I know I am late in writing this all up but I have been posting this stuff for months now...
Once you take Real Vervaine on a regular basis any time a Tapeworm comes out of dormant state to feed it gets drunk on Vervaine and can't go back to dormant.
This is also what rules your dosage, obviously 5 Tapeworms are going to absorb less Real Vervaine than 500.
In the beginning most people have multiple species of Tapeworms, instead of treating each one you can just use Vervaine Frq to treat all. Of course dowsing which one to treat is better…
Later this will narrow to 2 species and finally T.Serialis is all that is left so you can start treating specifics.