About 20 years ago I ran through a bunch of different camera equipment, and in particular, tried out several different macro lenses. The 100mm macro lenses made by most manufacturers do quite well for most little critters. The exceptions, I found, were for:
A. Flying critters (which work better with a longer telephoto lens with a decently large magnification ratio) I use a 300mm lens (often with a 1.4x extender) for butterfly/moth/hummingbird shooting for this reason.
B. Really small creatures. Most macro lenses have a maximum magnification of 1:1 (meaning the image formed on the sensor is no larger than the size of the object in real life). Canon makes a specialty macro lens called the 65mm MP-E that goes up to a whopping 5:1 magnification that I've used for most of my bug shots for the last 15 or so years.
I love the MP-E, but it's a hard lens to use. No autofocus or image stabilization and depth of focus is razor thin. Really best if used on a tripod, but fun to try handheld nonetheless. Back when I had younger steadier hands I could routinely shoot the MP-E handheld at magnifications up to 3:1, but these days I rarely use it past about 1.5:1 and would probably be better served by one of the newer image stabilized 100mm macros.
