Why are insects unafraid when you tap at them from the other side of glass?

Question

In the summer months we frequently try and kill mosquitos in our home. They are tremendously skittish and get airborne pretty quickly as you approach them. However, if they land on a piece of glass (a window for example) they don't seem at all bothered at you approaching from the other side and tapping the glass where they have landed.

Is this some strange physiology of insects (or at least mosquitos) that they cannot look down? Is it that their eyes function differently to our eyes and cannot see through the glass? For sure, their brains cannot be developed enough to understand the safety afforded by the glass.

Answer 1

Since insect brains do not contain enough neurons for higher level emotions such as fear, much of their behavior is programmed and reflexive. When you approach them, they have evolved to fly away. Glass, on the other hand is not something they evolved to "understand". They likely are not programmed to see something approaching them from below their legs as they are sitting securely on a hard substrate as a threat. They can look down. They just don't "get" glass.