Giant Mantises are carnivorous, and Tig plants are inedible to Wood Folk. As such, Tigs have no need for defenses against them, and have adapted to conserve spores when they pass by. Other, less familiar creatures will still trigger a release, however.
Spore Cloud is physical. Now that I look in the code, though, it looks like I somehow neglected to assign it an element! That'll be fixed in a moment.