Effect of web inclination on debris-induced damage in Leucauge venusta webs (Araneae: Tetragnathidae)

Spiders are among the most conspicuous trap builders in nature, and the structure and orientation of spider webs are presumably under strong selection pressure. Most ecribellate orb-weavers (Araneoidea) build vertically-orientated webs (0°; ie the plane of the web is orthogonal to the ground). However, Leucauge venusta (Tetragnathidae; Walckenaer, 1842) often build horizontally-orientated webs (90°; ie parallel to the ground), despite evidence that prey capture and retention rates are higher in vertical webs. Falling debris is a common hazard for webs in the forest understory, and basic geometry predicts that vertical webs sustain more damage when struck by a falling object. Here, we quantified the angle of web inclination in L. venusta and its effect on the amount of damage sustained from falling debris. We experimentally damaged L. venusta webs in the laboratory and measured natural damage to webs in the field. As predicted, webs inclined 30° or 45° relative to vertical in the laboratory sustained more damage than horizontal (90°) webs; by contrast, the proportional damage observed in the field was not related to web inclination (which ranged 21° to 90°). Thus, under controlled laboratory conditions, the horizontal orientation of L. venusta webs minimizes damage from debris fall. However, falling objects are just one of many potential sources of web damage in nature, and the relevance of web size and location to the frequency and magnitude of damage remains unclear. The results improve our understanding of the role of web orientation in the balance between prey capture and local environmental challenges.