Sentence: Honey must first have been known as a wild product, the bees...

[Volcano1985]

"Honey must first have been known as a wild product, the bees building their structures in hollow trees or holes in the rocks, or any similar cavity that chance offered."

Is there any grammatical mistake ? I couldn't understand "the bees building their structures in hollow trees or holes in the rocks, or any similar cavity that chance offered."

I think there is something missing like

"the bees xxx building their structures...."

[Ralf]

Bees build hives in hollows; i.e. trees and rocks (which are hollow).
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[Volcano1985]

Present Tense ?

[Yankee]

Hi Volcano

I'd call that a participial clause. To me, it basically gives a reason why the author wrote the first clause. Have a look here:
http://homepages.ihug.com.au/~qqqf/participleclauses.htm
.
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