Three things to kill them:
Garlic, tons of it at all times of the day fresh, pill form any type! I add honey and break open the capsules for the wee ones.
Neem powder, I made my own capsules, you can use this for lice as well, I have some neem oil and shampoo in case we ever get lice again.
Grapefruit seed extract, taken with orange juice is the best way to not taste it, its pretty bitter 15-20 drops 3-4x a day.
there are other things that help but these are all safe and effective.
Clove powder fresh, black walnut supplement.
There are other things but I am too tired to research them more and write.