What you do think the white blobs to the top left of the fly’s head are?

Let me know your guess in the comments.
I’ll post the correct answer tomorrow evening. No cheating, no searching on the “university of google”!
Update
Answers will be held up until tomorrow. I’ll post the answer in a separate post (this one is likely to be gone from the top page by then).
Original or “silly” answers welcome. I’d encourage serious answers to give a justification if you can.

I’ll leave a slightly cryptic reply in case my answer is the right one: Is this perhaps one of several Drosophila species that display an unusual form of intra-specific competition?