Yup they are, the ones in the wild are toxic because of the tomato plants. You can buy them in all kinds of sizes, I'd say medium sized ones would be a good size for your frog. Don't buy a lot at once though if you try them, because they grow really fast and might outgrow your frog. To get them to eat the worms, I usually have to use tongs, dangling it in front of them and sometimes rubbing the frogs lip with the food item and they respond by grabbing the worm most of the time. Some of my frogs won't eat from tongs though so I'll just set the worm in front of them and hope that it moves enough to grab the frogs attention.