The web of Uloborus diversus (Araneae: Uloboridae)

The construction behaviour, design, and function of the orb webs of Uloboi sus are discussed in detail. The major phases and many of the details of construction behaviour are similar to the orb construction behaviour of some araneids. Frame threads are laid in a relatively fixed order, and are often made with a single set of movements repeated over and over. Radii and hub threads are laid after most of the frame threads are in place. Radii are connected to each other by the hub thread, and are actually continuous with it. A temporary spiral of non-sticky silk is laid starting at the hub and ending near the edge of the web. Tertiary radii are laid during construction of the temporary spiral and are continuous with it. Sticky spiral construction behaviour varies slightly with the site in the web but is very similar to that of Araneus diadematus. The behaviour of one leg following another in both time and space is described for the first time in spiders. Three types of web repair are described, one for the first time. The paths taken by spiders during radius construction (deduced from study of the hubs of completed webs), and the bending of radii by hub and temporary spiral threads suggest that all radii in a U. diversus web are not under equal tensions. The lack of secondary frame threads results in unequal stressing of some frame threads. Considerations of the structural properties of an orb imply these inequalities in tension probably lower web stability. The correlation between radius length and inter-radius angle, the sites of tertiary radii, and the bending of radii by the temporary spiral all indicate there has been selection to keep the distance between adjacent radii below some maximum value. Possible reasons for this are discussed. The outer loop of sticky spiral differs from those of many araneids in several respects, and probable functions of some of its characteristics are discussed. The site of the outer loop of sticky spiral is influenced by the site of the outer loop of temporary spiral. The spacing between loops of sticky spiral varies with radius length and with distance from the hub, but the functions of these variations are not clear. Changes in the average spacing between loops of sticky spirals on successive webs of individuals and in repair zones constructed the day of web construction imply that the spacing between loops of sticky spiral on a given web is probably influenced by the amount of silk available in the spider. The sticky spiral of U. diversus differs from those of all known araneids in not being attached to each radius it crosses, but the function of this characteristic is not clear. Many of the patterns in the web imply the spider adjusts its construction behaviour on the basis of cues received from its web. It appears that the spider can differentiate between sticky and non-sticky silk, and can sense the angles between radii while at the hub, the distance between radii and the distance to a frame thread during temporary spiral construction, the lengths of radii during sticky spiral construction, and probably the area to be covered by sticky silk and the amount of sticky silk available. There is evidence that adjustments are made on the basis of additional information, and possible sources of this information are discussed. Although the webs of U. diversus differ from the known webs of araneids in several respects, they do not give clear evidence that the family Uloboridae should be separated far from the family Araneidae. In general, there is more variation in web types within the Araneidae than between those of U. diversus and the araneids.