Anyone know what species those insectoid headed droids are supposed to resemble? We first see one in the sand crawler in ANH, and since then they have appeared throughout the franchise including the CGI Clone Wars show.
It looks like an insectoid head with two large compound eyes on C3PO’s body, I’m guessing they are protocol droids for some insectoid species?
Yep, that is the one! Man this board is amazing 
But no clue as to why they have that face huh?
It depends on if you’re asking about them in-canon, or as behind-the-scenes.
They have that head because they do. When making a film like that, you churn out thousands of designs and the Director picks twenty he likes, and most of those get made, then scattered throughout the film in random places.
Canon-wise, there are many insectoid species in the Star Wars universe, one of the most prominent being Zuckuss, and alongside him was another insectoid droid that used a 3PO-like body, 4-LOM.
There is nothing in the Star Wars universe, no matter how small and insignificant they may have been in the movies, that does not have an extensive back-story and continuing side-adventures.
The action figure was called “Death Star Droid”, even though the first appearance in the movie was the junky one in sand crawler.
Thanks to the Kenner action figures, 4-LOM and Zuckuss will always be name swapped to me! 