Wind effects on web structure of grass spiders Agelenopsis actuosa

Abstract Habitat selection can be influenced by abiotic factors such as rain and wind. Spiders build webs that are subjected to wind, thus making habitat selection that much more important for individual spiders. I examined the webs of the grass spider Agelenopsis actuosa (Gertsch & Ivie, 1936), to determine whether they differed in shape, size, and attachment points in short versus tall vegetation in the same general area. I hypothesized that short-grass webs would be larger in diameter, closer to the ground, have more numerous attachments to vegetation, and have specific orientations that accounted for the dominant wind directions. Webs in short grass were significantly shorter in diameter (mean short = 23 ± 6 cm, mean tall = 25 ± 6 cm), lower to the ground (mean short = 7 + 3 cm, mean tall = 17 + 5 cm), and had more numerous attachments (mean short = 24 + 6 attachments, mean tall = 10 + 2 attachments) than webs in tall grass. Short-grass webs were significantly oriented towards north while tall-grass webs showed no significant web orientation. My findings suggest that short-grass webs were smaller because of the wind, and are a predictable circular shape with more attachments. Tall-grass webs were a longer oval in shape, with fewer attachments. Webs are possibly more rigid in short grass with significant orientation perpendicular to the dominant wind direction, possibly for spider thermoregulation.