They are safe if you can get them to eat them. Mine won't touch them because they do not wiggle. They are good for them and the benefit, if you can get them to eat, are they provide a varity in their diet. I use super worms, crickets, meal worms, wax worms, red wigglers and a combination of raw hamburger or diced red meat (raw) and boiled egg whites. I also throw in some salad and berries but they tend to avoid them. It does attract the crickets though and the babies hunt around it. If you want to get them to eat the blood worms, thaw them out and mix some live meal worms with them. They will go for the wiggling meal worms and get the benefits of the blood worms as well.