On p.199 of Resident 5: The Complete Official Guide, it states in an interview that the Popokarimu is a Bat/Silkworm hybrid that's infected with a plaga parasite:
Early images of Popokarimu suggest a hybrid creature that looks more like a bat and a scorpion combined. What were the reasons for this particular design?
Jiro Taoka, Lead Designer: Popokarimu is a combination of bat and silkworm, invented when we planned to create a flying boss enemy. We heightened the red color on the weak point (abdomen) after play testing as it was decided it would be good to have this reflect the glowing of the sunset.
Yoshinori Matsushita, Modeler: We kept the idea that Popokarimu is a huge bat infected by Plaga but we changed his appearance from adult insect with hard shell to young, worm-like larva. The reason for this alteration was the look of the early image. That creature had too strong of a fantasy element, and lacked a sense of revulsion. So we changed him to increase the visual impact.
sorry for the late reply, been absent here a lot recently...
It was the guide published by Prima Games / PiggyBack Interactive, with the questions proposed to the dev team when asked about the various concept arts depicted different insect-like appearances for the Popokarimu prior to the finalized design.
And as my direct copy of the interview transcript implies, the Popokarimu is also allegedly a male of its species...
Whether that's worth noting or not, seeing as an insect's sexual dimorphism is frequently more dramatic than other species, meaning a theoretical female Popokarimu could've potentially looked far different, had such a thing existed.