Carolina praying mantis ootheca will hatch within 2-6 weeks. If you wish to delay hatching, simply keep the egg case in a refrigerator in a non-airtight container, then remove it 1-2 months before you want it to hatch. Each ootheca could hatch out anywhere from 50 – 200 baby mantis. This is a great educational opportunity for children to hatch these mantis indoors, and release into the garden. Great for invasive lantern fly pest control.