I thought it was also incorporating the wealth of myths involving animal spirits taking human form (such as the Huli Jing in China). Actually, there is a wide and varied wealth of folklore to draw upon.
Norse Berserkers could take the form of wolves and bears.
Mayan myth has eagle shapeshifters
Fox spirits in china and japan. Japan also has cats, badgers and racoons. China has lots of animal spirits taking human form, particularly after buddhism started takin root in China and the idea that animal spirits could 'earn' human form.
Selkie, were-seals of a sort, from scotland
Maras, she wolves, from Scandanvia
Naga were said to be able to take human form (in Malay, the kings decend from one such marriage..)
Snake shapeshifters appear in Tatar lore as a Yuxa, a snake shapeshifter, and the Madame White Snake tail in China.
Almost all Shapeshifters in RL myth are mammals or at least warm blooded. The exception are references to dragons, naga and the above snake examples.
I vaguely remember 'spider woman' from native american lore.. hmm... Hopi?
But actual insects? I havent found any examples.