Unfortunately, as far as I know - please let me know if you know otherwise - no study has been published that gives definitive information as to the prey list of Cephalotus, so the following information is a very rough generalisation.
Cephalotus follicularis, being a ground hugging plant, attracts mainly (but not exclusively) crawling insects. Ants seem to be a particularly common victim, and in the vicinity where Cephalotus grows the species of ant found includes the Nothomyrmecia macrops, the Bulldog ant and the Argentine ant, this last one being an alien import. Other ground crawling and small flying insects are also potential victims.
Here in the UK, natural prey found in the pitchers of my plants includes: sciarid flies, fruit flies, gnats, ants and the occasional wood louse (pill bug).