Praying Mantis 2 Egg Cases 100-400 Babies with Hirt's Hatching Habitat One the best solution for people how don't want to use dangerous chemicals in their garden to control insects. They eat about any bug except the valuable Lady Bugs. Simply refrigerate the egg cases until you are ready for your chemical-free insect control The average hatch time is 10-20 days. Most hatch at once, but some may hatching may take up to 8 weeks and we include the Hirt's Hatching Habitat so you can watch the egg case hatch.