i think it's usually agreed that aside of bugs, Yukkuris can't eat anything else, either they escape quite easily, or they end up killing the yukkuris.
And even with bugs, they tend to be repelled easily by bugs with some poison or gas like countermeasure, making their status of "higher than bugs" debatable.
So for the time being, the only thing Yukkuris are over in the chain food is flora/fungus and bugs but this sometimes outclassing the yukkuris, like when ants overwhelm them or again the ones with poison or gas, counter attacking them.