The devotee can do good not only to humanity but to all living entities as well. Everyone can benefit spiritually by the chanting of the Hare Krsna maha-mantra. When the transcendental vibration of Hare Krsna is sounded, even the trees, animals and insects benefit. Thus when one chants the Hare Krsna maha-mantra loudly, he actually shows mercy to all living entities.
From Srila Prabhupada’s purport to SB 4.31.19