Higher-level phylogenetics of linyphiid spiders (Araneae, Linyphiidae) based on morphological and molecular evidence

This study infers the higher-level cladistic relationships of linyphiid spiders from five genes (mitochondrial CO1, 16S; nuclear 28S, 18S, histone H3) and morphological data. In total, the character matrix includes 47 taxa: 35 linyphiids representing the currently used subfamilies of Linyphiidae (Stemonyphantinae, Mynogleninae, Erigoninae, and Linyphiinae (Micronetini plus Linyphiini)) and 12 outgroup species representing nine araneoid families (Pimoidae, Theridiidae, Nesticidae, Synotaxidae, Cyatholipidae, Mysmenidae, Theridiosomatidae, Tetragnathidae, and Araneidae). The morphological characters include those used in recent studies of linyphiid phylogenetics, covering both genitalic and somatic morphology. Different sequence alignments and analytical methods produce different cladistic hypotheses. Lack of congruence among different analyses is, in part, due to the shifting placement of Labulla , Pityohyphantes , Notholepthyphantes , and Pocobletus . Almost all combined analyses agree on the monophyly of linyphioids, Pimoidae, Linyphiidae, Erigoninae, Mynogleninae, as well as Stemonyphantes as a basal lineage within Linyphiidae. Our results suggest independent origins of the desmitracheate tracheal system in micronetines and erigonines, and that erigonines were primitively haplotracheate. Cephalothoracic glandular specializations of erigonines and mynoglenines apparently evolved independently. Subocular sulci of mynoglenines and lateral sulci (e.g. Bathyphantes ) evolved independently but glandular pores in the prosoma proliferated once. The contribution of different character partitions and their sensitivity to changes in traditional analytical parameters is explored and quantified.
 © The Willi Hennig Society 2009.     

Rounding up the usual suspects: a standard target‐gene approach for resolving the interfamilial phylogenetic relationships of ecribellate orb‐weaving spiders with a new family‐rank classification (Araneae,Araneoidea)

We test the limits of the spider superfamily Araneoidea and reconstruct its interfamilial relationships using standard molecular markers. The taxon sample (363 terminals) comprises for the first time representatives of all araneoid families, including the first molecular data of the family Synaphridae. We use the resulting phylogenetic framework to study web evolution in araneoids. Araneoidea is monophyletic and sister to Nicodamoidea rank. n. Orbiculariae are not monophyletic and also include the RTA clade, Oecobiidae and Hersiliidae. Deinopoidea is paraphyletic with respect to a lineage that includes the RTA clade, Hersiliidae and Oecobiidae. The cribellate orb‐weaving family Uloboridae is monophyletic and is sister group to a lineage that includes the RTA Clade, Hersiliidae and Oecobiidae. The monophyly of most Araneoidea families is well supported, with a few exceptions. Anapidae includes holarchaeids but the family remains diphyletic even if Holarchaea is considered an anapid. The orb‐web is ancient, having evolved by the early Jurassic; a single origin of the orb with multiple “losses” is implied by our analyses. By the late Jurassic, the orb‐web had already been transformed into different architectures, but the ancestors of the RTA clade probably built orb‐webs. We also find further support for a single origin of the cribellum and multiple independent losses. The following taxonomic and nomenclatural changes are proposed: the cribellate and ecribellate nicodamids are grouped in the superfamily Nicodamoidea rank n. (Megadictynidae rank res. and Nicodamidae stat. n. ). Araneoidea includes 17 families with the following changes: Araneidae is re‐circumscribed to include nephilines , Nephilinae rank res., Arkyidae rank n. , Physoglenidae rank n. , Synotaxidae is limited to the genus Synotaxus, Pararchaeidae is a junior synonym of Malkaridae ( syn. n. ), Holarchaeidae of Anapidae ( syn. n. ) and Sinopimoidae of Linyphiidae ( syn. n. ).     

Phylogeny of extant nephilid orb-weaving spiders (Araneae, Nephilidae): testing morphological and ethological homologies

The Pantropical spider clade Nephilidae is famous for its extreme sexual size dimorphism, for constructing the largest orb-webs known, and for unusual sexual behaviors, which include emasculation and extreme polygamy. We synthesize the available data for the genera Nephila , Nephilengys , Herennia and Clitaetra to produce the first species level phylogeny of the family. We score 231 characters (197 morphological, 34 behavioral) for 61 taxa: 32 of the 37 known nephilid species plus two Phonognatha and one Deliochus species, 10 tetragnathid outgroups, nine araneids, and one genus each of Nesticidae, Theridiidae, Theridiosomatidae, Linyphiidae, Pimoidae, Uloboridae and Deinopidae. Four most parsimonious trees resulted, among which successive weighting preferred one ingroup topology. Neither an analysis of an alternative data set based on different morphological interpretations, nor separate analyses of morphology and behavior are superior to the total evidence analysis, which we therefore propose as the working hypothesis of nephilid relationships, and the basis for classification. Ingroup generic relationships are ( Clitaetra ( Herennia ( Nephila , Nephilengys ))) . Deliochus and Phonognatha group with Araneidae rather than Nephilidae. Nephilidae is sister to all other araneoids ( contra most recent literature). Ethological data, although difficult to obtain and thus frequently missing for rare taxa, are phylogenetically informative. We explore the evolution of selected morphological and behavioral characters, discuss and redefine the homology of palpal sclerites, disprove semientelegyny in spiders, trace the newly interpreted evolution of the orb web, and show that nephilid genital morphologies coevolve with sexual behaviors and extreme sexual size dimorphism. Phylogenetic interpretations of behavior suggest new insights into spider biology and avenues for future research.
© The Willi Hennig Society 2007.     

园蛛总科网型不同的蜘蛛间分子系统发生关系的初步探讨

为初步探讨园蛛总科内网型不同的蜘蛛间分子系统发生关系,测定了9种蜘蛛核18S rRNA基因的部分序列。联合GenBank中的2种蜘蛛18S rRNA基因序列数据,用NJ法、MP法和ML法重建分子系统树,结果表明：（1）织圆网的园蛛科和肖蛸科蜘蛛在园蛛总科中不是姊妹群;（2）不织圆网的球蛛科和皿蛛科也不是单系发生,证实了皿蛛片网和球蛛网独立起源的观点;（3）皿蛛科蜘蛛的分子系统发生地位与肖蛸科较近、而与园蛛科较远,这表明皿蛛科和园蛛科问雄性触肢结构的相似性很可能是类似而不是同源相似。     

Phylogenetic placement of the Tasmanian spider Acrobleps hygrophilus (Araneae, Anapidae) with comments on the evolution of the capture web in Araneoidea

This paper studies the family‐level phylogenetic placement of the conflicting Tasmanian spider genus Acrobleps using both morphological and behavioral data. We also provide a formal taxonomic revision of Acrobleps, including information on its web architecture and natural history, as well as detailed morphological information for A. hygrophilus, its only species. Acrobleps hygrophilus lacks the typical mysmenid features. Furthermore A. hygrophilus does have all typical and diagnostic characteristics of Anapidae, except for the labral spur. We also discuss two noteworthy morphological features of Acrobleps: the pore bearing depressions of the carapace and the granulated cuticle of the spinnerets. Variation in the latter feature might provide a useful phylogenetic character. Based on the results of cladistic analyses we propose the transfer of Acrobleps from the Mysmenidae to its original placement within the Anapidae. We also propose a new lineage, informally labeled as the “clawless female clade”, which includes synaphrids, cyatholipids and “symphytognathoids.” The secondary absence of the female palpal claw provides support for the “clawless female clade.” We discuss the evolution of the orb web within anapids and other symphytognathoids based on the results of our cladistic analyses. The identical bi‐dimensional webs of the anapid Elanapis and of symphytognathids have evolved independently. Finally, we comment on the implications of one of our analyses regarding araneoid web evolution. We conclude that the taxon sample included in the previous orbicularian data matrix (modified and used in this study) is adequate to test the phylogenetic placement of Acrobleps in Anapidae but insufficient to significantly assess web evolution within Araneoidea. © The Willi Hennig Society 2007.     

Diversity of insects captured by weaver spiders (Arachnida: Araneae) in the cocoa agroecosystem in Tabasco, Mexico

The aim of this work was to know the diversity of insects captured by weaver spiders in a plantation of cocoa (Theobroma cacao L.) of 6 ha in the State of Tabasco, Mexico. The study was carried out from July 2004 to June 2005 by means biweekly samples of the insects captured on the spiders webs. The total of 3,041 webs of 54 species of spiders belonging to seven families (Araneidae, Theridiidae, Tetragnathidae, Uloboridae, Pholcidae, Dyctinidae and Linyphiidae) were revised. We found 1,749 specimens belonging to 10 orders of insects, represented by 93 families, the majority of Coleoptera, Diptera and Hemiptera that constituted 74% of the identified families. The biggest number of specimens of all orders was captured by Araneidae, except of Isoptera, whose specimens were captured mainly by the family Theridiidae. The index of diversity (H'), evenness (J') and similarity (Is), applied to know the diversity of families of insects captured among families of spiders, varied from 0.00 to 3.24, 0.00 to 0.81, and 0.04 to 0.522, respectively. We conclude that there is a wide diversity of insects predated by the weaver spiders in the cocoa agroecosystem, and that there are species that can be promising for the biological control of pests.     

Cladistics and the comparative morphology of linyphiid spiders and their relatives (Araneae, Araneoidea, Linyphiidae)

This paper provides the first quantitative cladistic analysis of linyphiid morphology. Classical and novel homology hypotheses for a variety of character systems (male and female genitalia, somatic morphology, spinneret silk spigot morphology, etc.) are critically examined and studied within a phylogenetic context. Critical characters have been illustrated. A sample of linyphiid taxa (nine genera in four subfamilies), five species of Pimoa (Pimoidae), and two other araneoid families (Tetragnathidae and Araneidae, represented by Tetragnatha and Zygiella , respectively) were used to study the implications of the phylogeny of Pimoidae for the systematics of linyphiids. The phylogenetic relationships of these 16 exemplar taxa, as coded for the 47 characters studied, were analysed using numerical cladistic methods. In the preferred cladogram Pimoidae and Linyphiidae are sister groups, Stemonyphantinae are sister group to the remaining linyphiids, and Mynogleninae are sister group to the clade composed of Erigoninae plus Linyphiinae. These results agree with the relationships recently proposed by Wunderlich, except by finding erigonines as the sister group to linyphiines rather than to mynoglenines.     

How to catch foliage-dwelling spiders (Araneae) in maize fields and their margins: a comparison of two sampling methods

The foliage‐dwelling spider fauna was collected in maize fields and on stinging nettles in adjacent margins in Bavaria, South Germany. Two different sampling methods were evaluated: drop cloth sampling and suction sampling. The overall catch was dominated by juvenile spiders, web‐building spiders, and spiders of the families Theridiidae, Linyphiidae, Tetragnathidae and Araneidae (in decreasing order). Field margins harboured more species than maize fields, whereas the total spider abundance was higher in the maize crop. Web‐building spiders such as Theridiidae and Linyphiidae were prominent in maize by individual numbers. Suction sampling with a small suction device proved to be a more efficient and consistent sampling method for foliage‐dwelling spiders than drop cloth sampling. Density and species richness of foliage‐dwelling spiders in maize was shown to be fairly high, implying that spiders of higher strata may play a more important role in biological control than suspected up to now.     

A phylogenetic analysis of the orb-weaving spider family Araneidae (Arachnida, Araneae)

We present the first cladistic analysis focused at the tribal and subfamily level of the orb-weaving spider family Araneidae. The data matrix of 82 characters scored for 57 arancid genera of 6 subfamilies and 19 tribes (and 13 genera from 8 outgroup families) resulted in 16 slightly different, most parsimonious trees. Successive weighting corroborated 62 of the 66 informative nodes on these cladograms; one is recommended as the 'working' araneid phylogcny. The sister group of Araneidae is all other Araneoidea. Araneidae comprises two major clades: the subfamily Araneinae, and the 'argiopoid' clade, which includes all other subfamilies and most tribes (((Gasteracanthinae, Caerostreae), (((Micratheninae, Xylcthreae), Eruyosaccus ), (Eurycorminae, Arciinae)), Cyrlarachninae), ((Argiopinae, Cyrtophorinae), Arachnureae)). Cyrtarachneae and Mastophoreae are united in a new subfamily, Cyr-tarachninae. The spiny orb-weavers alone (Gasteracanthinae and Micratheninae) are not monophyletic. The mimetid subfamily Arciinae and the 'tetragnathid' genus Zygiella are araneids, but .Nephila (and other tetragnathids) are not. On the preferred tree, web decorations (stabilimenta) evolved 9 times within 15 genera, and were lost once. The use of silk to subdue prey evolved once in cribellate and four times in ecribillate orb weavers. Sexual size dimorphism evolved once in nephilines, twice in araneids, and reverted to monomorphism five times. Evolution in other genitalic and somatic characters is also assessed; behavioral and spinneret features arc most consistent (male genitalia, leg and prosomal features least consistent) on the phylogeny.     

Arboreal spiders in eastern hemlock

Eastern hemlock [Tsuga canadensis (L.) Carrière] is a foundation species in forests of eastern North America that plays a key role in ecosystem function. It is highly susceptible to the exotic invasive hemlock woolly adelgid (Adelges tsugae Annand), which is causing widespread hemlock mortality. We surveyed the spider communities of eastern hemlock and deciduous canopies over 2 yr, collecting over 4,000 spiders from 21 families. We found that eastern hemlock canopies harbored a more abundant, rich, and diverse spider community than did deciduous canopies. Five spider families were present in our hemlock collections that were absent from the deciduous collections, including Mysmenidae, Theridiosomatidae, Mimetidae, Lycosidae, and Agelenidae. In hemlock canopies there were 4× the number of web builders, consisting primarily of the Tetragnathidae and Araneidae, than active hunters, consisting primarily of the Anyphaenidae and the Salticidae. Ours is the first in depth study of the spider community in eastern hemlock. Spider abundance in hemlock canopies suggest that they may play a role regulating herbivore populations, and could possibly affect the invasive hemlock woolly adelgid, either through direct consumption of the adelgids themselves or through interactions with classical biological control agents.     

Advances in the Taxonomy of Spiders in Miocene Amber from the Dominican Republic (Arthropoda: Araneae)

Trachelas poinari sp. nov. (Corinnidae), Miagrammopes sp. indet. (Uloboridae) and the first indisputable fossil Lycosidae (gen. et sp. indet.) are newly identified and described in Miocene amber from the Dominican Republic. The following are junior synonyms: Nops segmentatus Wunderlich, 1988 of N. lobatus Wunderlich, 1988 (Caponiidae); Azilia muellenmeisteri Wunderlich, 1988 of A. hispaniolensis Wunderlich, 1988 (Tetragnathidae); and Lyssomanes galianoae Reiskind, 1989 of L. pristinus Wunderlich, 1986 (Salticidae). The specimens described as Nops sp. (Caponiidae), Selenops beynai Schawaller, 1984, S. sp. 1, and S. sp. 2 (Selenopidae) by Wunderlich (1988) are unrecognizable as distinct species. The following new combinations are presented: gen. indet. clypeatus (Wunderlich, 1988) (= Anelosimus clypeatus ) (Theridiidae); Meioneta bigibber (Wunderlich, 1988) (= Agyneta bigibber ), M. fastigata (Wunderlich, 1988) (= Agyneta fastigata ), M. separata (Wunderlich, 1988) (= Agyneta separata ) (Linyphiidae); Enacrosoma verrucosa (Wunderlich, 1988) (= Cyclosa verrucosa ) (Araneidae); Pseudosparianthis pfeiferi (Wunderlich, 1988) (= Tentabunda pfeiferi ) (Sparassidae). Theridion wunderlichi nom. nov. is proposed as a replacement name for T. ovale Wunderlich, 1988 (nom. preocc.). The previously unknown male of Styposis pholcoides Wunderlich, 1988 (Theridiidae) is described. Additional features of Argyrodes crassipatellaris Wunderlich, 1988 (Theridiidae) are described; this species is transferred from the trigonum to the cancellatus species group. Nine specimens belonging to six previously described species, and six juvenile Selenops sp. (including one exuvium) are newly identified. These are the first fossil records of Trachelas, Enacrosoma and Pseudosparianthis, giving them stratigraphic ranges of 15–20 my; the genera Anelosimus, Cyclosa and Agyneta are unknown in the fossil record.     

Phylogenetic relationships of the spider family Tetragnathidae (Araneae, Araneoidea) based on morphological and DNA sequence data

The monophyly of Tetragnathidae including the species composition of the family (e.g., Are Nephila and their relatives part of this lineage?), the phylogenetic relationships of its various lineages, and the exact placement of Tetragnathidae within Araneoidea have been three recalcitrant problems in spider systematics. Most studies on tetragnathid phylogeny have focused on morphological and behavioral data, but little molecular work has been published to date. To address these issues we combine previous morphological and behavioral data with novel molecular data including nuclear ribosomal RNA genes 18S and 28S, mitochondrial ribosomal RNA genes 12S and 16S and protein‐coding genes from the mitochondrion [cytochrome c oxidase subunit I (COI)] and from the nucleus (histone H3), totaling ca. 6.3 kb of sequence data per taxon. These data were analyzed using direct optimization and static homology using both parsimony and Bayesian methods. Our results indicate monophyly of Tetragnathidae, Tetragnathinae, Leucauginae, the “Nanometa clade” and the subfamily Metainae, which, with the exception of the later subfamily, received high nodal support. Morphological synapomorphies that support these clades are also discussed. The position of tetragnathids with respect to the rest of the araneoid spiders remains largely unresolved but tetragnathids and nephilids were never recovered as sister taxa. The combined dataset suggests that Nephilidae is sister to Araneidae; furthermore, the sister group of Nephila is the clade composed by Herennia plus Nephilengys and this pattern has clear implications for understanding the comparative biology of the group. Tetragnathidae is most likely sister to some members of the “reduced piriform clade” and nephilids constitute the most‐basal lineage of araneids.     

Nanoa, an enigmatic new genus of pimoid spiders from western North America (Pimoidae, Araneae)

The spider genus Nanoa gen. nov. (Araneae, Pimoidae) is described to place Nanoa enana , a new species of pimoids from Western North America. Parsimony analysis of morphological characters provides support for the monophyly of Pimoa plus Nanoa and corroborates the monophyly of Pimoidae and of the clade Linyphiidae plus Pimoidae. © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 145 , 249–262.     

2种不同采样方法对麦田蜘蛛群落结构的比较研究

分别于1998年11月到1999年5月和1999年11月到2000年5月间,在位于武汉市武昌区的沙湖边,使用样方和陷阱法系统采样,研究了裸粒大麦田的蜘蛛群落结构。研究结果显示,1998-1999年麦田蜘蛛群落由11科44种蜘蛛组成,1999-2000年麦田蜘蛛群落由14科59种蜘蛛组成;相同年份不同采样方法获得的蜘蛛群落优势种组成不同,陷阱法采样获得的优势种集中在皿蛛科、狼蛛科和平腹蛛科,而样方采样虽然也以皿蛛科和狼蛛科蜘蛛为主,但球蛛科、肖蛸科和园蛛科蜘蛛的比例明显上升;不同的年份使用相同的采样方法获得的蜘蛛优势种组成不同,显示了群落结构的年际变动。对2种采样方法获得的群落相似性分析显示,不同采样方法获得的群落结构相似性较小。     

Morphological phylogeny of cobweb spiders and their relatives (Araneae, Araneoidea, Theridiidae)

This paper offers the first cladistic analysis of a wide selection of theridiid genera based on morphological data. The analysis treats 53 theridiid taxa representing 32 genera (Achaearanea, Anelosimus, Ameridion, Argyrodes, Ariamnes, Carniella, Cerocida, Chrysso, Coleosoma, Dipoena, Emertonella, Enoplognatha, Episinus, Euryopis, Faiditus, Kochiura, Latrodectus, Neospintharus, Nesticodes, Pholcomma, Phoroncidia, Rhomphaea, Robertus, Selkirkiella, Spintharus, Steatoda, Stemmops, Theridion, Theridula, Thymoites, Thwaitesia, Tidarren) and eight outgroup taxa representing the families Nesticidae (Eidmanella and Nesticus), Synotaxidae (Synotaxus, two species), Pimoidae (Pimoa), Linyphiidae (Linyphia), Tetragnathidae (Tetragnatha) and Araneidae (Argiope). The parsimony analysis of 242 morphological and behavioural characters found a single, most parsimonious tree. The monophyly of theridiids and their sister relationship with nesticids is strongly supported. The recent resurrection of Ariamnes and Rhomphaea from Argyrodes made the latter paraphyletic. However, Ariamnes and Rhomphaea are characterized by an array of characters, and Argyrodes still contains dramatically distinct clades for which names are available: Faiditus (removed from synonymy ? RS) and Neospintharus (RS). These revalidations provide a classification with greater information content and utility. These three genera, along with Ariamnes, Rhomphaea and Spheropistha, comprise the subfamily Argyrodinae. The monophyly and composition of the subfamilies Hadrotarsinae, Spintharinae, Pholcommatinae, Latrodectinae and Theridiinae are discussed. Theridion is paraphyletic and in need of revision. Anelosimus as currently circumscribed is paraphyletic, a problem resolved by revalidating Selkirkiella (RS) and Kochiura (RS). Numerous new combinations are established. The results suggest the monophyletic origin of both kleptoparasitism and araneophagy in the lineage leading to Argyrodinae, negating hypotheses that either arose from the other. Sociality evolved multiple times within the family, accounting for as much as one fourth of the origins of social behaviour among all spiders. No losses of sociality are implied. The hypothesis of maternal care as the pathway to sociality receives support. Evolution of theridiid webs is complex, with multiple modifications and loss of the basic theridiid cobweb. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 141 , 447–626.     

Untangling the Tangle-Web: Web Construction Behavior of the Comb-Footed Spider Steatoda triangulosa and Comments on Phylogenetic Implications (Araneae: Theridiidae)

Theridiidae typically construct a three-dimensional web often described as irregular. The web consists of a supporting structure and lines under tension termed gumfooted lines. We used automated methods to observe web construction in the theridiid Steatoda triangulosa under laboratory conditions. Web construction lasted several nights. After orientation, spiders built a three-dimensional structure of several threads radiating sideways and downward from the retreat. To build gumfooted lines, they started from the retreat, moved along a structural thread, then dropped down to attach the thread to the lower substrate. On returning, they coated the lowest part of the thread with viscid silk before moving up along the same thread back to the structural thread. They then continued moving along the same structural thread to drop down again to build the next gumfooted line. This behavior was continued until the spiders had built a series of gumfooted lines (a bout). There were regular intervals between the construction of two bouts. Thus, a single web included many bouts built in different stages. We show that gumfooted lines are not homologues to sticky web elements of orb-weavers and present new synapomorphic characters that support the monophyly of Theridiidae + Nesticidae and the monophyly of araneoid sheet web weavers. Further, the time allocation pattern for different behavioral stages and the fine structure of a gumfooted line are presented.     

Weintrauboa, a new genus of pimoid spiders from Japan and adjacent islands, with comments on the monophyly and diagnosis of the family Pimoidae and the genus Pimoa (Araneoidea, Araneae)

The spider genus Weintrauboa new genus (Araneae, Pimoidae) is described to place two species of pimoids from Japan and adjacent islands that were formerly classified in the linyphiid genus Labulla . Weintrauboa contortipes (Karsch) new comb., the type species, and W. chikunii (Oi) new comb. are redescribed. Parsimony analysis of morphological characters provides robust support for the monophyly of the genus Weintrauboa and corroborates the monophyly of Pimoa , Pimoidae, and the clade Linyphiidae plus Pimoidae. New diagnoses for Pimoa and Pimoidae are provided.  © 2003 The Linnean Society of London, Zoological Journal of the Linnean Society , 2003, 139 , 261–281     

The effects of capture spiral composition and orb-web orientation on prey interception

Cribellar prey capture threads found in primitive, horizontal orb-webs reflect more light, including ultraviolet wavelengths, than viscous threads found in more derived, vertical orb-webs. Low web visibility and vertical orientation are each thought to increase prey interception and may represent key innovations that contributed to the greater diversity of modern, araneoid orb-weaving spiders. This study compares prey interception rates of cribellate orb-webs constructed by Uloborus glomosus (Uloboridae) with viscous orb-webs constructed by Leucauge venusta (Tetragnathidae) and Micrathena gracilis (Araneidae). We placed sectors of cribellar and viscous threads side by side in frames that were oriented either horizontally or vertically. The webs of both U. glomosus and L. venusta intercepted more prey when vertically oriented. In each orientation L. venusta webs intercepted more insects than did U. glomosus. Although this is consistent with the greater visibility of cribellar threads, the more closely spaced capture spirals of L. venusta may have contributed to this difference. Micrathena gracilis webs intercepted more prey than did U. glomosus webs, although web orientation did not affect the performance of this araneoid species. The stickier and more closely spaced capture spirals of M. gracilis may have enhanced the interception rates of this species and accounted for the greater number of smaller dipterans retained in its webs. The tendency for these slow, weak flight insects to be blown into both horizontal and vertical webs may account for similar interception rates of horizontal and vertical M. gracilis webs. These observations support the enhanced prey interception of vertically oriented orb-webs, but offer only qualified support for the contributions of lower visibility viscous capture threads.     

Dynamics of aquatic insect flux affects distribution of riparian web-building spiders

The flux of emerging aquatic insects from streams can provide a significant energy subsidy to riparian web-building spiders. However, despite the high temporality of aquatic insect emergence, the effects of such aquatic insect dynamics on spider distribution are poorly understood. To examine the relationship, the aquatic insect flux from a headwater stream in a northern Japanese deciduous forest was experimentally manipulated by using a greenhouse-type covering, during May to July. Under natural conditions, the aquatic and terrestrial insect abundances dramatically decreased and increased from May through July, respectively. The experimental reduction of aquatic insect flux depressed the density of horizontal orb weavers (Tetragnathidae) in both May and June, but not in July when aquatic insects were scarce, indicating a temporal limitation on spider distribution by aquatic insect flux. In contrast, the densities of both vertical orb weavers (Araneidae) and sheet weavers (Linyphiidae) were unaffected by the manipulation throughout the study period. These various responses, differing among months or spider guilds, may be attributed to the degree of specialization for aquatic prey in the spiders and their mobility in response to aquatic insect flux. The experimental results provided direct evidence that the temporal dynamics of aquatic insect flux, as well as spider characteristics, were primary factors determining the distributional patterns of riparian web-building spiders.