheae, cladistics, abdominal muscles

The Journal of Arachnology 28:149-157

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EFFECTS OF CLIMATE AND PREY AVAILABILITY ON FORAGING IN A SOCIAL SPIDER, STEGODYPHUS MIMOSARUM (ARANEAE, ERESIDAE)

T.E. Crouch: Department of Zoology and Entomology, University of Natal, Pietermaritzburg, South Africa and Durban Natural Science Museum, RO. Box 4085, Durban 4000, South Africa.
Y. Lubin: Mitrani Department of Desert Ecology, Blaustein Institute for Desert Research, Ben Gurion University of the Negev, Sede Boqer Campus, 84990 Israel

ABSTRACT. Tropical areas with favorable climatic conditions, high prey availability and large prey size are assumed to favor sociality in spiders. Notwithstanding, the three social species of Stegodyphus (Eresidae) inhabit arid and semi-arid habitats with marked daily and seasonal variation in climate. The nests of the social spider Stegodyphus mimosarum Pavesi commonly occur in dry Acacia savanna in southern Africa We investigated the abiotic conditions to which the nests of S mimosarum are exposed and the changes in availability of potential insect prey at different times of year and over the daily cycle. We used these data to determine the extent to which prey availability and climatic conditions explain seasonal and daily variation in the activity of the spiders Data were collected during four sampling periods a year over two years from nests of S. mimosarum located on the Mkomazi River Bridge (KwaZulu-Natal, South Africa). We measured ambient and nest temperatures and in a sample of nests, spider growth rate, prey availability, foraging activity and activity on the web at night. Spiders had two periods of increased growth rate occurring in early and late summer, at times of year when ambient temperature rarely falls below 20 °C. Temperatures inside the nest were generally higher than ambient throughout the day and night. Foraging response, measured as the numbers of individuals responding to the vibrations of a tuning fork, was significantly higher by night than by day. In summer, foraging response decreased with increasing temperature during the day, whereas in winter, there was a positive correlation between foraging response and temperature at night. Potential prey, measured as mean numbers of insects trapped in a sample of webs, were more abundant during the day than at night, despite the fact that the spiders were most active on the web at night. Nocturnal insects, however, were larger than diurnal ones and spiders handled significantly more large prey both during the day and at night. Correlation and partial correlation analyses indicate that ambient temperature and windspeed play a direct role in influencing foraging and other activity on the web. Nonetheless, the predominance of nocturnal activity in both summer and winter could not be explained by climatic conditions and prey availability alone. Some other factor (e.g., predation or parasitism) may be involved.

Keywords: Climate, prey availability, foraging, social spider

The Journal of Arachnology 28:158-168

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THE IMPACT OF HABITAT FEATURES ON WEB FEATURES AND PREY CAPTURE OF ARGIOPE AURANTIA (ARANEAE, ARANEIDAE)

C. Neal McReynolds: Natural Science Division, Blue Mountain College, Blue Mountain, Mississippi 38610 USA

ABSTRACT. Prey capture by the orb-web spider, Argiope aurantia Lucas 1833, depends on the type of the web-site selected. I analyzed A. aurantia web sites in open field and adjacent forest edge habitats to identify habitat features associated with web characteristics and prey capture. In the open field, the use of herbs or grass for web attachment was associated with smaller web diameters, and lower attachment heights and web heights. In both forest edge and open field, the distance to the nearest flower was less when web attachments were on composites. In the open field, webs attached to grass captured more orthopteran prey, and webs attached to herbs and composites captured more hymenopteran prey. The mean number of prey captured and the proportion of hymenopteran prey increased with higher web attachments in the open field habitat. Close proximity of webs to goldenrod in bloom in the open field habitat increased the mean number of prey captured and the proportion of hymenopteran prey. In the forest edge habitat, the presence of goldenrod was associated with more hymenopteran and orthopteran prey and with a higher mean prey number captured. Generally, webs in the open field habitat had more hymenopteran and orthopteran prey and higher mean prey number captured than the forest edge habitat. The web-site providing the greatest probability for encountering and capturing prey is predicted to be one with a tall composite plant for web attachment near goldenrod in bloom.

Keywords: Habitat selection, old-field habitat, predation, web-site

The Journal of Arachnology 28:169 - 179

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EVALUATION OF FORMULAE TO ESTIMATE THE CAPTURE AREA AND MESH HEIGHT OF ORB WEBS (ARANEOIDEA, ARANEAE)

Marie Elisabeth Herberstein: Department of Zoology, University of Melbourne, Parkville 3010, Australia
I-Min Tso: Department of Biology, Tunghai University, Taichung 407, Taiwan

 

ABSTRACT. We evaluated several formulae to estimate the capture area (the area of the web covered by capture spirals) and the mesh height (the distance between capture spirals) of orb webs constructed by Argiope keyserlingi Karsch. The accuracy of the various formulae was estimated through regression analyses. Accordingly, we propose two new formulae specifically suited for asymmetric orb webs, which provide accurate estimates of capture area and mesh height.

Keywords: Web architecture, web design, Araneidae, Argiope keyserlingi

The Journal of Arachnology 28:180-184

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POPULATION STRUCTURE, SEASONALITY, AND HABITAT USE BY THE GREEN LYNX SPIDER PEUCETIA VIRIDANS (OXYOPIDAE) INHABITING CNlDOSCOLUS ACONlTlFOLl US (EUPHORBIACEAE)

Angelica M. Arango and Victor Rico-Gray: Departamento de Ecologia Vegetal, Instituto de Ecologfa, A.C.; Apdo. 63; Xalapa, VER 91000 Mexico
Victor Parra-Tabla: Departamento de Ecologfa, F.M.V.Z. Universidad Authnoma de Yucatan; Apdo. 4-116; Merida (Itzimna) YUC 97000 Mexico

ABSTRACT. For one year we studied the habitat use of Peucetia viridans living on Cnidoscolus aconitifolius, in a pasture land in Merida, Yucatan, Mexico Highest spider density was recorded in August (total 118, adults 77), and lowest in May (total 7, adults 2). Spider density was significantly higher in isolated plants and lower in plants in a patch. Sex ratio (male to female) varied from 1:1.5 in April, to 1:1 in May, and to 1:0.1 in September The dominant instar (both sexes) changed during the study. Throughout the study more spiders were recorded in 'repose' than performing any other activity. Foraging and feeding were more intense between July and September, when their prey, flower visitors, were more abundant. The number of spiders on plants varied spatially and temporally due to the combined effects of distance of the individual plant to the nearby forest, monthly precipitation, plant height, and number of panicles in anthesis. Forty-eight percent of the spiders were found living on plants with 20-30 panicles in anthesis (2% of the plant population). Most of the spiders (except for adult females) were found either below or above leaves. There were no significant differences in the distribution of most stadia respective to plant height. Positive significant correlations were found between the number of spiders and the abundance of floral visitors when the data were compared shifted-back one month, and between the number of spiders and the number of panicles in bloom when the data were compared shifted-back two months. When the abundance of spiders, floral visitors and number of panicles in bloom were correlated to monthly precipitation, we found a positive significant correlation for spider abundance when the data were compared shifted-back three months, a significant negative correlation for floral visitors when the data were compared shifted-back two months, and a nonsignificant correlation for the number of panicles in bloom, although both (panicles and floral visitors) peaked in May.

Keywords: Peucetia viridans, Cnidoscolus aconitifolius, population structure, seasonality

The Journal of Arachnology 28:185-194

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FOOD CONSUMPTION RATES AND COMPETITION IN A COMMUNALLY FEEDING SOCIAL SPIDER, STEGODYPHUS DUMICOLA (ERESIDAE)

Nava Amir, Mary E. A. Whitehouse and Yael Lubin: Mitrani Department of Desert Ecology, Blaustein Institute for Desert Research, Ben Gurion University of the Negev, 84990 Sede Boker, Israel

ABSTRACT. A major factor which affects an animal's consumption rate is competition for food items. Competition usually results in a drop in consumption rate; however, this may be counteracted if the animals can exploit the foraging efforts of others, as could occur in social spiders when feeding on the same prey item. Spiders digest prey extra-orally and might utilize the enzymes or digesta produced by other individuals feeding from the same prey item. We investigated prey consumption in the social spider Stegodyphus dumicola to determine if the rate of consumption of individual spiders changed in the presence of competitors. We found that when one spider fed on small prey, food consumption rate decreased with feeding duration. When the prey was larger in relation to the spider there was an initial delay in consumption. There was no apparent advantage for a second spider to feed on a prey item already being consumed: the second spider fed for less time and gained less mass. These results indicate that social spiders compete during the process of food ingestion and the presence of another spider reduces the value of the prey item to a subsequent forager.

Keywords: Competition, sociality, foraging

The Journal of Arachnology 28:195-200

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PREDATOR AVOIDANCE ON THE WATER SURFACE? KINEMATICS AND EFFICACY OF VERTICAL JUMPING BY DOLOMEDES (ARANEAE, PISAURIDAE)

Robert B. Suter and Jessica Gruenwald: Department of Biology, Vassar College, Poughkeepsie, New York 12604 USA

ABSTRACT. Vertical jumps of fishing spiders (Dolomedes sp.) from the water surface have been presumed to be evasive behaviors directed against predatory fish. We used high-speed videography to analyze the jumps of fishing spiders and then constructed a numerical model to assess the effectiveness of these jumps in evading predatory strikes by trout. Jump height (mean = 3.7 cm) and duration (mean = 0.17 sec) were similar across spider masses (0.05-0.66 g) but latency to jump increased significantly with mass. To accomplish jumps of similar height, more massive spiders had to generate more force during the propulsive phase of the jump than did smaller spiders; and the contribution of fluid drag to the total force used in jumping was substantially greater for large spiders than for smaller ones. Our model juxtaposing the jumps of spiders and the attacks of trout revealed that jump heights and durations were inadequate: only the most lethargic strikes by trout could be successfully evaded by jumping vertically from the water surface.

Keywords: Hydrodynamics, aquatic locomotion, predation, spider, Dolomedes

The Journal of Arachnology 28:201-210

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PREDATORY INTERACTIONS BETWEEN MUD-DAUBER WASPS (HYMENOPTERA, SPHECIDAE) AND ARG1OPE (ARANEAE, ARANEIDAE) IN CAPTIVITY

Todd A. Blackledge and Kurt M. Pickett: Department of Entomology, The Ohio State University, 1735 Neil Avenue, Columbus, Ohio 43210 USA

ABSTRACT. We report on efforts to maintain two common sphecid wasps, Chalybion caeruleum (Saussure 1867) and Sceliphron caementarium (Drury 1773), in field and laboratory enclosures in order to observe their predatory interactions with the orb-weaving spiders Argiope aurantia Lucas 1833 and A. trifasciata (Forskal 1775). Both species of wasps seemed to locate webs primarily by chance while flying along the tops of the vegetation but differed greatly in their hunting tactics once webs were located. Sceliphron caementarium was most successful at capturing spiders that had dropped out of webs in response to the wasp's hitting the web. But, C. caeruleum often employed a type of aggressive mimicry: it landed in the web or used its middle legs to pluck the web, luring the spider to the wasp. Argiope did not differ in their defensive response to C. caeruleum and S caementarium. Most Argiope dropped out of webs in response to attacks rather than using other defensive behaviors such as shuttling between sides of webs or vibrating webs.

Keywords: Sympatry, competition, niche partitioning

The Journal of Arachnology 28:211-216

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SPIDERS IN ROCKY HABITATS IN CENTRAL BOHEMIA

Vlastimil Ruzicka: Institute of Entomology, Czech Academy of Sciences, Branisovska 31, 370 05 Ceske Budejovice, Czech Republic

ABSTRACT. Spiders of andezite and limestone rocks in Central Bohemia were studied. The material was collected using hanging desk traps. Rocky habitats are inhabited by a well-established spider assemblage. A lower slope angle, and consequently more diverse terrain, probably support a higher species diversity. Some species inhabit exclusively rocky habitats. Segestria bovarica and Theridion betteni occur in the Czech Republic exclusively on rocky habitats. Erigonoplus jarmilae, Zelotes puritanus, and Altella binucata appear to occur primarily on rocky habitats. Anyphacna furva appears to live on trunks of trees growing on sun-exposed rocks. Some thermophilous species narrow their ecological niche exclusively to southern exposed rocky habitats with a warm microclimate towards the north.

Keywords: Spiders, rocks, vegetation-free habitats, thermophilous species

The Journal of Arachnology 28:217-222

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This page was posted 12 / 21 / 2000 and modified 11 / 27 / 2009