Site and Date of Introduction: The brown tree snake was introduced into Guam in the 1950s. The snake was first sighted inland from the seaport and became conspicuous throughout central Guam by the 1960s.By 1968, brown tree snakes had successfully dispersed throughout the island.eason(s) Why it has Become Established: The brown tree snake has become established on Guam due to the absence of natural population controls and the abundance of vulnerable prey on the island. For example, introduced lizards are popular food items for young snakes.