Somebody please correct me if i am wrong, but i think Biospot is an attempt tp mimic TopSpot, otherwise known as Frontline, a very effective Flea preventitive. Unfortunately, BioSpot is a pyrethrin based drug. Pyrethrins had their time once as insecticides, but they have been around so long that many bugs are now resistant to them. Many times they will "stun" the fleas but then they eventually come out of it and go right back to biting the dog. it is alot cheaper but not nearly as effective. The old saying holds true in this case- "you get what you pay for".