Then they could trace the energy of a specific person? Follow it back to them.

[Daqiang, no longer bothered by standing in the doorway, held one hand up and several butterflies appeared in his palm in a shimmer of blue energy. They were all clearly very 'full' and near to bursting, flapping erratically. Being around Daqiang himself was like being around a fountain of energy ready for the drinking.]

These ones have all failed to gather any energy but this venerable one's own.