The 8 month effectiveness of the Seresto collar is pretty darn accurate. This is the 8th month that I have had it on Wolfy, and I noticed him fiercely scratching starting several days ago. Last night I found a flea on him. I was hoping he could get thru the colder months without flea protection, but that's not going to happen. I sent for another collar, and in the meantime while I wait for it to get here, I found that I had one dose of Advantix II left, so I put that on him last night. No scratching today, so far. Now I have to strip the bed and also spray areas that he likes to occupy too.