Permethrin is for external use only. For internal worms you will need to see your vet.P.s Is the permethrin to treat external parasites?
I don't think it's available for chickens here in the UK but I managed to get rid of the bugs pretty quickly with the treatment I used and haven't seen any signs of any more since. I will be keeping a close eye on it though.

Hens go broody when you don’t want them to… and won’t go broody when you do. 

So glad you decided to join!
Make yourself at home here.
