The invention relates to compounds of the general formula (I), in which Ar, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, R.sub.8, W, a, b and n are as defined in claim 1, and to any enantiomers thereof. The active ingredients have advantageous pesticidal properties. They are particularly suitable for controlling parasites in warm-blooded animals ##STR00001##