Abstracts of arachnological publications by Samuel Zschokke
(on construction, structure and evolution of spider webs)

The web placement and web structure of the nine most common species of orb-web spiders (Araneae: Araneidae, Tetragnathidae) coexisting in the park-like campus of the University of Ghana in Legon, Ghana were investigated to analyse differences between their ecological niches. Various web parameters such as its relation to the habitat, height, light exposure, web size, mesh size, and web inclination were measured. When comparing these parameters in all species pairs, the webs of each species were found to differ in at least two parameters from the web of every other species. Since the analysed web parameters are all likely to influence the number and kind of prey caught, this suggests a niche differentiation between all analysed species. Some observations were also made on the prey caught. While the prey analysis was not detailed enough to find differences between all species, there was a positive correlation between the web’s mesh size and the size of the prey.

Keywords: ecological separation - microhabitat - spiral spacing - web architecture - web characteristics

"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.

Keywords: behavioral ontogeny - orb web evolution - construction behavior - costs of cribellum silk

Gravity is very important for many organisms, including web-building spiders. Probably the best approach to study the relevance of gravity on organisms is to bring them to the International Space Station. Here, we describe the results of such an experiment where two juvenile Trichonephila clavipes (L.) (Araneae, Nephilidae) spiders were observed over a 2-month period in zero gravity and two control spiders under otherwise identical conditions on Earth. During that time, the spiders and their webs were photographed every 5 minutes.
Under natural conditions, Trichonephila spiders build asymmetric webs with the hub near the upper edge of the web, and they always orient themselves downwards when sitting on the hub whilst waiting for prey. As these asymmetries are considered to be linked to gravity, we expected the spiders experiencing no gravity to build symmetric webs and to show a random orientation when sitting on the hub.
We found that most, but not all, webs built in zero gravity were indeed quite symmetric. Closer analysis revealed that webs built when the lights were on were more asymmetric (with the hub near the lights) than webs built when the lights were off. In addition, spiders showed a random orientation when the lights were off but faced away from the lights when they were on.
We conclude that in the absence of gravity, the direction of light can serve as an orientation guide for spiders during web building and when waiting for prey on the hub.

Keywords: extended phenotype - golden silk orb-weaver - microgravity - Nephila - secondary cue - sensory compensation - spider web

In almost all vertical orb webs the hub is above the geometric centre and consequently, the extent of the capture area is larger below the hub than above. In addition to this vertical web-extent asymmetry, orb webs show vertical asymmetries in number of spiral loops, mesh widths, and angles between radii. However, it was unknown whether these asymmetries are adaptations to the web-extent asymmetry or whether they are linked to gravity in a different way than through web-extent asymmetry.
We reviewed known vertical asymmetries of orb webs, and we analysed the asymmetries of webs built by four different Cyclosa species, which show large intra- and interspecific variation in web-extent asymmetry. We found all analysed structural asymmetries to be linked both to web-extent asymmetry and to gravity: Larger web extents below the hub and gravity both led to more sticky-spiral loops and to smaller angles between radii below the hub, whereas web-extent asymmetry and gravity had opposing effects on mesh width (mean and peripheral). Independent of web-extent asymmetry, almost all analyzed webs had narrower peripheral meshes and smaller angles between radii below the hub than above. We interpret the narrow peripheral meshes along the web's lower edge as an adaptation to prevent tumbling prey from escaping, and the small angles between radii as an adaptation to prevent the sticky spiral lines in these narrow meshes to come into contact with each other.

Keywords: Araneidae - Cyclosa - gravity - prey tumbling hypothesis - spider web - sticky-spiral spacing - trap - web architecture - web geometry

Most orb webs are vertically asymmetric with larger lower than upper parts, even though the basic structure of orb webs with concentric sticky spiral loops implies a round shape with the hub in its geometric centre. Spiders are known to modify the basic, round web structure to achieve asymmetric webs by placing the sticky spiral loops eccentrically around the hub and by inserting additional sticky spiral threads below the hub. In addition, spiders could increase asymmetry by building larger meshes below than above the hub. In the present paper, I analyzed these web modifications quantitatively in webs of Araneus diadematus Clerck 1757. In addition, I assessed the influence of gravity on the different web modifications during web building by laying some webs horizontally during auxiliary and/or sticky spiral building, and I also assessed how the web modifications influenced each other during web building. I found that web orientation during auxiliary spiral building influenced auxiliary spiral eccentricity, which in turn influenced sticky spiral eccentricity and overall web asymmetry. Web orientation during sticky spiral building only influenced – together with web asymmetry and spiral ratio &ndash mesh size asymmetry. I conclude that A. diadematus uses the auxiliary spiral as a guiding line during sticky spiral building and that it employs different rules to build the two spirals.

Keywords: gravity - hub displacement - up-down asymmetry - web building

Orb-web building spiders (Araneae: Araneoidea, Uloboridae) can be considered as territorial central place foragers. In territorial central place foragers, the optimal foraging arena is circular, with the forager sitting in its centre. In orb webs, the spider's orientation (head up or head down) whilst waiting for prey on the hub of its web and the downwards-upwards asymmetry of its running speeds are the probable causes for the observed deviation of the hub from the web's centre. Here, we present an analytical model and a more refined simulation model to analyse the relationships amongst the spider's running speeds, its orientation whilst waiting for prey and the vertical asymmetry of orb webs. The results of our models suggest that (a) waiting for prey head down is generally favourable because it allows the spider to reach the prey in its web on average quicker than spiders waiting head up, (b) the downwards-upwards running speed asymmetry, together with the head-down orientation of most spiders, are likely causes for the observed vertical asymmetry of orb webs, (c) waiting head up can be advantageous for spiders whose downwards-upwards running speed asymmetry is small and who experience high prey tumbling rates and (d) spiders waiting head up should place their hub lower than similar spiders waiting head down.

Keywords: biomechanics - central place foraging - spider web - gravity - up-down asymmetry - web design

Keywords: plagiarism - forged illustrations

Almost all spiders building vertical orb webs face downwards when sitting on the hubs of their webs, and their webs exhibit an up-down size asymmetry, with the lower part of the capture area being larger than the upper. However, spiders of the genus Cyclosa, which all build vertical orb webs, exhibit inter- and intraspecific variation in orientation. In particular, Cyclosa ginnaga and C. argenteoalba always face upwards, C. octotuberculata always face downwards, whereas some C. confusa face upwards and others face downwards or even sideways. These spiders provide a unique opportunity to examine why most spiders face downwards and have asymmetrical webs. We found that upward-facing spiders had upside-down webs with larger upper parts, downward-facing spiders had normal webs with larger lower parts and sideways-facing spiders had more symmetrical webs. Downward-facing C. confusa spiders were larger than upward- and sideways-facing individuals. We also found that during prey attacks, downward-facing spiders ran significantly faster downwards than upwards, which was not the case in upward-facing spiders. These results suggest that the spider's orientation at the hub and web asymmetry enhance its foraging efficiency by minimizing the time to reach prey trapped in the web.

Keywords: foraging efficiency - biomechanics - orientation - web asymmetry - gravity - hub displacement

Orb-web spiders build vertically asymmetric webs, in which the lower part is larger than the upper part. One hypothesis explaining this asymmetry suggests that the spider's mass imposes higher building costs in the upper part of the web, causing the spider to reduce this part of the web. We tested this hypothesis by assessing building costs of different parts of the web. We found that the specific time-cost of building (i.e. the time required to build a certain length of silk) differed between the two parts of the web and that the difference in time-costs influenced web asymmetry. Contrary to predictions, however, building costs were larger in the lower part of the web, suggesting that additional factors affect the spider's decisions while building the web, which are likely to be prey-capture considerations.

Keywords: Araneus diadematus - up-down asymmetry - gravity - optimal foraging - spider web

The orb-web spider Cyclosa oculata (Walckenaer, 1802) was found at eleven localities in north-western Switzerland. All records were from wildflower strips ("Buntbrachen") with a relatively high proportion of dried vegetation from the previous year, a relatively low vegetation height and a low proportion of grasses in the vegetation. C. oculata built its vertical orb-web near the ground, deep in the vegetation. Among ecribellate orb-web spiders in Central Europe, C. oculata is unique because it sometimes builds rudimentary webs on which it stays, because it builds its cocoons into the web, and because its stabilimentum is long-lasting and largely of debris. Based on our observations, we deduce that the stabilimentum of C. oculata serves as camouflage.

Keywords: faunistics - first record - habitat - rudimentary web - stabilimentum

Partial translation of publication into English

Arthropods in several orders use traps to capture prey. Such trap-building predators expend most of their foraging energy prior to any prey contact. Nevertheless, relative investments in trap construction and actual prey capture may vary among trap builders, and they are likely to face a trade-off between building very effective but energetically costly traps and building less effective traps requiring faster reaction times when attacking prey. We analysed this trade-off in a field experiment by comparing the prey capture behaviour of four different sympatric web-building spiders (Araneae: Araneidae, Nephilidae, Tetragnathidae, Theridiidae) with the retention times of five different prey types in the webs of these spiders. Retention times differed greatly among webs and among prey types. The vertical orb webs retained prey longer than the horizontal orb web and the sheet web, and active prey escaped more quickly than less active prey. Among spiders with orb webs, the spider with the web that retained prey for the shortest time was the fastest to capture prey, thus confirming the expected trade-off between building long-retaining webs and attacking slowly versus building short-retaining webs and attacking more rapidly. The sheet web, however, neither retained prey for an appreciable period of time nor facilitated rapid prey capture. We suggest that this low capture effectiveness of sheet webs is compensated by their lower maintenance costs.

Keywords: extended phenotype - foraging strategy - spider web - trap building - tumbling - web orientation

Web-building spiders are an important model system to address questions in a variety of biological fields. They are attractive because of their intriguing biology and because they can be fairly easily collected and maintained in the laboratory. However, the only published instructions for working with web-building spiders are somewhat outdated and not easily accessible. This paper aims to provide an up-to-date guide on how to best collect, keep and study web-building spiders. In particular, it describes how to obtain spiders by capturing them or by raising them from cocoons, how to keep and feed spiders in the laboratory and how to encourage them to build webs. Finally it describes how to document and analyze web building and web structure.

Keywords: data collection - laboratory manual - methodology - spider silk - spider web

Amber is well known to conserve small insects and spiders, preserving finest details of their morphology. However, spider webs in amber have so far largely been ignored, even though some webs in amber are superbly preserved; with even smallest details being visible, like the glue droplets, which retain the prey in orb-webs and other araneoid webs. Here I present a brief introduction to the occurrence and function of glue droplets in recent spider webs, followed by evidence of fossil glue droplets in Lebanese, Burmese, Baltic and Dominican ambers. A comparison of their states of preservation suggests that glue droplets in Lebanese amber have swollen up more than those in the other amber types. Finally, I discuss evidence that these droplets are indeed fossilised glue droplets.

Keywords: Araneoidea - amber - glue droplet - spider silk - taphonomy - trace fossil - viscid silk

Linyphiidae is the second largest family of spiders. Using Linyphia hortensis and L. triangularis, we describe linyphiid sheet-web construction behaviour. Orb-web construction behaviour is reviewed and compared to that of non orb-weaving orbicularians. Phylogenetic comparisons and the biogenetic law are applied to deduce behavioural homology. Linyphia webs were constructed gradually and in segments over a period of many days and had a long life span. Two construction behaviours, supporting structure and sticky thread (within the sheet) were observed. Sticky thread construction behaviour in linyphiids is considered homologous to sticky spiral construction in orb-weavers. Overall web construction conformed to the pattern of alternate construction of sticky and non-sticky parts as observed in theridiids. Linyphiids had no problem in switching between structure construction and sticky thread construction even during a single behavioural bout. Both web construction behaviours in linyphiids were non-stereotypic, which is unusual in orbicularians. This might be due to the loss of control mechanisms at genetic level, probably by macro mutation. Lack of stereotypic behaviour might have played a substantial role in the origin of the diverse web forms seen in non orb-weaving orbicularians. This hypothesis is consistent with patterns observed in the orbicularian phylogeny.

Keywords: behavioural character - evolution - Linyphiidae - macro mutation - Orbiculariae - orb-web - sheet-web - stereotypic behaviour - web construction

Understanding the web construction behaviour of theridiid (comb-footed) spiders is fundamental to formulating specific evolutionary hypotheses and predictions regarding the reduction of orb-webs. We describe for the first time in detail, web construction behaviour of Achaearanea tepidariorum, Latrodectus geometricus, Theridion sisyphium and T. varians as well as webs of a range of other theridiids. In our survey of theridiid webs, we distinguish four major web types. Among webs with gumfooted lines, we distinguish between webs with a central retreat (Achaearanea type) and those with a peripheral retreat (Latrodectus type). Among webs without gumfooted lines, we distinguish between those with a sheet, not containing any viscid silk (Coleosoma type) and those which contain viscid silk (Theridion type). Theridiid gumfoot-webs consist of frame lines that anchor them to surroundings and support threads, which possess viscid silk. Building of gumfooted lines constitutes a unique stereotyped behaviour and is most probably homologous for Nesticidae and Theridiidae. Webs remained in place for extended periods and were expanded and repaired, but no regular pattern of replacement was observed. We suggest that the cost of producing and maintaining viscid silk might have lead to web reduction, at least in theridiids.

Keywords: behavioural patterns - character evolution - capture thread - resource allocation - viscid silk - web construction - web reduction

The use of viscid silk in aerial webs as a means to capture prey was a key innovation of araneoid spiders and has contributed largely to their ecological success. Here I describe a single silk thread from a spiders web that bears glue droplets and has been preserved in Lebanese amber from the Early Cretaceous period for about 130 million years. This specimen not only demonstrates the antiquity of viscid silk and of the spider superfamily Araneoidea, but is also some 90 million years older than the oldest viscid spider thread previously reported in Baltic amber from the Eocene epoch.

Keywords: amber - glue droplet - spider silk - trace fossil - viscid silk

News stories relating to this article:
National Geographic News: Dinosaur-Era Spiderweb Found in Amber
BBC: Oldest spider silk found

To determine the reflectance of spider webs and spiders under ultraviolet (UV) light, spiders and their webs were photographed under normal (white) light and under UV light. It was found that all silks in araneoid webs reflect slightly more UV light than white light; i.e., they had a positive UV-brightness. However, the often cited, particularly high UV-brightness of stabilimenta could not be confirmed. Spiders differed in their UV-brightness, with most spiders reflecting less UV light than white light. Based on the knowledge of the visual system of insects and invertebrates it is suggested that the main function of stabilimenta is predator defense. However, drawing a final conclusion requires more knowledge on the way potential predators and prey perceive spiders, spider webs and stabilimenta.

Keywords: stabilimentum - camouflage - predator-prey - spider silk - visibility

Fig. 14 in color

Spider webs are a record of the application of a series of behavioural patterns. Web building behaviour is of great interest to ethologists and taxonomists studying the evolutionary relationships of spiders. However, due to the inability of the researcher to observe the spider around the clock during web building, many details of the behavioural patterns remain undetected. To overcome this problem we developed a novel, computerised method to continually observe the spider during web building. The spider is kept in a temperature-controlled room, on a reversed light cycle, confined to an observation arena placed in front of an infrared illuminated background. An infrared sensitive digital video camera is used to capture live images, which are transferred to a computer where they are analysed in real time. A separate program allows a detailed study of the recorded movements, including various spatial and temporal analyses. It also allows for the export of movement patterns. The method of observation and data analysis developed by us, enables the detailed study of the web building behaviour of nocturnal spiders and eliminates most constraints encountered to date. Due to the inaccuracy of human observation of long chains of behavioural events and the stereotypic nature of web building behaviour, computerised observation systems are preferable.

Keywords: Araneae - spider - web building behaviour - computerised observation - computerised data analysis

We examined the webs of Linyphia triangularis (Clerck) and Microlinyphia pusilla (Sundevall) using light and scanning electronic microscopic techniques and compared them with the better known orb-webs. The linyphiid sheet-web consists of an unordered meshwork of fibres of different thicknesses. The sheet is connected to the scaffolding by the means of attachment discs. Thin threads with globules, which appear similar to the viscid silk droplets of orb-webs are present in most webs examined. Webs of M. pusilla had a higher density of these globules than did webs of L. triangularis. Webs of both species possess five types of thread connections and contain no aqueous glue for prey capture. Instead, unlike orb-webs, the sticky substances produced by the linyphiid aggregate glands cement the different layers and threads of the sheet by drying up after being produced. Due to the function, sheet webs may not require viscid silk, thereby leading to a more economic web. The assumption made in most previous studies, that the globules in linyphiid webs have the same properties and function as viscid silk in orb-webs, is unfounded.

Keywords: sheet-web - thread connection - sticky silk - silk properties - silk use - prey capture

In the present article, I review physical and biological constraints spiders face when they construct and use orb-webs and I show how these constraints influence the form of the orb-web. Using the orb-web of the common garden cross spider Araneus diadematus as an example, I illustrate and explain a number of features of the orb-web and show alternatives employed by other spider species in their webs. In particular, I discuss why the orb-web generally is planar and vertical, why it has a radial structure with concentric loops of sticky silk, producing a regular meshwork, and why it has a top-down asymmetry. Furthermore, I discuss possible reasons for the increasing distance between the sticky silk loops from the centre to the periphery of the web and the function of the secondary frame threads. I conclude that the shape of the orb-web is a logical consequence of various constraints and optimisations and can therefore not be taken as evidence for a monophyletic origin of the orb-web.

Keywords: animal architecture - biomechanics - evolution - orb-web - web construction - web design

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.

Keywords: web construction - behavioral pattern - capture thread - viscid silk - phylogeny - Steatoda - Theridiidae - theridioids

Orb-weaving spiders build more or less planar webs in a complex, three dimensional environment. How do they achieve this? Do they explore all twigs and branches in their surroundings and store the information in some form of mental map? Or do they at first just build a cheap (i.e. few loops, possibly non-planar) web to test the site and - if this first web is successful (i.e. the web site is good) - later build subsequent improved and enlarged webs, by re-using some of the anchor points and moving other anchor points? The second hypothesis is supported by the fact that the garden cross spider Araneus diadematus Clerck (Araneidae) usually builds several webs at the same site, re-using structural parts of one web for subsequent webs. To further test the second hypothesis, we measured and assessed the planarity of first and of subsequent webs built in the field and in the laboratory.
First webs built at a new site in the field or in the laboratory were less planar and less vertical than subsequent webs. Furthermore, first webs built in the laboratory also had fewer loops in their sticky spiral. Our observations thus support the hypothesis that these orb-weaving spiders follow a risk-minimising strategy of first building a low-investment pilot web which on renewal may be improved and enlarged.

Keywords: Araneidae - orb-web - behaviour - optimal foraging - decision making - web construction

In orb-webs, the tension of the sticky spiral produces a centripetal force on the radii, resulting in an increase in tension along each radius from the centre of the web to the periphery. Zilla diodia (Walckenaer, 1802) atypical of araneids, was found to adapt the structure of its radii to this tension gradient by building radii that are double stranded at the periphery of the web and single stranded near the centre. Furthermore, the proportion of each radius that is doubled was found to be larger in the upper part of the web - where the overall tensions in the radii are known to be higher - than in the lower part of the web, suggesting that the spider adjusts the proportion of each radius that is doubled to the overall tension in the radius.

Keywords: adaptation - animal architecture - biomechanics - spider web - tension control - web construction

H. paradoxus - well known for its characteristic triangular web - has frequently been described to always completely collapse its web when catching prey. The aim of the present article is to show that this is not the case, and to discuss how the myth of the obligate complete collapse of the web has arisen and why it survived so well.

Keywords: Hyptiotes sp. - triangle spider - prey capture - meme

In the literature on orb-webs and orb-web construction, different terms are used for the same part of the web and - even worse - the same term is used by different authors for different parts of the web. This paper tries to improve the situation by proposing a nomenclature for the different parts of the orb-web. At the same time, it gives an overview of the terms in English, German and French used by various other authors.

Keywords: auxiliary spiral - hub - radius - sticky spiral - U-turn

The size of the web built by Araneus diadematus is influenced by several factors. The single most important factor is - of course - the size of the spider, but other factors also play a role. One of these factors is the supply of silk in the glands of the spider. In this study, the influence of the supply of silk (deduced from the time since the spider had built its previous web) on the size of the web is quantitatively analysed. It was found that the time since the spider had built the previous web significantly influenced the size of the current web, but only if the current web was built within 20 hours after the previous one.

Keywords: gland depletion - resource depletion - web size

The early stages of orb web construction are the least studied and the most poorly understood, because the behaviour of the spider at that stage lacks the repetitiveness of later stages, the timing is unpredictable and the moves of the spider cannot be deduced from the finished web.
In the present study, all moves of the spider during web construction were recorded using computerised image analysis. The early stages of web construction of several webs were then reconstructed from these recordings and analysed in detail.
The construction leading to the proto-hub was found to be highly variable. It was also found that during its construction, the spider employs a series of fixed behavioural patterns in seemingly random order. These patterns are 'designed' in a way to make it very likely that a proto-hub will emerge. Once the spider had established this proto-hub, its behaviour became more stereotyped and predictable.
The costs to explore a new site were estimated by measuring the distance walked by the spider. These costs were compared to the costs of adapting the framework of an existing web and it was found that rebuilding an existing web costs much less compared to building a web from scratch.

Keywords: spider - web - construction - behaviour - behavioural pattern - exploration - behavioural costs - animal tracking

Which way round do spiders build their orb webs, clockwise or anticlockwise? This is a question one regularly hears from interested lay persons. There is of course no simple answer, because it depends which side you observe web construction from. Preliminary studies (unpublished) using a standardised side of observation revealed no preference for building the capture spiral clockwise or anticlockwise. Here I try to answer the question: when and how is the direction of the spiral coiling in the webs of Araneus diadematus Clerck determined?

Keywords: behavioural rules - laterality - orientation

Spiders webs reflect the builders behaviour pattern, yet there are aspects of the construction behaviour that cannot be 'read' from the geometry of the finished web alone. Using computerised image analysis we developed an automatic surveillance method to track a spider's path during web-building. Thus we collected data on two orb-weaving spiders - the cribellate Uloborus walckenaerius and the ecribellate Araneus diadematus - for web geometry, movement pattern and time allocation. Representatives of these two species built webs of similar geometry but they used different movement patterns both spatially (which we describe qualitatively) and temporally (which we analyse quantitatively). Most importantly, temporal analysis showed that the two spiders differed significantly in some but not all web-building stages. From this we deduce that Uloborus - but not Araneus - was constrained by speed of silk production during the construction of its capture but not its auxiliary spiral.

We present and compare the spatial and temporal patterns of the capture web-building behaviour in different species from a range of orb weaving and non-orb weaving genera. Species analysed include: Araneus diadematus, Araniella cucurbitina, Larinioides patagiatus, Zilla diodia, Cyclosa insulana, Argiope bruennichi, Argiope lobata, Gasteracantha cancriformis, Cyrtophora citricola, Zygiella x-notata, Nephila clavipes, Uloborus walckenaerius, Zosis geniculatus, Hyptiotes paradoxus, Fecenia singaporiensis, Psechrus sp.

Keywords: spider - orb-web - web construction - tracking - activity pattern

The thesis consists of seven papers/chapters, describing various aspects of the construction of different parts of the orb web. The chapters are arranged chronologically', according to which part of the web construction they describe.
The first chapter ('Early stages of orb web construction in Araneus diadematus') features descriptive, pictorial accounts of the way Araneus diadematus starts the construction of a new web. We focused on the so-called exploration phase, describing the establishment of a proto-hub. Additionally we also assessed the costs to the spider during exploration of environments of different complexity and compared them to the costs to rebuild an existing web. It turned out, that the costs of exploring are higher in a complex environment compared to a simpler environment, but also that the rebuilding costs were always much lower than the costs to build a web from scratch.
In the second chapter ('Planarity of orb webs built by Araneus diadematus under natural and experimental conditions') we measured the position of the anchor points of orb webs in three dimensional environments in the laboratory and in the field to assess how well these points lie in a plane and whether the spider improves the position of these anchor points when rebuilding a web. We found that it seems that the spider first builds a trial web to test the site. Upon renewal, this web is enlarged and the position of its anchor points improved.
The third chapter ('Unfreezing spider behaviour: Orb web geometry and construction behaviour') describes our method to track the moves of the spider in detail, and discusses in detail our recordings of the web construction of the ecribellate spider Araneus diadematus and of the cribellate spider Uloborus walckenaerius. The main result was that the construction speed of cribellate spiders is limited by the production of the cribellate silk, whereas the rate-limiting step in the ecribellate spiders seems to be the attaching of the spirals to the radii.
In the fourth chapter ('The influence of the auxiliary spiral on the capture spiral in Araneus diadematus Clerck (Araneidae)') we describe how gravity affects the shape of the auxiliary spiral, and how shape and coiling of the auxiliary spiral, but not gravity, influence shape and coiling of the capture spiral.
The fifth chapter ('The coiling of the spirals in the orb web of Araneus diadematus') is a short description of when and how the coiling of the auxiliary spiral is determined.
In the sixth chapter ('Factors influencing the size of the orb web in Araneus diadematus') we show that the size of the web depends (all else being equal) on the time interval between two subsequent web constructions, provided this interval is less than roughly 24 hours. If this was the case, longer intervals lead to larger webs. If the interval was longer than 24 hours, no correlation between length of the interval and the size of the web could be detected.
In the last chapter ('Web construction patterns in a range of species') we expanded the horizon to the web construction of other web weaving spiders. We describe (pictorially and to some extend quantitatively) the moves recorded during web construction of spiders from 14 orb weaving and 2 non orb weaving genera.
In the appendix you can find the nomenclature for the orb web used in the thesis, together with equivalent names used by other authors.
The manuals of the computer programs we developed and used to record the moves of the spider are also included in the appendix.

The relationship between direction of coiling and shape of the auxiliary spiral and that of the capture spiral in orb webs of Araneus diadematus Clerck (Araneidae) was investigated. In most webs, the two spirals had the same direction of coiling and a similar shape, indicating that the auxiliary spiral serves as a guide during construction of the capture spiral. Additionally, it was found that the direction of gravity determined the shape of the auxiliary spiral, whereas the shape of the capture spiral was solely determined by the shape of the auxiliary spiral and was not influenced by the direction of gravity. Possible causes and mechanisms are discussed.

Keywords: behavioural rule - coiling similarity - orb-web - orientation - web shape