Naherbstural flea products refers to products that either contain citrus extract or ones that contain peppermint and lemon grass extracts. Most of the citrus extract products have a dog only label on them. These products can kill cats. Toxic reactions can also happen to animals when the peppermint/lemon grass extract products are applied.
If you decide to apply these products to your cat or dog, read the labels carefully about adverse events and antidotes, if any. NEVER put a dog flea product on a cat. Almost always toxic to a cat.