Who made these winding designs on this birch tree? 

A snail has left a feeding trail! The birch tree is covered in an algal film, fine food for a snail. The snail’s radula, a tongue-like organ covered in small teeth, scraped off the algae in an intricate pattern of rows of short lines undulating from side to side. 

Snail radula magnified 400x.

This snail scraping might be beneficial to the birch. Clearing the bark could allow more sunlight to penetrate the birch’s thin outer bark and enable late-winter photosynthesis. The bark scrubbing could also help the bark reflect light, keeping the tree from heating and expanding on a sunny day and “frost cracking” at night.  

While the snails are likely now sealed in their shell and snuggled under the soil for winter, we can still read their stories on trees. 

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