The dietary significance of spider web placement as determined by molecular gut-content analysis

The Linyphiidae are a numerically dominant family of small, web-building spiders whose ecology is of central importance to the function of arthropod communities in agroecosystems. However, their importance within these communities has not translated into widespread or systematic attention in the ecological literature. Even some of the most fundamental aspects of linyphiid ecology are not well understood. Recent work has suggested that these spiders can fill an augmentative role in biological control programs, but before such programs can be adopted, an understanding of the factors that impact the feeding ecology of linyphiid spiders must be investigated. One important factor is the selection of web sites, which influences the types of prey to which spiders are exposed. Here, web-placement data collected in the field are presented for three species of linyphiid spider (Tennesseellum formicum, Erigone autumnalis and Grammonota inornata) and one species of tetragnathid (Glenognatha foxi) inhabiting alfalfa fields. Height of the web and usage of attachment structures varied by species, such that each species inhabited a unique spatial niche. Such micro-habitat differentiation promotes a more diverse spider community, and can be a means of trophic specialization for sit-and-wait predators, whose diet is primarily determined by prey availability in the environment. Analysis of sticky trap catches using a pairwise design revealed a significant correlation between height off the ground and activity density of Collembola, one of the most important prey taxa for linyphiid spiders. These data indicate that diet plays an important role in micro-habitat selection by web-building spiders.