Spiders Try to Ensure Paternity

Ventral view of an Oedothorax retusus female. Red square indicates the position of the genital region (epigyne) that is plugged by the male.MELANIE WITTHUHNThe plugs that male dwarf spiders (Oedothorax retusus) insert into the copulatory ducts of females with whom they’ve just mated act to block fertilizations by other males, according to researchers studying the arthropods. “The mating plug in the dwarf spider clearly functions as a mechanical obstacle to rival males,” lead author Katrin Kunz of the Zoological Institute and Museum in Greifswald, Germany, said in a statement. “Mating plugs are a powerful mechanical safeguard whose efficacy varies with plug size and age.”

Kunz and her coauthors, who’s study of the spider’s mating habits was published yesterday (June 10) in Behavioral Ecology and Sociobiology, determined that the mating plugs are composed of a liquid material that hardens with time to block access to...