Etymologist vs. entomologist

Which word means the study of word origins: etymology or entomology? The other word means the study of insects, but that is no help. You either know both words, or you probably know neither.

The old joke goes like this:
QUESTION: What is the difference between an etymologist and an entomologist.
ANSWER: Only an etymologist knows that answer.

It's funny (sort of) because an etymologist studies words; an entomologist studies insects; and the rest of us don't know nuttin 'bout neither.

Ha-ha.