What is the indirect object in this sentence: The mother wasp digs the tarantula a grave?
It would be tarantula
Think about it this way: What is the mother wasp digging?
A grave, right?
Who is receiving the grave? The tarantula.
NOTE: The mother wasp is giving the action of digging to the grave. Whenever we give direct action to an noun, that is the direct object.
The indirect object is the one receiving the direct object.
The tarantula is receiving the grave.
You can also remind yourself of the sentence pattern: Subject, Verb, Indirect Object, and Direct Object