The egg sac of Benoitia lepida (Araneae: Agelenidae): structure, placement and the function of its layers

Abstract

We describe the remarkable egg sac of Benoitia lepida (O.P.-Cambridge, 1876) (Agelenidae) from the Negev Desert, Israel. It consists of four layers: (from outside) a papery envelope, an outer loose silk layer, a “dirt layer”, and an inner flocculent silk layer surrounding the eggs. The dirt layer consists of loess soil, and may include stones, snail shells, or twigs from the surroundings. Some sacs hang from a silken string over the female's web sheet, attached to barrier threads or overhanging vegetation. In these “hanging sacs”, the outer papery wall is shiny white and covers the inner layers completely. Other sacs (“attached sacs”) are attached to a top branch of a shrub, away from the female's web. These sacs often have little or no outer papery envelope; the outer silk wrapping encloses the branch, and the sac may be dull brown in color. We studied the species at two sites; at one the hanging sac type predominated, while at the other the attached type was most common. A field experiment revealed that the dirt layer is effective in protecting the sacs against predation from ants but had no effect on spider predators of the egg sacs.