A few years ago my herper friend Sleazeweasel opined that he was "not sure any snake is non-poisonous." Now, that was a novel idea to me, and thus was food for thought! My friend voraciously consumes herpetological literature, catches every snake if he can that he sees and photographs it, and travels around the world seeking wilderness adventures in some of the planet's most resplendent hotspots of biodiversity. Thus, I have learned to respect his opinions re serpents.
One anecdote that his statement prodded up from my gray sediments is about a blacksnake (Coluber constrictor priapus) and a southern leopard frog (Rana sphenocephala). I was delineating a wetland somewhere in north Florida when I heard a bleating sound behind me. A leopard frog was in the mouth of a blacksnake, the frog's body bent in ?agony, and the frog was screaming. The blacksnake dropped the frog to the ground at the very instant that the snake and I made eye contact, and quickly slithered off into the dense saw-palmettos (Serenoa repens), leaving the moribund frog behind.
The leopard frog was evidently dying and made no attempt to escape from me. I thought this was odd; blacksnakes are not supposed to be poisonous or constrictors (in spite of their scientific name), and the frog had not asphyxiated nor was it bleeding significantly. A few minutes later the frog ceased all movement and died. So what killed the frog?
Bryan Fry's work implies that SW was right and that the blacksnake may kill frogs with venom: