It's a defense mechanism of the Christmas tree worm, most of which resides in a tunnel it carves into live coral.

这是圣诞树蠕虫的防御机制，它们中的大多数栖身在活珊瑚上挖出的“地道”里。

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The Catskill Mountain Railroad runs through a majestic tunnel of tree branches that looks like a cathedral.

卡茨基尔山铁路贯穿树枝的景观隧道，像一主教座堂。

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It had been planned that the tunnel would reach into a nearby forest, but the first man out emerged just short of the tree line.

原本计划是让隧道延伸至附近的一片森林中，但头一个爬出去的人却正好在树林边缘外现身。

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Those eggs are deposited in the tree's branches, but when they hatch (which they do two weeks after being laid), the resulting larvae fall to the ground and tunnel down to the tree's roots, from which they suck their sustenance.

ECONOMIST: The 17-year cicadas are about to emerge in force