Calcium does not replace gut loading. You need to feed the crickets a high quality grain to make them nutritious for your reptile and then you need to provide calcium and vitamin D3 to your reptiles, which is most effectively supplied by dusting the feeders. I don't know how well the spray will work and how long it will stay on the feeders. I use Repashy Calcium Plus. I put the feeders in a container, sprinkle on the supplement and shake the container. Of course if the feeders stay in the cage for a long time they will groom the calcium off themselves, but enough seems to get eaten right away to keep my reptiles healthy.