Meerna eggs need to sit on top of very hot sand for an entire summer to hatch. The sand acts as a natural camouflage, as Meerna eggs are primarily brown. Despite the purple, fabric-like fur that grows around the center, it typically becomes covered in brown sand dust too so it doesn't spoil their cover.
Meerna eggs, for these reasons, are very difficult to find.
The Meerna are excellent salescreatures who often try to sell their "magical" goods to travelers passing through the Northern Plains. They strategically place their shops on Cave Road which links Leila to the Egg Cave. Typically, residents from Ark City take this road, so as to avoid the jungle and dangerous Volcano in the center of the island.
In terms of attitude, Meernas are very persistent, cunning, and understanding of humans and their various moods. It's what makes them so great at selling otherwise cheaply made goods to weary travelers.