Native snails on Hokkaido Island climb trees to avoid native predators, but this tactic can’t help them escape predatory invasive rats.
In a small region of Hokkaido Island, Japan, the slow-moving, athletically brilliant Sapporo Mai-Mai Snail (Euhadra brandtii sapporo) ascends the high canopy, escaping ground-dwelling predators. When winter gives way to spring, snails transition from hibernating on the forest floor to climbing native trees. This seasonal migration is a life-saving adaptation.
Land-dwelling, native Raccoon Dogs and Carabine Beetles have an appetite for escargot, but the tree heights offer a safe space for the snails. Professor Ikuyo Saeki from the University of Tsukuba and her colleagues are finding evidence that the survival rate of the tree-migrating snails is far greater than the individuals that stay on the ground. A number of snails choose not to climb into the tree canopy and become easy prey for a list of predators. The researchers also noticed an abundance of moss, lichen, and other snail-diet food in the trees. This could also inspire the Mai-Mai Snail to move higher. Defying gravity to avoid predators is believed to be the primary behavioral cause, but it’s nice know they are making tree-top dinner reservations as well.
Normally, tree-climbing would be an excellent way for snails to avoid predators and find food sources. However, this evolutionary-devised strategy is being thwarted by three species of invasive rats, known to eat snails, who have moved onto Hokkaido Island. Rats are expert climbers, and now that they’ve invaded the island, the snails in the canopy are highly vulnerable.
An animal climbing a tree in the face of immediate danger is a well-known defense mechanism. If invasive predators are in fact climbing trees and hunting snails, the success of this adaptive behavior declines. Although the snails’ seasonal migration is an act of preservation–a slime climb to safety–it won’t offer any protection against invasive rats.
In situations like this, conservation intervention can help. Removal of invasive species can restore native species’ natural conditions, such that their instinctual behaviors can help them survive.
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