Novel 4-chloro-4,4-difluorothiobutyric acid derivatives of the formula I ##STR1## in which R.sub.1 and R.sub.2 are, independently of one another, hydrogen, C.sub.1 -C.sub.4 alkyl or C.sub.1 -C.sub.4 halogenoalkyl and R.sub.3 is hydrogen or an organic radical can be employed as pest-control agents. Control of insects and arachnids is possible and preferable.