Females ofApanteles melanoscelus(Ratzeburg), a braconid parasite of the gypsy moth,Lymantria dispar(L.) (Lepidoptera: Lymantriidae), responded to silk deposited on leaves or artificially wrapped on filter paper by examining such areas intensely with their antennae. This examination behavior increased the parasite's chances of finding hosts. As few as 10 silk strands could be detected, and active silk components were not destroyed by aging or heating. Silk from other lepidopterous species was not nearly as effective as was gypsy moth silk. Water deactivated silk but organic solvents did not. Smears and water extracts of host silk glands released examination behavior especially when combined with water-deactivated silk. Conclusions are that water-soluble silk chemicals (kairomones) are important in the response of the parasite to silk, but water-insoluble chemicals and/or physical properties of the silk also influence the parasite's behavior.