After a rainstorm, snails can often be seen crawling up a tree. Although it is common for snails to come out of hiding during and after the rain, it seems strange that they would like to get up high on a tree trunk where they are exposing themselves unnecessarily. However, this exposure may actually still be safer than staying on the ground, where they are prone to be eaten by ground-dwelling predators.
An interesting study on this behavior was done on a particular species of land snail, Euhadra brandtii sapporo, in Japan.[1] These snails spend part of their time living in the forest canopy. During the winter they hibernate under the fallen leaves on the ground, but in the spring they crawl up to the tree tops where they live throughout the summer. During the fall they come back down again.
This detailed field study revealed that snails that spend the summer living up in the forest canopy have a higher survival rate than those staying on the ground.[2] In fact, in some cases their survival rate was almost twice as high. By staying in the tree tops, these snails avoid being eaten by ground-dwelling predators such as beetles, raccoons, and rodents.
Although most snail species are not “migratory” in that sense, it is plausible that there is a similar reason for their tree-climbing behavior. However, instead of going all the way to the top and staying there, many snails seem to only go up during a rainstorm, and then come back down again shortly afterwards, repeating the same behavior with every next rainstorm.
If they stayed somewhere halfway up a tree trunk, it would probably become too hot and dry for them once the sun comes back out again. In that case there is a good chance they will dry out and die. But during cooler and wetter weather it would allow them to escape from ground-dwelling predators, at least temporarily.
Snails that go all the way up to the canopy would likely find more protection against the sun, and are thus able to stay up there all the time. But snails that only go halfway up will have to come back down again to find cooler and wetter conditions, at the risk of becoming someone else’s meal. So, it appears that when you are a snail, it’s actually a good thing to be up a tree!
References
- University of Tsukuba. Scientists go out on a limb to study tree-climbing land snails. Phys.org, 31 March 2017.
- I. Saeki et al. Adaptive significance of arboreality: field evidence from a tree-climbing land snail. Animal Behaviour 127:53-66, 2017.