What’s the difference between a 60mm macro lens and a 100mm one ?
Well the answer is how close to the subject you need to be to focus at 1:1, essentially that’s the minimum working distance on the lens, so with a 60mm lens you need to be closer from the subject to achieve a macro ratio of 1:1 or life size image than a 100mm macro lens. The key factor being with a shorter lens you need to be closer to the subject to get a 1:1 image.
You may wonder why this could be important, well it effects upon your photography use of the lens.
If you are trying to photography an active insect then being further away from the subject will allow you get more shots of it without spooking the creature, and makes it easier to exclude your own shadow from the subject by being further away from it. In butterfly photography many people will use macro lens of 150mm lens and longer to this end. Note however Macro buying lens of this focal length and greater, will greatly impact your wallet!