Bob Boner wrote:
If you want to photograph insects that fly away when you get close, I recommend a 150mm Sigma or the 180mm Canon (if you shoot Canon). You won't scare as many of your subjects if you are a little farther away from them.
Nikon has a 200mm macro that is very good, if you shoot Nikon.
The longer focal lengths help but are not needed for the vast majority of subjects. The downsides to the longer lens are bigger, heavier, more costly & less DOF...I have lots of macro images on my Flickr stream of insects shot with a 105mm macro (older MF model) that did not fly away. The secret is knowing the subject and their habits...