humm... CFB's? Well here's my thoughts: CFB's are mostly aquatic, so I'd go with water foods first(earthworms,tubifex,brine,black/bloodworms). But if you wanted terrestrial food: try waxworms, or smaller nightcrawlers, possibly cut in half. Crickets if ORDERED/BOUGHT "small" enough would be a treat(dont get the LFS's 3/4---adults, too big), but I find CFB's to be slow so I give them "slow" foods. Also, crickets will get into the water and drown too as a side thought.
If you try this, let me know how it turns out.
Cataldo.