Unfortunately, if you plan to go to warm areas and beaches, there's always the possibility that you may see very small lizards. They do tend to stay away from people, but if you look hard enough, you're liable to see them even in the rural areas.
I don't go looking for them, so I can honestly say that on many of our cruises we never see any.
Of course, you don't have to get off the ship in ports where lizards are more prevalent. Absolutely nothing bad about staying onboard, relaxing, reading a good book, or going to the spa while everyone else is off the ship. We do that every now and then, especially in ports where we've been many times or if they don't particularly offer us something we like to see or do.
If you really want to try a cruise, perhaps doing a Canada/New England cruise or possibly an Alaskan cruise might be something you'd like to do. Or maybe a river cruise in Europe if you want to do some traveling.
Hope you find something that will meet your needs and provide a wonderful experience.