That... Always annoyed me too. At least my inner biology dipshit. It just seemed... off.
However, I think it is a problem with enemy physics. Spiders would be climbing walls and be the only enemy to do so. So disincluding them means they don't have to worry about their gravity being off.
However, I think it is a problem with enemy physics. Spiders would be climbing walls and be the only enemy to do so. So disincluding them means they don't have to worry about their gravity being off.