EkolÛgia (Bratislava) Vol. 19, Supplement 3, 307-318, 2000 PLANARITY AND SIZE OF ORB-WEBS BUILT BY ARANEUS DIADEMATUS (ARANEAE: ARANEIDAE) UNDER NATURAL AND EXPERIMENTAL CONDITIONS SAMUEL ZSCHOKKE1,2,3, FRITZ VOLLRATH1,2,4 1 Department of Zoology, South Parks Road, Oxford OX1 3PS, United Kingdom. 2 Zoologisches Institut, Universit‰t Basel, Rheinsprung 9, CHñ4051 Basel, Switzerland. 3 Institut f¸r Natur-, Landschafts- und Umweltschutz, Universit‰t Basel, St. Johanns-Vorstadt 10, CH-4056 Basel, Switzerland. Fax: +41 61 267 08 32. E-mail:
[email protected] 4 Department of Zoology, Universitetsparken B135, DKñ8000 Aarhus C, Denmark. 3 Address for correspondence Abstract ZSCHOKKE S., VOLLRATH F.: Planarity and size of orb-webs built by Araneus diadematus (Araneae: Araneidae) under natural and experimental conditions. In GAJDOä P., PEK¡R S. (eds): Proceedings of the 18th European Colloquium of Arachnology, Star· Lesn·, 1999. EkolÛgia (Bratislava), Vol. 19, Supplement 3/2000, p. 307-318. Orb-weaving spiders build more or less planar webs in a complex, three dimensional environ- ment. 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 ñ if this first web is successful (i.e. the web site is good) ñ later build subsequent improved and enlarged webs, by re-using some of the an- chor 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.