After mating, the female will lay groups of 12-400 eggs in a frothy liquid that turns to a hard protective shell. This is how these insects survive the winter. Small mantids emerge from the mass in the spring. Often, the first meal is a sibling. It takes an entire summer or growing season for mantids to mature to adulthood and there is only one generation per year.
Pesticides drastically reduce the numbers of mantids in a given area.
If you desire to encourage mantids you should use as few pesticides as possible and allow some vegetation to grow to provide cover for the mantids. Collecting egg masses is not an effective method for increasing the population due to the fact that mantids tend to move away to find suitable coverage and food sources. Praying mantids have an association with many diverse pharmacological and religious beliefs. The Chinese write of the mantis as curing anything from impotence to goiter. They believed that roasting the egg masses and feeding them to your children will stop bed wetting, but suggested not eating the egg masses on an empty stomach for it will surely make a person sick.