Final answer:
In the sentence provided, 'the tarantula' is the direct object as it is the entity being acted upon by the verb 'stings'.
Step-by-step explanation:
The direct object in a sentence is the noun or pronoun that receives the action of the verb. To identify the direct object, you can ask 'what?' or 'whom?' after the verb. In the sentence 'The wasp stings the tarantula in its soft spot', the action is 'stings'. If we ask 'What does the wasp sting?', the answer would be 'the tarantula'.
Therefore, the tarantula is the direct object. The other options provided are not correct: 'wasp' is the subject performing the action, 'stings' is the verb, and 'spot' is not the direct recipient of the action.