Normal
He won't be able to ingest the mulch. The mulch provides no "liquid" to the tarantula. When a tarantula bites a cricket, the inside of the cricket turns to liquid from the venom. When a tarantula bites mulch, it does nothing because mulch isn't an insect. Your tarantula will consume the liquid from the cricket and leave a bolus behind. This is what's left once the cricket is drained dry. The mulch will be with it or dropped along the way.