When you feel an insect land on your arm, or think you feel an insect land on your arm that isn't really there, which part of your brain is firing signals?

that would be called plucking : )

explanation:

''plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the erosion and transportation of individual pieces of bedrock, especially large "joint blocks". as a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints (cracks) in the bedrock."

when it is at an intermediate population density

it's d - life cycles - apex