Estivation in pixies is typically brought on by hotter weather and a dryer environment. It’s a natural process where the frog encases itself in a mucous membrane and it’s body goes into torpor. In the wild it happens during the dry season and the frogs emerge with heavy rains. It can happen in captivity but for the health of the frog it is best avoided as it can take a toll on the frogs body reserves. If your frog looks like it’s burrowing and encasing itself keep the substrate moister then usual. Provide a day/night cycle and maintain temperatures from mid seventies to low eighties.