They are chewing the millipedes, and then rubbing the saliva and millipede into their fur to act as an insecticide against malaria carrying mosquitoes.
However, this produces an unexpected side effect – the chemicals appear to send them into a “trancelike state” and a “condition of complete intoxication”.
https://www.discoverwildlife.com/tv/lemurs-licking-millipedes-bbc
They are chewing the millipedes, and then rubbing the saliva and millipede into their fur to act as an insecticide against malaria carrying mosquitoes.
To be fair, the anti-malarial drug Meflaquine/Larium does the same thing to people a bit after you take it.