3-(Het)aryloxy(thio)carboxylic acid derivatives of the formula I ##STR1## where R.sup.1 is hydrogen, COOH or a radical which can be hydrolyzed to give COOH;R.sup.2 and R.sup.3 are each halogen, alkyl, haloalkyl, alkoxy, haloalkoxy or alkylthio;X is nitrogen or CR.sup.14, where R.sup.14 is hydrogen or, together with R.sup.3, forms a 3-membered or 4-membered alkylene or alkenylene chain, in each of which a methylene group is replaced by oxygen;R.sup.4 is alkyl, cycloalkyl, cycloalkenyl, alkenyl or alkynyl, each of which is unsubstituted or substituted;an unsubstituted or substituted five-membered or six-membered heteroaromatic structure containing one to three nitrogen atoms or one sulfur or oxygen atom;unsubstituted or substituted phenyl or naphthyl;R.sup.4 and R.sup.5, together with the neighboring carbon atom, form a 3-membered to 8-membered ring which may contain an oxygen or sulfur atom and which is unsubstituted or substituted;R.sup.5 is hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, haloalkyl, alkoxyalkyl, alkylthioalkyl or phenyl, each of which is unsubstituted or substituted;R.sup.6 is unsubstituted or substituted phenyl or naphthyl or an unsubstituted or substituted five-membered or six-membered heteroaromatic structure containing one to three nitrogen atoms or one sulfur or oxygen atom;Y is sulfur or oxygen or a single bond; andZ is sulfur or oxygen.