I've dealt with tapeworms many times, they are difficult to get rid of. Purchase Zimectrin Gold equine paste wormer. The praziquantel in z-gold will kill tapes, it's the same as drontal/droncit. Give your birds a "pea" size amount orally to each chicken. They will wipe their beaks on the ground afterwards which is normal. Repeat dosing in 10 days.
There are only 4 wormers I know of that will kill tapeworms in chickens: Valbazen at double doses, zimectrin gold, equimax, and quest plus. The last 3 are equine wormers. I dont recommend quest plus because it requires exact measurement for dosing, there is little room for error. The zimectrin gold is the safest equine wormer of the three. I've used it without any problems.
If you wish to use valbazen, let me know...it has to be administered differently to be effective rather than redosing just one more time in 10 days.
http://www.jefferspet.com/zimecterin-gold/camid/EQU/cp/M0-Z2/
FYI: Insects are the intermediate host carrying infective tapeworm eggs. Chickens eat infected insects, chicken gets infected.