Tree dwelling snakes are the most aggressive. And hatchlings are the more agressive than adults. Tree dwellers have to rely on outrunning and then defending themselves where as other snakes rely on outrunning , display and then defense. When ground snakes outrun, the hit a destination..like a hole or something. Where as tree snakes still are in the trees and often when they are encountered they are sunning themselves and don't have the energy to flee (and not too different of a place to flee to) so they bite.
And Perkins did leave St. Louis a few times. He was the Zoologist on Edmund Hillary's later Himalayan expeditions, and did Zoological work in Chicago and in New York as well.