Purple Tiana worms are Taina worms that haven't ate someone's insides and are usually created when fired out of a blaster such as Upinzani's Taina worm blaster.
The Taina is a worm like Rahi that has the ability to eat the insides of it's enemies and was created by Luonto when he was a Toa. The Taina can also be created by Pateri because he took Luonto's elemental powers when he turned him into a Turaga and Wasomi can also create Taina worms because he has Pateri's dark elemental powers. Taina worms don't attack or eat the insides of those who summoned or created them.

Kanohi Taina which has the ability to create a Taina worm inside the user which then eats their insides and flies out of their chests.
Taina worm flying out of Toa Nadharia.