You should be aware that any zoom that says it's a macro, isn't. Such lenses usually have some means or other of getting moderately close at the maximum focal length which gives you a magnification ratio of between 1:4 and 1:2. This means on your crop sensor a subject 25mm long will fill between 1/4 and 1/2 of your field of view depending on the lens used.
For many, this is quite sufficient for shooting butterflies and dragonflies with a bit of the environment included in the picture, and most current sensors have enough pixels to crop a little.
The definition of 'macro' is an ability to magnify to 1:1, i.e. a 25mm long subject will fill your field of view. Such lenses are without exception of fixed focal length. They are usually expensive, and almost always, very sharp. Getting close means fighting narrow depth of field, light limitations and camera shake. The closer you get the harder it gets, and shooting macro can take a lot of skill and patience. The rewards can be high but many people simply decide that the trouble taken outweighs the benefits.
Unless you've already dipped your toe in the water with less expensive solutions, it might be worth trying one of the pseudo-macro zooms first. If you don't like it, at least you'll have a telezoom for other uses.