We add food grade DE to the chicken feed, but I have recently thought about using a wormer on top of that. My flock is about 6 months old, and I have never used a wormer, but I want to make sure they are as healthy as possible.
One of my dogs got tapeworm and we got some WormGuard Plus SC for dogs from The Holistic Horse website. Used it as prescribed and her recent tests from the vet are clean after 90 days of use.
She had them to the point where they were crawling out of her behind (sorry for TMI), and now they are gone.