We investigated the effect of exogenously administered 20-hydroxyecdysone (20E) on sexual behavior and on contact sex signals of adult females of the spider Tegenaria atrica. In untreated or control females cannibalism occurred in 36-47% of encounters, whereas no cannibalism at all was observed with 20E-treated females. The frequency of sexual receptivity was low (42%) in untreated or control females and high (100%) in 20E-treated females. Variability of female sexual behavior could be related to quantitative changes in web and cuticular compounds. We showed that 20E altered the production of polar contact sex pheromones on web and cuticle: methylesters and fatty acids are produced in higher amounts in 20E-treated females. Bioassays demonstrated clearly that methylesters and fatty acids of webs and cuticles were involved in attraction of males. Moreover, bioassays with synthetic substances showed that four fatty acids (myristic, pentadecanoic, hexadecanoic, and oleic acids) and one methylester (methyl stearate) are particularly effective in eliciting sexual behavior in males. In T. atrica, 20E inhibits cannibalism during sexual activity and changes sex pheromone production.