Abstract Mature larva of Gonioctena (Spartoxena) variabilis (Olivier, 1790) is described and illustrated for the first time, based on specimens collected on Genista scorpius (L.) DC. [Fabaceae] in central Spain. A key to known larvae of the subgenus Spartoxena is provided, and the diagnostic characters are illustrated. Diagnostic characters for the identification of species within the subgenus Spartoxena Motschulsky, 1860 are number of dorsal tubercles of abdominal segments, shape of tarsal claw, shape of labrum and disposition of microtrichia of epipharynx. Notes on the distribution and host plant of G. variabilis are included.