I think my 3 chickens may have northern fowl mite - they have grey/black dust all around their preen glands, but only there. Is this a sign of nfm or am I being paranoid and it could just be from dustbathing where the dust sticks here because it is oily? Anyway I treated one of them previously (discussed in a post earlier this year) with both Frontline and Ivermectin but it seems to be back with a vengeance. Sadly the other 2 chickens I had were killed by a fox so my new cockerel and girls are only just 20 weeks old. I would rather give them a squirt of Frontline than 3 doses of Ivermectin but am reticent about using Frontline on the preen gland in case they ingest it. Does anyone have any feedback. I know they are both horrible drugs but powders just don't work. Boris (my new frizzle cockerel who bears a striking resemblance to Boris Johnson) has also developed a limp but I don't think the nfm would cause that?