Lack of food may lead to the crickets eating the styrofoam or if the smell of the food is on the styrofoam they will eat it too. Spinach is a poor choice for gutloading as it binds the calcium. You can gutload/feed the insects with a wide assortment of greens and veggies such as collards, dandelion greens, kale, endive, escarole, mustard greens, carrots, squash, sweet potato, zucchini, sweet red pepper, etc.