How did millipede form by rain?

Millipedes are not formed by rain; rather, they are a class of arthropods that develop from eggs laid by adult millipedes. However, after heavy rain, millipedes may emerge from their burrows or habitat in search of food or to mate, as the moist conditions are favorable for their activity. Rain can also lead to increased visibility of millipedes as they may be found on the surface of the soil or on vegetation during wet conditions.