Stegodyphus lineatus

Stegodyphus lineatus is the only European species belonging to the spider genus Stegodyphus.

The males of this species are up to 12 millimeters long, while the females are up to 15 millimeters long. The coloration can range from whitish to almost black. In the majority of individuals, the opisthosoma is whitish with two broad black longitudinal stripes. The males and females look similar, but the male is usually richer in contrast and has a bulbous forehead. The species name is in reference to the black lines on the back of these spiders.

They construct a web between twigs, mostly of low thorny shrubs. The web has a diameter of about 30 centimeters and is attached to a retreat consisting of silk and covered with debris and food remains. The retreat is a cone-shaped structure roughly 5 centimeters long, which has an entrance at one end. The spiderlings hatch in this retreat, being released from their cocoon and then protected by the mother for an additional two weeks. The adult males can be found during the spring.

Offspring are matriphagous, meaning they eat their own mother. The females can mate with several males. While the females may gain some benefits from multiple matings, overall polyandry is costly and mated females are frequently aggressive towards the males. The males may change upon only one or two mates for the duration of their lifetime. Egg sacs are lost quite often because of predation by ants. The female is unable to lay another clutch if they lose their first one. This represents an opportunity for the males, however, who can secure themselves a mate by simply disposing of her offspring. The males perform this action by detaching the egg sac with their chelicerae, moving it to the entrance, then simply tossing it to the ground.

However, this behavior, known as infanticide, is not so straightforward for the females. Fitness is greatly reduced by the loss of their young, with the female being less likely to survive until her next lot of young can hatch, as well as having fewer eggs the second time. Their offspring also hatch later in the season and are less likely to prosper. With this in mind, it comes with little surprise that the females aggressively attend to their nest, chasing off around half of the males that come nearby. The males can sustain injuries in these encounters with the larger females, and in some cases, the female not only kills, but eats the male trespasser. For the males, however, there is little option but to take this risk, resulting in sexual conflict that see around 8 percent of egg sacs ruined.

Image Caption: Stegodyphus lineatus – Taken in La Azohia.Cartagena.Spain 2007-04. Credit: JoaquinPortela/Wikipedia (CC BY-SA 3.0)