I had to commit a necessary evil today - euthanize an invasive Cuban tree frog. It was a baby so it wasn't easy, but once I captured it I couldn't legally re-release it.
I followed all steps recommended by the state of Florida:
After you capture the frog, we recommend that you euthanize them humanely -- in fact, it is illegal (and irresponsible) to re-release them into our ecosystem. The most humane way to euthanize Cuban Treefrogs is by liberally applying benzocaine (20%) to the back or belly of the frog.....After you apply the benzocaine, the Cuban Treefrog will quickly become unconscious. Next, seal the plastic bag and put it into the freezer overnight. By the next day, you can be sure that the Cuban Treefrog will not wake up (which would be inhumane), and can dispose of the bag.
...In Florida, the presence of this frog is NOT benign -- they are quite literally eating our native species alive, adding pressure to species that are already greatly affected by habitat loss. It is for these reasons that we advocate humanely euthanizing invasive Cuban Treefrogs -- help give our native wildlife a break!