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Virgin female spiders allow their nieces to eat them alive

Photo credit: Sylvain REMY

Velvet spiders (Stegodyphus dumicola) appear to have a dark side to their social behavior. Researchers from Ernst Moritz Arndt University in Germany and Aarhus University in Denmark discovered that female virgin velvet spiders do not only help relatives in raising their young, but also offer themselves to be eaten alive by the spiderlings.

Their published paper in the journal Animal Behavior outlines their study of the spiders and the possible advantages they get from allowing females that never mate to be eaten by young members of the colony.

The velvet spiders live in southern Africa and build large webs on shrubs and small trees and these webs can grow quite large because the spiders don’t use glue droplets to hold their webs together. The spiders work together to build and maintain their webs and nests and to raise their young.

Previous research has shown that after laying her eggs and tending them until they hatch, the spiderlings emerge and eat their mother alive by injecting chemicals into her body that dissolve her organs. Sketchy evidence has suggested that the same fate may befall close female virgin relatives.

To test this theory, the researches gathered around 200 female spiders that were ripe for laying eggs and put them in a closed environment for observation. Researchers observed that in 97 percent of cases both mated and virgin spiders who tended to the eggs and the spiderlings that emerged got eaten alive by the young ones. Researchers suggest that such a behavior has evolved due to the difficulty of finding food in the harsh and dry climate where they live.

However, one big question remains, what triggers the physical process in the adults who are willingly giving themselves up to be eaten? We know the mother has no choice in the matter, she will get eaten alive by her underlings whether she likes it, once the spiderlings emerge they inject her with chemicals to dissolve her organs in order for them to eat her but this isn’t the case with the virgin relatives. The researchers would like to know how this process starts in the virgins.

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