stabilimentum

A stabilimentum (plural stabilimenta) is a conspicuous silk structure added to the orb webs of some spiders, most commonly members of the family Araneidae such as species of Argiope and Cyclosa. Stabilimenta appear in a variety of shapes, including zigzags, crosses, spirals, and dense discs, and are often made of white or highly reflective silk that can be visible in both human and ultraviolet wavelengths.

The function of stabilimenta has been the subject of extensive study and debate. Proposed explanations include attraction of prey (by reflecting ultraviolet light that draws insects), camouflage or disruptive coloration for the resting spider, warning signals to reduce accidental destruction of webs by large animals, reinforcement of web strength, thermoregulation, and communication with other spiders. Empirical results have been mixed: some experiments find associations with increased prey capture or reduced bird strikes, while others report no benefit or context-dependent effects.

Behavioral and ecological observations show that production of stabilimenta can vary with species, developmental stage, time of day, season, and environmental conditions. Some spiders add or remove stabilimenta adaptively in response to prey availability or disturbance. Because outcomes differ among species and experimental contexts, the stabilimentum remains an active area of research in arachnology, highlighting complex trade-offs in spider web design and signaling.