Fine structure of sheet-webs of Linyphia triangularis (Clerck) and Microlinyphia pusilla (Sundevall), with remarks on the presence of viscid silk

We examined the webs of Linyphia triangularis (Clerck) and Microlinyphia pusilla (Sundevall) using light and scanning electronic microscopic techniques and compared them with the better known orb-webs. The linyphiid sheet-web consists of an unordered meshwork of fibres of different thicknesses. The sheet is connected to the scaffolding by the means of attachment discs. Thin threads with globules, which appear similar to the viscid silk droplets of orb-webs are present in most webs examined. Webs of M. pusilla had a higher density of these globules than did webs of L. triangularis. Webs of both species possess five types of thread connections and contain no aqueous glue for prey capture. Instead, unlike orb-webs, the sticky substances produced by the linyphiid aggregate glands cement the different layers and threads of the sheet by drying up after being produced. Due to the function, sheet webs may not require viscid silk, thereby leading to a more economic web. The assumption made in most previous studies, that the globules in linyphiid webs have the same properties and function as viscid silk in orb-webs, is unfounded.