Orb webs constructed by members of the spider family Uloboridae are characterized by the presence of cribellate thread on frame lines and cribellate thread placed on radii to form zig-zag patterns in a web's perimeter. Both features are added before more typical, fully circular capture spiral production begins. Zig-zags give the impression that a spider is filling in the gaps between a web's outermost spiral and frame line, although they are constructed before capture spiral turns begin. We examine these traits in orb webs of six species (Philoponella vicina (O. Pickard-Cambridge, 1899), Siratoba referens (Muma & Gertsch, 1964), Uloborus glomosus (Walckenaer, 1841), Uloborus trilineatus Keyserling, 1883, Waitkera waitakerensis (Chamberlin, 1946), and Zosis geniculata (Olivier, 1789). In four species, the distance between the outermost capture spiral and frame line was correlated with the length of cribellate thread on a radius. A web's capture area increased as the area encompassed by zig-zags was added to that encompassed by the outermost fully circular cribellate spiral thread and again when cribellate thread on frame lines was included. When constructed in frames of the same size, webs of S. referens and U. glomosus were less symmetrical and contained more capture thread switchbacks per spiral turn and per web area than did horizontal orb webs of Leucauge venusta (Walckenaer, 1841) (family Tetragnathidae). Features in the perimeter of uloborid webs may adapt these small spiders to irregular spaces within vegetation by allowing them to cover larger portions of their webs with sticky lines.