I always ask my students, "What is your job?". Many of them know the answer - to study, to learn, to get good grades. I tell them that, in our Garden, each living thing has a job too, and because of that, we never, ever kill any of them - the response is usually "Even ants/cockroaches/flies?". No, not even them. Many of the creatures that we don't like are part of nature's cleanup crew. They eat trash, other insects and various organic materials. Many of them are just not attractive, so we think they are "bad" - take a look at ladybug larvae. They also are food for the creatures that we DO "like" - birds. For instance, ants eat the larvae of many of the insects that would eat our vegetables and fruits, as well as fly larvae. We all know how beneficial earthworms are - ants are equally important in aerating and turning our soil, providing tiny tunnels for rainwater to seep into our earth. They are also pollinators, as they move from plant to plant.
If there seems to be "too many" creatures - we have many lizards for instance - it simply means that there is a lot of food for them. Like children finding where the ice cream store is, and when it's open, the creatures in the Nature Center and Garden find where the food is and hang out until it is gone.
If you have a garden, rejoice if you see many creatures in it - it means all is well and Mother Nature is creating a balance on her own. She is much older and wiser than we are....