Observations on the Web and Behavior of Wendilgarda Spiders (Araneae: Theridiosomatidae)

Theridiosomatidae are a small family of mostly tropical spiders that are related to the common orb-weaver family Araneidae. It is known that theridiosomatids spin modified orb-webs, but only the web of the holarctic Theridiosoma gemmosum (C. L. Koch) has been studied in any detail (McCook, 1889; Wiehle, 1931). Recently we independently discovered the unusual webs of some tropical theridiosomatid spiders that the senior author later identified as belonging to the genus Wendilgarda. The architecture and operation of these webs are unique among known spider webs. The sticky lines of the web are connected to the surface films of moving streams, and moreover are under considerable tension, more tension than can be accounted for by the action of water surface tension on an inert filament alone. The attachment of the sticky lines to the water surface is integral to the operation of the web. The sticky lines function by ensnaring insects that are themselves on the surface film of the water and are floating downstream.