Why Do Bears Rub Against Trees? Scientists Offer New Explanation.

There are many reasons bears shimmy and scratch against trees. Sometimes they communicate by scent-marking trees, other times they’re removing hair and scratching that hard-to-reach itch. A new study posits an additional perk: slathering on nature-made tick repellent. When bears wriggle against bark, the tree scratching posts leak out tars, resins and saps. The thick tar of beech trees sticks to fur and skin the longest, and it is water-resistant, making it a strong contender for an effective tick repellent.

关于熊为何会蹭树或抓树，已经有了很多解释。有时候，熊会通过在树上标记自己的气味来互相沟通，其他时候他们需要去除一些毛发，或者通过蹭树给自己比较难触碰的部位挠痒。一项新的研究提出了一项蹭树的新好处：可以让身上沾满自然形成的驱虫物质。 当熊在树干上扭来扭去，树干被划破的部分就会溢出焦油、树脂和树液。山毛榉粘稠的焦油会在熊的皮毛和皮肤上黏得最久，而且可以防水，所以作为一项有效的驱虫手段脱颖而出。

tips

itch n. 痒；v. 发痒

tick n. 壁虱，滴答声，瞬间

repellent n. 驱除剂；adj. 令人讨厌的，隔绝的