@Animandel - I disagree with @Drentel. I think the chemicals in flea and tick collars may be doing more damage than we know. Besides, with all we know about chemicals and pesticides in general it makes sense to use a natural flea collar. I could understand if we only had the old chemical loaded collars, but since we have chemical-free ones we should use them.
I think natural, chemical-free collars are even more important when you have cats because they are more likely to be affected by the harsh chemicals than dogs are.