Tree Scaling

Short answer: Climbing a vertical trunk is hard for an animal with no limbs, and biologists have studied how snakes do it in detail. In a 2020 review, Bruce Jayne of the University of Cincinnati described arboreal concertina locomotion.

The snake grips a cylinder with alternating left and right bends, and keeps a grip with the uphill part of its body before letting go with the downhill part. It then stretches forward and pulls the rest of its body up. Concertina is reliable, but slow and energetically costly. On rough bark or among twigs and branches, snakes can also use lateral undulation, pushing against bumps and side branches with a wave that passes along the body. This needs something to push against; it doesn't work on smooth surfaces. In 2021, a team including Thomas Seibert, Julie Savidge and Jayne described a new mode in Current Biology called lasso locomotion. Brown tree snakes (Boiga irregularis) on Guam wrapped a single loop around smooth poles too wide for concertina, then inched upward by small bends moving within the loop. The discovery came from efforts to keep the invasive snakes away from nests of endangered birds. The footage shows a snake gripping a pale, smooth trunk at night with tight coils and moving up in stages. The source doesn't identify the species.