I have several bantam breeds and I have noticed that they are all quite poor foragers. They include a serama, a pekin bantam, a silkie, a Belgian danver, a polish and a booted bantam.
I provide layer pellets and they free range for twelve hours a day in my large lawn garden which has just a few shrubby plants and a small tree. I live in the UK and the bugs here seem to be less exotic than in other countries, mostly small worms and slugs. The bantams will not touch the slugs though and rarely bother with worms unless they are the tiny white curled type.
I have one rooster and he leads the girls around all day but they spend very little time digging and mostly just peck at dirt and eat a bit of grass. Of the bantams I would say the serama, the smallest of all, is the most active forager and the Belgian is the least active.
I also have one large hen, an asil, and she is drastically more active at foraging. She will spend most of the twelve hours digging and scratching in the mud and high grasses and will eat virtually anything including whole snails in their shell.