Alternative Reproductive Tactics in Spiders

The comparative study of reproduction at the level of populationand individual is a relatively recent development in spiderresearch. Such study is necessary to describe and examine alternativereproductive tactics. Female spider tactics are related to adaptationsfor a carnivorous mode of feeding. Being the larger of the sexes,the female has the alternative of mating with or preying uponattending males. In web building spiders, which are generallysolitary, other female alternatives are related to characteristicsof a web used in prey capture. These alternatives include differentresponses when defending the web, and individually buildingthe web so that it does or does not contact another. Tacticsmay vary in communal species which build a sheet-like structure,as females may remain in the colony or emigrate and establisha small web. Male spiders usually search for females, and matingoccurs on or near a female retreat or web. A male may show differentalternatives in mate searching, demonstrate various courtshipand copulatory tactics, copulate or feed on the female's preywhile she feeds, and guard the female after mating or departand search for another female. Certain characteristics of femalesare related to these male alternatives, these characteristicsbeing: larger size and longer life expectancy as compared withthe male, carnivorous feeding, and sexual receptivity. Maleweb spiders may also use alternatives while defending positionon the female web. These alternatives are related to the designand placement of the web, and occasional web abandonment bythe female. Relevant literature is reviewed and research suggested.     

Electric Fields Elicit Ballooning in Spiders

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Bat Predation by Spiders

In this paper more than 50 incidences of bats being captured by spiders are reviewed. Bat-catching spiders have been reported from virtually every continent with the exception of Antarctica (∼90% of the incidences occurring in the warmer areas of the globe between latitude 30° N and 30° S). Most reports refer to the Neotropics (42% of observed incidences), Asia (28.8%), and Australia-Papua New Guinea (13.5%). Bat-catching spiders belong to the mygalomorph family Theraphosidae and the araneomorph families Nephilidae, Araneidae, and Sparassidae. In addition to this, an attack attempt by a large araneomorph hunting spider of the family Pisauridae on an immature bat was witnessed. Eighty-eight percent of the reported incidences of bat catches were attributable to web-building spiders and 12% to hunting spiders. Large tropical orb-weavers of the genera Nephila and Eriophora in particular have been observed catching bats in their huge, strong orb-webs (of up to 1.5 m diameter). The majority of identifiable captured bats were small aerial insectivorous bats, belonging to the families Vespertilionidae (64%) and Emballonuridae (22%) and usually being among the most common bat species in their respective geographic area. While in some instances bats entangled in spider webs may have died of exhaustion, starvation, dehydration, and/or hyperthermia (i.e., non-predation death), there were numerous other instances where spiders were seen actively attacking, killing, and eating the captured bats (i.e., predation). This evidence suggests that spider predation on flying vertebrates is more widespread than previously assumed.     

Spiders in a Grape Vineyard in Korea

Survey was conducted to determine the composition of the spiders in a grape vineyard by using pitfall traps in Sunggeo-eup, Chunan in 1999. Total 17 genera and 19 species belonging to 10 families of spiders were identified. The dominant family was Linyphiidae. Overall, the seasonal fluctuation of the spider population showed two peaks a year. The results showed that the composition of species was very poor and occurrence density was very low in a grape vineyard in this study.     

Spiders as biological controllers in the agroecosystem

In this paper, we propose a general model consisting of insects, pests and spiders interacting in an agroecosystem included in a typical homogeneous rural landscape, characterized by a continuous mosaic of cultivated land and a few small patches of grasslands and small woods bounding the fields. The model is general enough to show all the phenomena observed in the agroecosystem. The role of the spider population as a biological controller in the agroecosystem is particularly emphasized. Human intervention by means of pesticide spraying and its relationship with the biological pest controllers is also accounted for.     

Control of Drag-Line Spinning in Certain Spiders

Araneomorph spiders from many different families show some regionaldifferentiation of the duct which carries the drag-line silk,but only in the orb-web spiders is there a well-defined controlvalve. This valve, and its associated muscles, is described for Araneusdiadematus (Argiopidae), an ecribellate spider, and is comparedwith that found in Uloborus octonarius (Uloboridae), a cribellatespider. It is suggested that the remarkable similarity betweenthe valves in these two groups implies evolutionary convergence. Some evidence is presented which suggests that variations inbody pressure are used to control the drag-line spinning, atleast in the more primitive Araneomorphs.     

Spiders spinning electrically charged nano-fibres

Most spider threads are on the micrometre and sub-micrometre scale. Yet, there are some spiders that spin true nano-scale fibres such as the cribellate orb spider, Uloborus plumipes. Here, we analyse the highly specialized capture silk-spinning system of this spider and compare it with the silk extrusion systems of the more standard spider dragline threads. The cribellar silk extrusion system consists of tiny, morphologically basic glands each terminating through exceptionally long and narrow ducts in uniquely shaped silk outlets. Depending on spider size, hundreds to thousands of these outlet spigots cover the cribellum, a phylogenetically ancient spinning plate. We present details on the unique functional design of the cribellate gland–duct–spigot system and discuss design requirements for its specialist fibrils. The spinning of fibres on the nano-scale seems to have been facilitated by the evolution of a highly specialist way of direct spinning, which differs from the aqua-melt silk extrusion set-up more typical for other spiders.     

Spiders fluoresce variably across many taxa

The evolution of fluorescence is largely unexplored, despite the newfound occurrence of this phenomenon in a variety of organisms. We document that spiders fluoresce under ultraviolet illumination, and find that the expression of this trait varies greatly among taxa in this species-rich group. All spiders we examined possess fluorophores in their haemolymph, but bright fluorescence appears to result when a spider sequesters fluorophores in its setae or cuticle. By sampling widely across spider taxa, we determine that fluorescent expression is labile and has evolved multiple times. Moreover, examination of the excitation and emission properties of extracted fluorophores reveals that spiders possess multiple fluorophores and that these differ among some families, indicating that novel fluorophores have evolved during spider diversification. Because many spiders fluoresce in wavelengths visible to their predators and prey (birds and insects), we propose that natural selection imposed by predator-prey interactions may drive the evolution of fluorescence in spiders.     

广西蜘蛛名录

本文报道广西蛛形纲Arachnida,蜘蛛目Araneae40科166属410种,并分别记述各种蜘蛛的地理分布和生境。     

Ontogeny of Web-building Behavior in Two Orb-weaving Spiders

Spideis of similar miss but of two different species Araneusdiadematus Cl. and Argiope aurantia L., build webs which havesimilar geometric patterns, but which differ in relative proportionsand thread number. Within species, webs may also differreliably,presumably on a genetic basis. Fine detail of the web undergoeschange throughout the lifetime of the spider, different formale and female; these changes are not simply response to thegrowing weight of the spider. Relatively simple restraints,such as availability of material for thread, result in adaptationsof web-building which may at first appear to be based upon buildingexperience, but which are in fact independent of it.     

Spiders and harvestmen as gastropod predators

1. Reports are reviewed of gastropod feeding (malacophagy) by spiders and harvestmen. Although the standard textbooks on arachnids recognise the importance of gastropods as prey of harvestmen, none apparently refers to malacophagy by spiders. A review of several hundred papers on spider feeding habits revealed that species from several families kill and devour slugs and snails in the laboratory and/or field. 2. Malacophagy has been reported most frequently among mygalomorph spiders, and can make up a substantial proportion of the diets of some species, however gastropods make up an insignificant percentage of the prey of most araneomorph spiders. The spiders that eat gastropods are species with broad diets composed predominantly of arthropod prey. No species of spider appears to feed exclusively on gastropod prey. 3. Harvestmen from several families have broad diets that often include gastropods. Several species of the family Trogulidae and at least one species of the family Ischyropsalididae [Ischyropsalis hellwigi (Panzer)] are specialised gastropod predators. The trogulids are slender animals that attack the snail through the shell aperture (shell intruders). Ischyropsalis hellwigi, on the other hand, can crush snail shells with its powerful chelicerae (shell breakers). 4. The review highlights apparent convergent evolution by harvestmen and Carabidae of two mutually exclusive morphologies found among gastropod predators. It also suggests that there is an urgent need for systematic studies to be conducted to establish the extent and ecological importance of malacophagy in natural and anthropogenically altered habitats.     

山西历山国家级自然保护区蜘蛛名录

在经过多年野外调查、采集、室内显微鉴定的基础上,本课题组将采自山西历山国家级自然保护区已定名的蜘蛛种类名录整理于下,共包括18科45属71种,其中包括2个大陆新记录种,1个山西新纪录科,9个山西新纪录属,26个山西新记录种.     

Web-Building Flexibility Differs in Two Spatially Constrained Orb Spiders

Shelter and trap-building animals that compete for limited space and/or face costly relocations benefit from being flexible in their construction behavior. Orb spiders are good examples of this and their easily quantifiable two-dimensional webs allow us to analyze the behavioral adaptations and costs in terms of higher error levels or less precision resulting from building webs in sub-optimal conditions. Here I study behavioral flexibility in spatially constrained spiders by analyzing a wide range of web parameters including measures that indicate errors during web-building. I compare the geometry of laboratory webs of two orb spiders, Cyclosa caroli and Eustala illicita, built in differently shaped experimental frames and report two major findings. i) The two species differ in their ability to build webs in constrained spaces. ii) E. illicita adjusted a range of parameters including shape, area utilization and mesh height in response to spatial constraints, but kept other parameters constant, most notably the length of anchor threads and the shape of the auxiliary spiral. I furthermore found that constrained spiders did not make significantly more errors during web-building than when they had amble space available.     

初冬季节的河北省棉田蜘蛛

利用陷阱法在1994年10月到11月间对河北省永年县棉田的蜘蛛进行了调查.共采集到8种蜘蛛,隶属于5科8属.对棉田蜘蛛的越冬蛛态、雌雄性比进行了研究.分析了越冬蛛态和雌雄性比对翌年蜘蛛种群发生的影响.