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The fact that female wasp spiders have numerous sexual contacts is something which their male partners cannot prevent. What they can do, however, is ensure that no offspring ensue from these tte ttes with their rivals: the male spiders simply place a chastity belt on their partner while copulating. The tip of their genital breaks off during intercourse, blocking the sexual orifice of the female spider. Biologists from the universities of Bonn and Hamburg report on this amazing mechanism in the journal Behavioral Ecology (vol. 18, pages 174-181, 2007).
When a male wasp spider discovers a potential partner, he attracts her by shaking her web. The female thereupon supports herself on her long legs on the web so that the male, who is much smaller, can then creep under her body. The rest works hydraulically: the tip of a transformed leg filled with sperm is inserted into the females sexual orifice like a ski boot in its binding.
The female usually puts an end to the affair after a few seconds by attacking her partner and killing him if he does not escape in time. When the male detaches himself from the female, in more than 80 per cent of cases the tip of his genital breaks off, the Bonn lecturer Dr. Gabriele Uhl says. The tip then remains in the sexual orifice like a cork, blocking it.
Together with her colleague Professor Jutta Schneider and the behavioural biologist Stefan Nessler (both now at the University of Hamburg), Dr. Uhl has been looking for a reason for this genital mutilation. There are basically two hypotheses, she explains. On the one hand detaching part of the genital organ could help the male to escape from the females murderous attack. On the other hand it might be a mechanism ensuring that paternity is maintained, preventing or impeding further copulation by the female.