The scent gland secretion of an undetermined species of Prionostemma from Costa Rica was analyzed by gas chromatography–mass spectrometry and shown to consist of medium-chain carboxylic acids (mainly octanoic acid) and a ß-hydroxy-carboxylic acid, eventually identified as myrmicacin (= (R)-3-hydroxydecanoic acid). While scent gland secretions in harvestmen have traditionally been considered to be products of de novo synthesis, we here provide evidence for the unusual case of sequestration-derived scent gland constituents: at least myrmicacin appears to be sequestered from leaf-cutter ants that constitute a part of the prey of the Prionostemma-species herein investigated. This is the first report on the scent gland chemistry of the sclerosomatid subfamily Gagrellinae as well as on a possible sequestration mechanism in harvestmen.