Evolution of predator-prey systems: Spider foraging plasticity in response to the visual ecology of prey

Nephila clavipes, a large, orb-spinning spider, is distributed throughout the Tropics and Subtropics and forages in a variety of forest, nonforest, and edge habitats. In this article we show that N. clavipes spin silks of varying spectral properties in response to both the intensity and spectral composition of its light environment. In bright light characterized by broad irradiance spectra, N. clavipes produce a complex of yellow pigments that absorb light of wavelengths less than 500 nm, making their webs appear golden. In dim light and where wavelengths less than 500 nm have been eliminated, N. clavipes produce pigments that reflect light between 400 and 500 nm, making their webs appear white. Because yellow serves as a superstimulus attracting both herbivorous and pollinating insects, yellow silks may attract prey to spider webs. By training Trigona fluviventris, a stingless bee commonly fed on by N. clavipes, to forage at an artificial feeding site, we found that silk color affects insect response in two ways. First, yellow webs attract and intercept T. fluviventris more frequently than webs of any other color. Second, even after being intercepted once, T. fluviventris have difficulty learning to avoid yellow webs. We propose that N. clavipes has evolved a foraging behavior that makes use of the color cues insects seek while foraging and that the broad distribution of N, clavipes results from the spiders' ability to adjust the reflectance properties of its silks relative to its local light environment, allowing spiders to make use of whatever local populations of prey are most abundant.