Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
vespa, ae, f. [Gr. σφήξ; O. H. Germ. wefsa; Engl. wasp], a wasp, Varr. R. R. 3, 16, 19; Plin. 11, 21, 24, § 71; 20, 13, 51, § 133; Phaedr. 3, 13, 3.