What two life-threatening hurdles did the move to dry land present?

Respiration and desiccation

The transition from a purely aquatic existence to terrestrial life introduced two critical, immediate challenges that threatened the survival of early woodlice ancestors. Desiccation refers to the extreme danger of drying out, as exposed aquatic respiratory surfaces collapse rapidly in air. Respiration posed the problem of how to efficiently extract oxygen from the air while simultaneously maintaining the necessary moisture levels for gas exchange surfaces. The solutions developed to overcome these dual problems—a waxy cuticle to limit water loss and modified pleopods for breathing—define the woodlouse's current terrestrial adaptations and its persistent need for humidity.