Take another look at the sentence:
While Clive stood on top of the fire ant mound, several of the insects crawled over his shoes and __________ him on the ankles, sending the poor boy dancing around the yard and slapping at his legs.
The sentence requires the simple past of sting, an irregular verb. Stung is the simple past form.
|Verb||Simple Present||Simple Past||Past Participle|
Stang, the form you chose, is a spelling error. Before you continue, review the rules for irregular verbs.