Galina, I feel your pain. A few years ago I had purchased several conifers and had the pots waiting for planting. I went out to water them one morning and hundreds of grasshoppers came out of the soil of the pots. In less then a week all the plants were dead!
Here's grasshoppers of Florida. See if you can id which you have.
http://edis.ifas.ufl.edu/IN010
You should also find this helpful.
http://entnem.ufl.edu/ghopper/ghopper.html
Newt
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.